MOTOR BEHAVIOR:
CONNECTING MIND AND
BODY FOR OPTIMAL
PERFORMANCE
Jeffrey C. Ives, Ph.D
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3
MOTOR BEHAVIOR: CONNECTING
MIND AND BODY FOR OPTIMAL
PERFORMANCE
Jeffrey C. Ives, Ph.D.
Professor and Graduate Program Chair
Department of Exercise & Sport Sciences
Ithaca College
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MOTOR BEHAVIOR: CONNECTING MIND AND BODY FOR OPTIMAL
PERFORMANCE
Copyright 2009 Jeffrey C. Ives, Ph.D
All rights reserved. This book is protected by copyright. No part of this
book may be reproduced in any form or by any means, including
photocopying, or utilized by any information storage and retrieval system
without written permission of the copyright owner.
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PREFACE
Classes in motor behavior are among those that many students go
into without much, if any, foreknowledge, and even less about how it can
add to their skills and abilities in exercise science. Most students, and even
many laypersons, have heard of biomechanists, kinesiologists, physical
educators, sport psychologists, and exercise physiologists. There is,
however, no such thing as a motor behaviorist. Instead, motor behavior
knowledge contributes to each of these subdisciplines, and by doing so
increases the applied skills of practitioners. The purpose of this book is to
demonstrate in very practical ways how basic and applied knowledge of
motor behavior can be used to enhance exercise prescriptions, devise
better strength and conditioning programs for athletes, formulate more
effective rehabilitation programs for injured recreational and high level
athletes, improve the coaching of motor skill proficiency, and contribute to
nearly every other venue served by exercise scientists.
So, then, what exactly is motor behavior and how can it help in
enhancing the knowledge, skills, and abilities of exercise scientists? In
short, motor behavior refers to how the brain and the rest of the nervous
system produces and controls purposeful and willful movement through
the musculoskeletal system. These movements may be as finely crafted as
a flirtatious wink or as explosive as an Olympic style lift. The study of
motor behavior involves understanding the physiology of the nervous and
muscle systems, but the example of the flirtatious wink reveals that
motives and intentions and other cognitive actions influence our
movements. The influence of cognitive actions on our movements, and
vice versa, forms the basis of the mind-body connection. With a separate
understanding of the mind and of the body a practitioner can devise
programs to improve one or the other, but it is the savvy practitioner who
understands the connection between mind and body and devises programs
that address the whole, and the whole is much larger than the sum of the
parts.
The motor behavior field of study suffers a bit of an identity crisis,
being called a number of different names depending on the specific focus.
Motor learning and psychomotor control are terms used to describe the
more cognitive (―mindful‖) components of motor behavior. These terms
are often used in cognitive psychology and physical education. Motor
control, neuromuscular control, neuromechanics, and movement
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neuroscience are terms referring to the more physiological (―body‖)
aspects of motor behavior. The term motor behavior is used here simply
because it is more descriptive in identifying the physiological and
psychological aspects of movement. Some terms are synonymous, some
are not — no term by itself fully describes what is encompasses the field
of motor behavior, or what is in this book.
The emphasis of this book is on application. Basic scientific and
theoretical principles are covered, but only insofar as necessary to
understand how to practically apply motor behavior principles in exercise
and sport science settings. Notably absent is in-depth coverage of
neuromuscular physiology. Instead, the reader is assumed to have basic
anatomy and physiology courses with coverage of the nervous and
musculoskeletal systems, and a course in kinesiology or biomechanics.
Also absent is broad coverage of motor learning concepts that are covered
in other texts. In its place is a focused coverage of selected motor learning
topics, like attention, that we have found to play a significant role in
applied settings. An introductory course in psychology, particularly
cognitive psychology, would be useful.
Examined first is the physiological aspects contributing to
movement – which we will call motor control – and then the psychological
aspects – which we will call motor learning. These are the ―easy‖ parts.
The hard part is figuring out how these work together. For example, how
do emotion and motivation influence the rate of motor unit activation?
Why do problem solving and other higher cognitive functions play a
critical role in regaining joint stability following injury? Conversely, how
do our proprioceptive and neuromuscular abilities (e.g., strength) influence
how we will think and act? It is questions like these that dominate the last
part of the book.
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TABLE OF CONTENTS
Preface
Chapter 1. Introduction to Motor Behavior and the Mind-Body Connection
Introduction
The Important of Motor Skills
Defining Goal-Directed Movement
Summary and Application
UNIT I: Motor Control
Chapter 2. Neuromuscular Physiology
Review of the Nervous System
Propagation of the Action Potential
The Motor Unit
Coordination Revealed
Summary and Application
Chapter 3. Neuromechanics
Mechanical Properties of Skeletal Muscle
The Muscle-Tendon Complex Modeled as a Machine
The Neuromechanical Machine at Work
Summary and Application
Chapter 4. Movement Production
Motor and Sensory Systems and Reflex Movement
Central Nervous System Initiation and Control of Movement
Summary and Application
Chapter 5. Movement Models
The Need for Models
Models of Movement
Reflex Models
Hierarchical Models
The Systems Approach
Summary and Application
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UNIT 2. Motor Learning
Chapter 6.Measuring Motor Skills
Motor Skill Classification
Measuring Motor Skill Performance
Inferring Learning
Stages of Motor Skill Learning
Characteristics of Stages of Learning
Transfer of Learning
Summary and Application
Chapter 7. Information Processing
Multiple Resource Theory
Memory
Attention
Intention, Effort, and Attention
Summary and Application
Chapter 8. Abilities and Individual Differences
Determining Abilities
Talent Identification
Summary and Application
Chapter 9. Instruction, Practice, and Training
Basic Concepts in Instruction
Feedback
Practice Organization
Mental Practice
Putting it All Together: A Model of Practice
Creating the Environment for Practice and Training
Summary and Application
UNIT 3. Mind, Body, and Brain
Chapter 10. The Neurophysiology of Learning and Training
Central Nervous System Adaptations to Learning
Exercise Neuroscience
Summary and Application
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Chapter 11. Muscle Tone, Posture, and Balance
Muscle Tone
Posture and Balance
Measuring Posture and Balance
Posture, Balance, Core, and Low Back Pain
Summary and Application
Chapter 12. Orthopedic Injury, Rehabilitation, and Prehabilitation
Orthopedic Injury
Controlling Joint Stability
Orthopedic Rehabilitation and Prehabilitation
Summary and Application
Chapter 13. Strength, Power, Speed, and Agility
Strength and Power
Psychophysical Mechanisms of Strength and Power Production
Functional Strength and Power and the Rise of Psychophysical
Training
Speed and Agility
Determining Strength, Power, Speed, and Agility Components
Summary and Application
Chapter 14. Psychophysical Training for Functional Health
Psychophysical Training for General Populations
Functional Training for Functional Health
Functional Health Evaluation
Exercise Prescriptions for Functional Health
Summary and Application
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CHAPTER 1
INTRODUCTION TO MOTOR BEHAVIOR
AND THE MIND-BODY CONNECTION
Chapter Outline
I.
II.
III.
IV.
Introduction
The Importance of Motor Skills
Defining Goal-Directed Movement
Summary and Application
Introduction
umans move in a vast array of ways, from the slightest twitch
using just a few muscle fibers to an explosive action using
nearly every muscle in the body. Movements are used to do
work, communicate messages, and display emotion. Muscles are also used
internally regulate physiological processes such as move food through the
digestive tract and pump blood. All of these muscle actions and
movements fall under the heading of what we call motor behavior.
In its simplest form, motor behavior refers to the nature and cause
of human movement. The term implies both physiological (motor) and
psychological (behavior) aspects to movement. Such movements include
moving the body through space (locomotion), posture and balance, and
manipulation (e.g., hand gestures, ball kicking). Movements may be slow,
deliberate, and intense with concentration. Movements may also be
automatic or reflexive, occurring with little or no voluntary thought. The
focus of this book is on goal-directed movements, which by definition
are intentional and voluntary acts with an outcome purpose in mind,
meaning that the mind plays a fundamental role in how movements are
produced and carried out. This separates goal-directed movements from
non-volitional movements in the body, like peristalsis in the
gastrointestinal tract or the beating of the heart.
H
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Motor behavior has physiological and psychological components
In studying motor behavior it is helpful to examine the two basic
components of human movement separately, and then as a whole. The
physiological component, motor control, is concerned primarily with the
systems that carry out movements, particularly the neurophysiological and
musculoskeletal systems. The term neuromuscular control is used
synonymously with motor control. The behavioral component, motor
learning, emphasizes the mind‟s role in acquisition (i.e., learning),
planning, and modification of movement and how information processing
and behavioral states regulate movement quality. In reality these two
components work simultaneously with one another. The illustration below
shows how the study of motor control emphasizes what is happening in the
“body” whereas motor learning emphasizes what is happening in the
“mind”; and that together they form a major part of the mind-body
connection.
MOTOR LEARNING
MOTOR CONTROL
memory
motor
learning
action
attention
motivation
arousal
anxiety
information processing
intention
cognition
emotion
perception
problem solving
spinal
cord
muscles/body/
movement
sensory FB
augumented FB
proprioception, hearing, tactile, vision, etc.
mind
brain
body
Psychophysics is the difference between sensation and perception
Sensory feedback processing typifies mind-body systems at work.
Sensory feedback is provided by sensory receptors and the peripheral
nervous system. These receptors detect stimuli from the external
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environment like temperature and from the internal bodily environment
like muscle stretch. The central nervous system gathers this information
and interprets meaning, a process called perception. Sensation and
perception are often erroneously used interchangeably only because we
often cannot determine what the actual sensation is, only how we perceive
it. The sensitivity and relationship between detection and interpretation is
called psychophysics. Interpretation is vital because how we interpret the
sensory information dictates our action, not the sensory info itself.
A myriad of psychological factors determine what sensory
information is used, why it is used, and how it is used. Emotion,
reasoning, intention, motivation, and memories are notable psychological
factors that influence the interpretation of sensory information. These
factors determine if information is stored and give rise to meaning and
importance. Interpretation of stimuli data may be incorrect because of
disordered behavioral states and because of inaccurate sensory detection.
Psychophysics is used in many different areas. Borg's rating of
perceived exertion (RPE) scale and visual-analog pain scales are
applications of psychophysics. Graded exercise tests are often stopped
when someone points to the
highest workload on the RPE
scale – even if heart rate and
other physiological measures
indicate the person can go longer.
In ergonomics, work limits are
mostly set according to what is
perceived as a work limit, rather
than what physiological data may
indicate.
Utter, AC et al.. Med. Sci. Sports Exerc. 34:139-144, 2002.
The Importance of Quality Movement
The motor system provides the primary way in which humans
interact with the world. Consider, for example, that speaking, writing, and
“body language” are the main ways humans communicate, and all rely on
neuromuscular processes to carry out behavioral intentions. Many of our
most beautiful and transcendent accomplishments are carried out through
skilled movements, including music, art, sport, and survival. Rage is beat
out on drums or with fists, love communicated through tender touches, joy
expresses with jumps.
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But is it necessary that we learn to improve our movement control
aside from that gained during normal day to day life experiences?
According to Higgins (1991) it is important to enhance our movement
capabilities because it extends problem-solving capabilities, and by
extension, our ability to interact with the world. Movement quality plays
an important role in personal independence, as individuals learn to walk,
ride a bike, and drive. The consequences of poor motor behavior in
activities like driving can be severe. The decline in movement skills with
aging provides a clear example of how poor movement can negatively
impact the quality of one‟s life.
Specifically for exercise and sport scientists, it is well known that
the primary distinction separating the highest level athletes from simply
“high level” athletes in many sports, is motor behavior. The most difficult
part of most athletic rehabilitation programs is not gaining back
physiological capabilities (e.g., muscle strength), but rather, is gaining
back movement control. Neuromuscular and perceptually based training,
apart from standard physiologically based training, has been shown to
reduce injuries in athletes, improve athletic performance, improve work
productivity and lessen work-related injuries, improve physical function in
elders, and improve life quality in many populations. There are other
health and wellness implications as well, as those individuals with better
movement quality may have fewer risks for things like cardiovascular
disease (Houston et al., 2002).
Defining Goal-Directed Movement
A fundamental concept in motor behavior is, of course, goal
directed movement. The most practical ways to understand motor
behavioral processes is by examining and analyzing movement, in
particular, what we call motor skills. Motor skills are defined as actions
requiring voluntary body and/or limb movements to achieve a goal. A
particular motor skill may involve large and small muscle forces, slow and
deliberate thought, or rapid reactions. Sometimes they are done without
any apparent thought whatsoever. Motor skills can be performed poorly or
with great skill. Here we define several terms used to describe motor skill
characteristics.
Skill requires ability, but not vice-versa
It is important to evaluate the quality of motor skill performance
along with the type of movement. The quality of performance is defined as
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the level of skill. Being skilled is separate from having ability, which is
defined as a general capacity of an individual that is related to the
performance of tasks. For example, running speed is an important ability
contributing to successful performance in long jumping, baseball, and
many other sports, but in and of itself does not mean that one will have
skilled performance. One may have much ability, but little skill. On the
other hand, having high levels of skill requires ability. Ability should not
be thought of as a genetic component and skill a learned component.
Abilities fall into many categories, some of which are genetic, some are
learned, and many are a combination of both. Categories of abilities
include physical proficiency (e.g., strength, power, flexibility, lung vital
capacity), cognitive (e.g., information processing speed, memory,
emotional control), and perceptual-motor (e.g., finger dexterity, precision
and aiming control, multilimb coordination, kinesthesia and balance
control).
Motor skills require a cognitive component
Perceptual motor skill and psychomotor skill are terms used to
describe motor skills with specific features that require a large amount of
cognitive effort and/or sensory feedback. This can be most any motor skill
depending on the circumstances. By definition, these terms refer to
movements that have any of the following features: a reaction time
component (especially choice reaction time), require high levels of
dexterity, precision, or accuracy, require high levels of timing or rate
control, or require steadiness or speed of the hands or fingers. The term
perceptual motor skill is specifically used to describe movements that arise
from choices made from interpreting environmental cues (example below).
This generally excludes movements like running,
Coordination is often used
walking, and whole body equilibrium and
erroneously used to mean skill.
coordination.
It is easy to identify a skilled
performer as being coordinated,
In real life most motor skills are perceptual.
but this is not always the case.
Sports, driving a car, and walking down a busy street
Coordination refers to
all require considerable cognitive control. Vertical
patterning of body and limb
jumping provides a good example. In the lab, vertical movements relative to the
patterning of the environment
jumping is not considered a perceptual motor skill.
(objects and events). Thus, a
There is little cognitive effort, no reaction to a
coordinated movement must
stimulus, minimal precision, and little
take into account the context in
arm/hand/finger dexterity or coordination is needed.
which it performed and the
On the other hand, vertical jumping in a soccer game
constraints imposed by the
environment.
as part of a heading movement is psychomotor. The
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player must anticipate ball trajectory, time the jump, jostle and „feel‟ for
position, aim the jump to position the head, consider where to head the
ball (keeping in mind teammates, defenders, and game situation). The
jump is now a complex movement requiring more than explosive muscle
strength to be carried out successfully. In fact, it is the perceptual part of
many motor acts that determines the efficiency, coordination,
appropriateness, and overall effectiveness of the motor act.
Summary and Application
Motor behavior involves study of the physiological systems
producing movement and the psychological systems involved in planning,
learning, and regulating movement. This connection between mind and
body implies that behavioral actions in the mind are transferred to the
body, and actions in the body are transferred to the brain. Motor behavior,
as much as any academic discipline, examines this relationship and
provides insight to practical uses of the mind-body connection.
Practical use centers on training or challenging both systems
simultaneously to create more effective gains and better performance. How
this is done is emphasized throughout this text.
Bibliography and Other Sources
Shumway-Cook, A., & Woollacott, M.H. (2001). Motor Control:
Theory and Practical Applications. Lippincott Williams & Wilkins
Magill, R. (2003). Motor learning and control: Concepts and
applications. McGraw-Hill
Mathiowetz, V., & Haugen, J. (1994). Motor behavior research:
implications for therapeutic approaches to central nervous system
dysfunction. The American Journal Of Occupational Therapy, 48(8), 733745
Higgins, S. S. (1991). Motor skill acquisition. Physical Therapy,
71(2), 123-139.
Houston, T., Meoni, L., Ford, D., Brancati, F., Cooper, L., Levine,
D., & Klag, M. (2002). Sports ability in young men and the incidence of
cardiovascular disease. The American Journal of Medicine, 112(9), 689695.
17
UNIT 1
MOTOR CONTROL
Motor control is the study of the nervous system and musculoskeletal
systems regulating movements. In this unit we will focus on how these
systems work as a unit, and less on the precise cellular level function, with
the main objective being to determine rules or guidelines for how the
neuromuscular system works. Specifically, we will focus on how the
nervous system activates the muscles and what must be done to produce
movements that are efficient and effective. The role of the sensory system
and reflexive movements are examined as well as voluntary movements.
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CHAPTER 2
NEUROMUSCULAR PHYSIOLOGY
Chapter Outline
I. Review of the Nervous System
II. Propagation of the Action Potential
III. The Motor Unit
IV. Coordination Revealed
V. Summary and Application
Review of the Nervous System
he human nervous system can be divided into the central
nervous system (CNS) and the peripheral nervous system
(PNS). The CNS includes the brain and spinal cord and is the
integration and command center for the entire nervous system. The PNS
can be divided into sensory and motor divisions. Sensory (afferent)
division sends signals from the periphery to CNS. Motor (efferent)
division sends signals from CNS to effector organs, namely the muscles.
The PNS can also be divided into autonomic (involuntary) and
motor (voluntary) systems. In this context the motor system is defined as
that controlling voluntary motor behavior. The autonomic system used to
regulate bodily processes at the subconscious level, including heart rate,
ventilation, digestion, and other systems involving smooth muscle and
glands. The autonomic system can be further divided into the sympathetic
and parasympathetic divisions. Though the autonomic systems do play a
supporting role in motor behavior, we will only consider them in brief.
T
Sensory, motor, and interneurons define neuron function
At the heart of the nervous system are neurons; the nerve cell.
Neuron cell bodies (soma) house typical cellular organelles and the
nucleus. The key working features of neurons are the cell processes,
including dendrites and the axon. Dendrites branch from the cell body
acting as receptive sites for signals from other neurons. The dendrites
19
conduct impulses from synapses to the cell body in a manner called graded
potentials.
The axon is a single, generally long, process arising from a part of
the cell body called the axon hillock. Long axons are also called nerve
fibers. Axons may branch into axon collaterals and then into smaller
branches called terminal branches. Axons transmit action potentials away
from the cell body to synapses on other neurons. Large diameter axons
transmit signals faster than small axons. Myelin sheaths insulate the axon
and enable faster action potential conduction velocity. Gaps in the sheath,
called nodes of Ranvier, help speed conduction velocity through a process
called saltatory conduction.
soma
axon with
myelin sheath
axon
collaterals
dendrites
hillock
terminal
branches
nodes of Ranvier
Neurons are classified in a number of different ways. The
functional classification is based on direction of impulses; either toward or
away from the CNS. A structural classification of neurons based on
number of processes extending from soma, as unipolar, bipolar, or
multipolar.
Functionally, sensory neurons transmit information from sensory
receptors in the PNS toward the CNS. These signals normally ascend (go
up) toward the CNS, hence they are afferent. Most sensory neurons are
unipolar, the cell bodies of a group (i.e., a nerve) of these neurons are
generally grouped together in a bulb-like structure called a ganglia. The
ganglia of spinal nerves lie just outside the spinal cord. Motor neurons
carry signals away from the CNS (generally they descend) to the effector
organs, and are thus also
called efferent neurons.
dorsal root
sensory neuron
sensory neuron axons
cell
bodies
Most are multipolar and
interneuron
gangion
the cell bodies are in the
CNS (e.g., a motor
neuron innervating a
nerves
muscle has its cell body
in the anterior horn of
spinal
the spinal cord).
nerve
motor neuron
axons
ventral root
spinal cord
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Interneurons lie between motor and sensory neurons, linking the sensory
and motor divisions. Most CNS neurons are interneurons.
A cluster of neuron fibers enclosed within a connective tissue
sheath is called a nerve. Nerves may contain only afferent or efferent
fibers, but typical spinal nerves contain both afferent and efferent fibers.
The typical arrangement of sensory and motor fibers, interneurons, spinal
nerve, ganglion and sensory nerve bodies, is shown.
Propagation of the Action Potential
Generating the action potential requires a coordinated effort
Synapses form the junction between two neurons, and enable a
neuron‘s electrical signal to traverse from one neuron to another. Synapses
allow passage of signal in one direction only and may occur between axon
and dendrite, axon and cell body, and axon to axon. The more synapses
along a neuron chain, the slower the transmission of the signal.
Monosynaptic paths have one synapse, polysynaptic pathways more than
one synapse. The neuron on the transmitting end of a synapse is called the
presynaptic neuron and the receiving neuron is called the post-synaptic
neuron. There are many different types of synapses, for our purposes we
will only consider chemical synapses and the neuromuscular junction.
The electrical signal transmitted down the axon and to other
neurons is the action potential. The action potential is a bioelectric signal
that does not degrade as it travels down an axon or as it travels from one
neuron to another neuron or from neuron to effector organ, like muscles or
glands.
The synapse is a specialized part of neuron that mates with another
neuron. In chemical synapses it works to transmit the action potential by
sending chemicals from the presynaptic side to the postsynaptic side.
When the action potential in the presynaptic neuron reaches the end of the
axon (axon terminal) where the synapse is located, it causes small
containers called synaptic vesicles to release a neurotransmitter. The
neurotransmitter, such as
acetylcholine (ACh) floats
across the synaptic cleft (the
actual space between the
neurons) to bind to the
axon
postsynaptic axon terminal.
hillock
The neurotransmitter causes
the postsynaptic side to
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generate depolarizing currents in the postsynaptic neuron.
Action potentials are generated in a neuron based on the amount of
electrical impulses coming into that neuron. Dendrites on the cell body
receive depolarizing stimuli from other neurons that synapse on them.
These stimuli cause the postsynaptic neuron cell membrane to depolarize
in a graded fashion, and these depolarizing currents travel to the axon
hillock. At the hillock the graded potentials will sum, and if the total
current is strong enough, an action potential will be created. The amount
of current needed to create an AP is considered the threshold level. The
more neurons acting on a post synaptic neuron at a given time enables
more summation of the graded depolarizations, and thus a greater
likelihood of forming an action potential.
Temporal and spatial summation and EPSP/IPSP ratios all contribute to
action potential generation
Depolarizing stimuli on the post synaptic side can be excitatory
(excitatory post-synaptic potentials or EPSPs) or inhibitory (IPSPs).
The summing of the EPSPs can occur over time (temporal summation)
from a single presynaptic input or from several different inputs (spatial
summation). Thus, to generate an AP in the post synaptic neuron, there
can be summation of rapid firing EPSPs from the pre-synaptic neurons, or
summation of many different EPSPs from different pre-synaptic neurons.
Of course, there can be a combination of both temporal and spatial
summation. Also, some of the depolarizations will be inhibitory (IPSPs),
which stop the formation of EPSPs, essentially reducing the amount of
graded depolarizations summing at the hillock and effectively reducing the
likelihood of an action potential. Thus,
not only is generation of an action
potential dependent on temporal and
spatial summation, but also on the
ratio of excitatory to inhibitory inputs.
A general schematic depicting
formation of a action potential is
illustrated below. Consider a single
motor neuron whose cell body is in the
spinal cord and axon terminates on a
muscle fiber. The inputs, both
inhibitory and excitatory, come from
other motor neurons, sensory afferents,
interneurons, and direct connections
22
from the brain. To ―fire‖ this neuron (and subsequently activate the
muscle) the neuron membrane potential must change to reach a threshold
level. To do so the brain controls a precise combination of spatial inputs,
temporal inputs, and the ratio of EPSPs to IPSPs. The resting membrane
potential of the motor neuron is about -70mV, and in order to form an
action potential the membrane potential must be changed to -50mV. After
this -50mV threshold level is reached the cell membrane will undergo a
rapid depolarization in the form of an action potential.
Neurons can also be facilitated or inhibited
Not enough EPSPs or too many IPSPs cause sub-threshold changes
that are not sufficient to cause an action potential. However, staying in this
sub-threshold state has benefits in that the neuron is more ready to fire, or
less likely to fire. A neuron primed to fire is in a facilitated state, and can
be fired quicker and with little additional neural input. Actively subduing
the neuron to make it less likely to fire is called inhibition. Inhibition is a
result of more IPSP inputs that move the resting membrane potential away
from the threshold level.
Changing the temporal and spatial summation and ratio of EPSPs
to IPSPs not only allows facilitation, inhibition, and generation of the AP
itself, but also controls the firing rate of the neuron. As we see below,
controlling firing rate of a motor neuron can dramatically influence the
force output in muscle.
Millions of synapses may participate in the contraction of a single muscle
Controlling the generation of a single action potential in a single
neuron is intensely complex and little understood. This complexity can be
seen in a single motor neuron that has about 10,000 excitatory and
inhibitory inputs upon it. To form a single AP, or a specific firing rate of
APs, the brain must mix and match the temporal and spatial summation
and the ratio of EPSPs versus IPSPs. Scientists have little idea how the
brain does this, let alone how an entire muscle is regulated. A muscle
served by a motor neuron may have about 500 other motor neurons going
to it, making for about 5,000,000 synaptic connections that must be
monitored for this single muscle to be controlled. Going further, consider
that even in a simple leg kick maybe a 100 or so muscles are controlled,
meaning about 500 million synapses are involved. And this is only at the
level of the spinal cord, which does not compare to the complexity in the
brain.
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The Motor Unit
The motor unit is the basic unit of nervous system control
Motor neurons are connected at the distal end of their axons to
muscle fibers via synapses called neuromuscular junctions. The motor
neuron axon branches off and can attach to just a few muscle fibers or
hundreds of muscle fibers. A motor neuron and all the muscle fibers it
innervates is defined as a motor unit (MU). A motor unit pool (or
motoneuron pool) is a grouping of all motor units that activate a particular
muscle or muscle group.
Each motor neuron can excite from 15-2000 muscle fibers
depending on the particular muscle. The innervation ratio is the ratio of
one neuron to the number of muscle fibers it innervates. Muscles used for
finer control have smaller innervation ratios and gross movement muscles
tend to have larger innervation ratios. For instance, the first dorsal
interosseous muscle in hand has about 120 motor neurons and 41,000
muscle fibers for an average ratio of about 1:342. A typical
gastrocnemious muscle has about 580 motor neurons and 1,120,000
muscle fibers for an average ratio of 1:1931. All fibers within a motor unit
are the same type.
nerve
mu1
mu3
mu2
muscle
Motor units can be characterized by size, morphology, and function
Small motor units are defined as motor units with small neurons
(axon diameter and soma size), and large motor units have neurons with
large axons. Generally, small motor units also have few muscle fibers and
large motor units have many muscle fibers. The motor unit size definition
is largely comparative as there is no precise axon size or innervation ratio
separating small from large motor units. However, small and large motor
units also tend to have certain characteristics.
24
Small motor units also tend to have slow twitch fibers (Type I or
aerobic), large motor units tend to be fast twitch (Type IIB or IIX, FG,
anaerobic). Intermediate size motor units may have type I or an
intermediate fiber type like type IIa or FOG. Note that while the trend is
for slow twitch fiber to have small innervation ratios and fast twitch to
have large innervation ratios, such is not always the case and may vary
between genders and among muscles. For example, a large motor unit
with fast twitch fibers in the hand may have a relatively small innervation
ratio compared to a large motor unit in the rectus femoris muscle. Note
that muscle fiber type does not correspond to muscle fiber diameter.
According to data from Chalmers (2011), slow twitch and intermediate
type muscle fibers may be just as large, or larger, than fast twitch
glycolytic fibers.
Large motor units have larger diameter neurons that directly
influence their recruitment. Large neuron cell sizes in large motor units
generally need higher level of stimulation to reach threshold levels in order
to be activated (see below), although the threshold level itself is the same
as for smaller motor units.
An important characteristic associated with slow twitch motor
units is that slow twitch muscle fibers tend to have more muscle spindle
sensory receptors surrounding them. Actions of slow twitch muscle fibers
may thus stimulate more muscle spindle sensory activity than fast twitch.
The significance of this we will discussed later.
Motor unit behavior adheres to certain principles
Motor units are the most fundamental unit of movement controlled
by the brain. The brain can selectively activate just one motor unit or
thousands upon thousands. There are certain ―rules‖ that govern the firing
of a motor unit. Primary among these are the all-or-none principle and
the size principle of recruitment.
The all-or-none principle refers to the activation of muscle fibers
within each motor unit. All muscle fibers contract or none contract. When
the action potential in the motor neuron reaches the end of the axon it
effectively splits and races undegraded down each axon collateral toward
the neuromuscular junction. The action potential on the presynaptic neuron
side creates what is called an end-plate potential on the post-synaptic
muscle membrane. End-plate potentials are generally strong enough to
generate a muscle action potential (MAP) and thus a muscle contraction.
There is no need for spatial or temporal summation at the neuromuscular
25
junction, as a single action potential sent down the neuron is capable of
causing a muscle contraction in each muscle fiber.
Motor units are typically recruited by size based on Henneman‘s
size principle of recruitment. That is, small motor units are recruited first,
followed by larger motor units. Motor units are derecruited in reverse
order. The primary reason for this is because larger motor units have larger
diameter motor neurons which need a larger level of stimulation to be
reach the critical threshold level and thus be activated. Coupled with the
larger size neurons, larger motor units may have other morphological
characteristics that delay their recruitment, such as number of dendrites,
axon diameter, tissue electrical resistance, neurotransmitter receptor
sensitivity, and distribution of synapses on dendrites and soma.
The benefit of having small motor units recruited first cannot be
underestimated. Small motor units enable finer control of movement, and
the fatigue resistance of the slow twitch units
The electrical activity of the muscle
action potentials can be recorded
enables them to be ―first in and last out.‖
with electrodes in a process known
The consistency of the size principle always
as electromyography (EMG).
Electrodes can be inserted into the
holding true is under some debate, as there are
muscle (indwelling) or placed on
research reports documenting larger motor units
the skin surface above the muscle
(surface EMG). A single muscle
being recruited before smaller motor units. And
twitch can be recorded as the sum
although we will consider the size principle to be
of all potentials from all the fibers
in a motor unit. Generally this can
mostly true, understand that other influences to the
only be done with indwelling
motor neuron pool could cause some out-of- order
electrodes. Whole muscle EMG,
known as the EMG interference
recruitment. The type (e.g., concentric vs.
pattern, is the sum of all potentials
eccentric), speed, amount of sensory input, and
from all motor unit muscle fibers
that are in the electrode pick-up
intent of the contraction all have been inferred to
area.
influence recruitment order, as has training.
Motor unit behavior controls force output by recruitment, rate-coding,
and coordination
Motor units are activated for one fundamental purpose; and that is
to control the force of muscular contractions. Motor units are activated to
control small amounts of force within an individual muscle, and activated
to control whole limb and body movements. The nervous system regulates
three basic factors to control force output; 1) recruitment of motor units,
2) rate-coding of motor units, and 3) coordination of motor units and
muscles.
26
Motor unit recruitment changes the amount of active muscle tissue
Muscle force output can be changed by increasing or decreasing
the number of active motor units, which effectively increases or decreases
the amount of active muscle tissue. This activation follows the size
principle of motor unit recruitment: small motor units are activated first
followed by larger motor units. Because the larger motor units tend to be
fast twitch with more muscle fibers, activating more motor units generally
results in a large jump in the amount of active muscle tissue.
The larger, fast twitch, motor units are not typically activated until
at least 60% of maximum force output. Some motor units not activated
until 85-90% of maximum force output, but this is highly dependent on the
individual muscle. The adductor pollicis, for example, may have all units
recruited at about 55%, whereas in the biceps b. all units may not be
recruited until about 85%.
The observation that some motor
units may not be activated until
about 85-90% of maximum force
output has serious implications for
strength training. What are these
implications?
Rate coding changes the force-generating capacity of the muscle tissue
When a single action potential reaches the muscle and causes a
muscle action potential, the muscle will respond in the form of a single
twitch contraction immediately followed by relaxation. When repetitive
action potentials reach the muscle fibers they cause the muscle to twitch
repetitively. These repetitive twitches allow tension to increase by
27
summating, because there is not enough time for the muscle to relax. The
firing rate of the action potentials will match the firing rate of the muscle
twitches. Modifying the firing rate to increase or decrease force output is
termed rate coding.
Human muscle firing rates range from a minimum of 4-5 Hz to a
maximum of about 50-60 Hz. Contrary to popular intuition, slow twitch
fibers have faster maximal firing rates than fast twitch fibers. Fast firing
rates cause tension summation in a couple of different ways. First, with
repetitive action potentials there is not enough time for calcium to be re-
1
2
tension
tension
twitches
twitches
4
3
TETANUS
tension
tension
twitches
twitches
FUSED
TETANUS
uptaken, resulting in an abundance of calcium in the muscle cell. This
leads to a maximal number of cross bridges forming. Also, since there is
not enough time to relax the elastic elements in the muscle, they remained
stretched and thus tension is increased. If the twitches are fast enough a
state of tetanus will occur. In humans, under artificial stimulation, tetanus
can increase the force output of a muscle over a single twitch by 1.5 to 10
times. It is questionable whether tetanus is a normal occurrence in
humans, though. Like motor unit recruitment, the fastest firing rates are
not seen until higher intensity contractions. For example, Conwit et al.
(1999) noted stable firing rates in the quadriceps up to 30% MVC, and
steady increases until 100% MVC.
So how does the nervous system mix and match motor unit
recruitment and firing rate? If more force is needed are motor units added
or firing rates increased? Both happen, but exactly what happens is
dependent on the particular muscle and type of movement. Small muscles,
such as in the hand, may have full motor unit recruitment at 30% of
maximum force, then all additional force is due to rate coding. Larger
muscles may to do more rate coding early and not fully recruit all motor
units until 80-90% of maximum force. The motor units recruited earliest
tend to rise rapidly in firing rate then level off or plateau. The MUs
28
recruited later tend to rise rapidly in a linear manner. The leveling off is
indicative of tonic motor units and these motor units are likely slow
twitch. The linear motor unit recruitment is considered phasic and these
motor unit are more likely fast twitch. These early recruited tonic motor
units can stay active for longer time, most likely because of their fatigueresistant aerobic metabolism.
Many other factors influence the interplay between recruitment and
rate coding. For example, static contractions and dynamic contractions
done at the same relative workload have different recruitment and rate
coding behavior, and the same goes for concentric versus eccentric
contractions (Sogaard et al.,1998; Kossev & Christova, 1998).When new
motor units are recruited it has been speculated that the already active
units slow their firing rates (by a process called disfacilitation) in order to
smooth out the force increment (Broman et al., 1985), but not all scientists
agree with this observation (Kamen & Du, 1999). Clearly, exactly how
recruitment and rate coding work together is not fully known.
The aging process has a clear impact on motor unit behavior.
Starting about age 50 or earlier, and certainly by the 60s and 70s, changes
in muscle physiology and CNS function alter the way motor units are
recruited and firing rates modulated. In brief, in young people the fast
firing rate units (small, slow twitch) are normally recruited first, but this is
not necessary the case in elders. During sustained constant force
contractions the firing rate tends to
decline in young persons in order to
A note on EMG. It would seem that an increase in MU
recruitment – which also means larger MUs recruited –
avoid fatigue, but not in elders.
and and increase in firing rate, would not only increase
Overall, average firing rates tend to
force but electrical activity as measured by EMG. This
is true, but only to a limited extent for isometric
slow in the elderly, and recruitment
contractions. There are many other factors involved in
modulating electrical activity as detected by EMG that
thresholds tend to get lower, which
makes is difficult to relate EMG to force.
may reflect a shifting in fiber type
from Type II to Type I. Last, the
High
muscle action potentials are often
multiphasic, i.e., reflecting a
disordered action potential that may be
a result of a denervation—
reinnervation process that seems to
happen in aging (Erim et al., 1999).
Low
Some of these factors may be the
Low
High
Muscle Force
reason why elders often use different
strategies to control force output
(Graves et al., 2000).
29
Coordination is the most important way force output is controlled
Neuromuscular coordination is the most important way the
nervous system controls muscle force output, from within-muscle force to
whole body force expressions. Coordination can include timing of muscle
activation (e.g., agonist-antagonist timing), regulation of synergist
muscles, inhibition of antagonist muscles, altering the amount of cocontraction, and whole body sequencing – all of which fall under the
heading of intermuscular coordination. Intermuscular coordination is
defined as coordination of muscle groups and limbs and other body
segments. Coordination also includes the timing and regulation of motor
unit recruitment and firing rates, which is part of intramuscular
coordination (defined as coordination within a muscle). Both inter- and
intramuscular coordination are crucial in regulating muscle strength and
power and movement accuracy in real life activities
Intramuscular Coordination. We have already seen how motor unit
recruitment and firing rates are mixed and matched to meet the task
demands. This is at the core of intramuscular coordination, but there are
specific control processes used in specific situations. One process is
synchronization. Motor units tend to fire asynchronously, that is, out of
timing with one another, which provides for smooth movements.
However, some research data indicate that at times the activation of
different units, and especially the firing rates of already active units,
become synchronized to fire all at the same time. This ―pulling together‖
behavior enables an explosion of force. This is analogous to all members
of a tug-of-war team pulling all at once with one big final heave-ho to win
the contest.
Along these same lines as synchronization is alteration of the firing
rate pattern, or discharge patterning. A rapid doublet or triplet (2 or 3
rapid impulses) can increase the tension output greatly, and even if the
firing rate returns to normal the tension may remain high, which may
lessen the metabolic cost. Another form of discharge patterning is muscle
wisdom. Muscle wisdom refers to the change in discharge rates during
fatigue. During fatigue there tends to be a calculated slowing of a motor
unit‘s firing rates that is not due to physiological reasons like the buildup
of metabolic wastes. This slowing seems to be an automatic response in
healthy muscle to balance force output with energy sparing. Muscle
wisdom has also been ascribed to an initial high firing rate to ―jump start‖
a contraction, and then the firing rate declines (Conwit et al., 1999).
Muscle wisdom is an adaptive process that matches the neural activity to
30
the changing conditions of the muscle, and is controlled in some fashion
by the muscle itself (Kuchinad et al., 2004).
Among the most newly explored intramuscular coordination
mechanisms is the control of individual parts of a muscle.
Compartmentalization (Richmond, 1998) refers to smaller and
independently controlled groups of muscle fibers contained within a single
muscle or group of muscles (e.g., quadriceps femoris). These
compartments might be based on muscle morphology (a group of slow
twitch or fast twitch), or on neural recruitment (a particular part of the
muscle may only be activated during certain movements or force
requirements) or on different biomechanical functions. Biomechanical
compartments are well known, for example the shoulder
deltoid has long been identified as having medial, anterior,
1 2
and posterior compartments. Yet new compartments
continue to be identified, such that even the old three
compartment deltoid is now recognized to have seven
compartments (Wickham & Brown, 1998). Brown and his
colleagues (2007) later identified 19 compartments across
three shoulder muscles (pectoralis m., latissimus dorsi,
deltoid) and noted that compartments were coordinated
across muscles and that groupings of motor units across
neighboring muscles were formed as functional ―task
groups.‖
Compartmentalization of another sort is also seen in
series-fibered muscles. Muscle fibers in long muscles like
the sartorius generally extend from origin to insertion, but
not always. Some fibers terminate on connective tissue
within the belly of the muscle and do not go from origin to
insertion. This makes for a proximal and distal section of the
muscle, and histological studies have shown proximal and
distal innervation zones.
Accounting for compartmentalization during muscle
training remains uncertain. The multi-compartment rectus
abdominis provides an example of this uncertainty. Many
professionals advocate different exercises, such as crunches,
―V-ups,‖ leg raises, and incline sit-ups are necessary to train the entire
muscle. Research data do show that some exercises can have different
activation patterns, but not all researchers are convinced (Lehman &
McGill, 2001).
Intermuscular Coordination. Intermuscular coordination refers to
the actions of the muscles and limbs and other body segments working
31
together to produce efficient and purposeful movements in the context of
environmental and task demands. When we see a skilled dance
performance or an outstanding athlete in action we can easily recognize a
coordinated movement. The movements seem smooth, graceful, powerful,
and efficient. Movements may seem effortless without a lot of extraneous
actions. What we see and understand as a coordinated action is really a
precise patterning and role-playing of different muscles. Muscles are
designed for certain roles, which may change from one moment to the
next. Sometimes a muscle may function as an agonist, sometimes as a
stabilizer, sometimes as a neutralizer. As we see below, how a muscle is
controlled is largely dependent on what role it is playing at that moment.
Coordination Revealed
There may be rules governing the brain’s selection of coordination
features
Much is unknown about how the brain selects and activates
compartments along with other inter- and intramuscular coordination
factors, but emerging data from both humans and animals are beginning to
shed light on a few rules or
principles governing
coordination mechanisms.
These mechanisms can be
illustrated by examining the
calf muscles of humans and
cats. Calf muscles, comprised
of the triceps surae (soleus
and two-headed
gastrocnemious) and plantaris
all insert as part of the
Achilles tendon to produce
plantar flexion, but that may
be their only similarity. The
soleus is single joint and is
largely slow twitch, especially
in cats. The bi-articular
gastrocnemious tends to be
Example of MG and SOL forces and electromyographic (EMG)
more fast twitch, and has
activities for consecutive step cycles of uphill walking (60°) on a
walkway. Cats made a step or two at the bottom, level part of the
independent control within
walkway, then walked up the sloped part of the walkway, and
each head. The plantaris
finally performed a few more steps on the top, level part of the
walkway. From: Kaya et al. J. Exp. Biol. 206: 3645, 2003
32
muscle in humans has little force-generating capacity and probably serves
largely for proprioceptive purposes, but in the cat is a prime mover. The
entire calf group has been shown to activate differently depending on the
type of activity and respond differently to training. Walter Herzog and his
colleagues have done extensive work with cats by inserting EMG
electrodes into their muscles to determine muscle activation patterns and
inserting force gauges into the cat tendons to measure muscle force output.
These authors have found that force sharing among these muscles
differs dramatically dependent on the task. When standing still, the cat
soleus is active, wheras the gastrocnemous is minimally active. During
walking the gastrocnemious and soleus increase in activity, but as walking
becomes faster, or during uphill walking, the soleus activation increases
only moderately as the gastrocnemious activity rises markedly.
Furthermore, the force output of the soleus, even as EMG levels rise, stays
the same or decreases.
Both of these muscles are plantarflexor prime movers, so why is
there a difference in activation and force production? The authors‘
speculated that if the gastrocnemious was active during standing then knee
flexion would also occur, requiring quadriceps activity (knee extension) to
counter it. It may seem intuitive that the soleus is activated more during
standing because it is slow twitch, but this may be a minor reason. The
gastrocnemious also has slow twitch fibers, and because of its large size
probably has about the same number of slow twitch as the soleus. At a low
level of gastrocnemious contraction is likely only the slow twitch fibers
would be contracting.
Overall, during standing use of the soleus is more metabolically
efficient, but mostly because it is a single joint muscle and not because it
is mostly slow twitch. The gastrocnemious may maintain some level of
activity even during quiet standing in order to maintain readiness for
postural disturbances.
As the need for muscle force increases during uphill walking or
fast walking, the soleus does not keep up with an increasing level of
muscle activation or force output. The lack of an increase in soleus force is
probably due to the electromechanical properties of the muscle. At faster
velocities the contractile process cannot keep up due to force-velocity
relationships. The authors have concluded that control of the soleus is
much more dependent on intrinsic factors such as maintaining internal
muscle stiffness, whereas controlling the gastrocnemious is based on
extrinsic factors, such as maintaining plantar flexion force and speed. In
addition, during various phases of the gait cycle the biarticular
33
gastronemious acts sequentially or simultaneously as a plantar flexor and
as a knee flexor.
During the fastest movements in cats, which are paw shaking and
scratching, the soleus may go silent, while the gastrocnemius is highly
active. It is apparent from these movements that the soleus cannot keep up
with superfast cyclical contractions, and in fact, it might become a burden
and interfere with fast movements. These authors have also found that
during faster walking and running there is an increase in co-contraction
between soleus and tibialis anterior. The authors speculated that cocontraction stiffens the joint, which eventually might help in joint stability
or allow more efficient use of elastic energy.
Based on these and other data, these authors have concluded that
optimizing muscle activity is based on finding the most efficient metabolic
use; given the constraints of the system and the demands of the task. For
example, running fast is not metabolically efficient, but given the task
demands to run fast the "system" tries to organize itself to be metabolically
efficient. Conceptually this makes sense, but the experimental evidence for
this is hard to come by because it is so hard to measure, and there are other
researchers who do not agree with this suggestion that metabolic efficiency
is the primary ―rule‖ for organizing movements.
Muscle action is situation-dependent, which must underlie training
program principles
The important conclusion from these and other data are that the
actions of muscles are situation-dependent. Simply referring to textbooks
and similar sources to determine the actions of muscles provides an
incomplete, if not erroneous, view of the actions of muscles. A muscle‘s
inter- and intramuscular coordination is dependent on movement speed,
force needs, the number of joints being moved, muscle length, and joint
position. Further, is highly dependent on the outcome purpose of the
contraction, whether it is limb movement, postural stabilization, or any
number of other roles muscle contraction can play (Kornecki et al., 1998).
What are the implications of this for training? Though cat data
cannot be directly applied to humans, for illustrative purposes we can
gather some insight on how to prescribe training not based on muscle
activity but based on functional needs. Based on Herzog's data, doing
seated calf raises (soleus isolating exercise) would hamper development of
vertical jump performance. The reason for this is that a large slow soleus
muscle may get in the way of explosive plantar flexion actions.
34
There is human experimental evidence to support this suggestion.
Mackenzie et al. (1995) and Ng & Richardson (1990) have shown that
high speed training (with low or no external weight) may improve the
strength of the gastrocnemius but not the soleus. Mackenzie et al. even
found the soleus got weaker after high speed training, but according to the
Ng & Richardson study, this won't hamper vertical jump performance.
Similar types of results could be found for the hamstrings and quadriceps,
because it has been suggested that the hamstrings and rectus femoris are
movers whereas the vastii have a more stabilizing role (Richardson &
Bullock, 1986). These supporting and stabilizing muscles may not be as
active in high speed movements. In the upper arm Kulig et al. (2001)
found that during the lowering (eccentric) phase of arm curl exercises that
the brachialis and biceps brachii were activated differently depending on
the speed of movement. If the weight was lowered fast the biceps brachii
was more active, if the weight was lowered slow the brachialis more
active.
Other studies have looked more deeply at motor unit behavior as a
result of training. Van Cutsem et al. (1998) looked at ankle dorsiflexion
muscle activity following high speed (ballistic movements) strength
training. Strength and speed both increased. The size principle of motor
unit recruitment was maintained, but motor units fired earlier and with
faster firing rates after the training. That is, they had lower recruitment
thresholds. High speed force was initiated with very rapid firing rate at the
onset of high speed contractions and the force/speed was maintained by
increased use of doublets or triplets. Other authors have suggested that
much of these changes can be traced to changes in corticospinal and spinal
cord circuitry (Carroll et al., 2001, 2002, 2008).
Summary and Application
In this chapter we focused on the motor unit. Controlling a single
motor unit‘s firing behavior requires the coordination of thousands of
neurons, and controlling a purposeful muscle movement requires
controlling hundreds or thousands of neurons. It is a daunting task that is
made somewhat simpler by the use of rules. Coordinating motor unit
behavior (e.g., intramuscular coordination) or overall muscle and limb
movement (intermuscular coordination) is based on movement purpose,
and at least in some cases, metabolic efficiency.
The take home point is that we can use this as a guide to training.
Training, whether it is for rehabilitation or prevention, must take into
account specific task requirements so that the neuromuscular system can
35
organize itself to produce task-specific coordination patterns that
subsequently result in task-specific neurophysiological adaptations.
Simply exercising muscles based on movements the muscle is capable of
making will not produce highly coordinated actions or necessarily even
develop the muscles in manners they were intended to work.
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38
CHAPTER 3
NEUROMECHANICS
Chapter Outline
I. Mechanical Properties of Skeletal Muscle
II. The Muscle-Tendon Complex Modeled as a Machine
III. The Neuromechanical Machine at Work
IV. Summary and Application
Mechanical Properties of Skeletal Muscle
s we have seen in previous sections, the nervous system takes
into account properties of the muscle when activating the
muscle. Muscle properties like strength and fatigue are
factored into the brain‘s plan for movement. Not only that, but nervous
system activation purposefully modifies the mechanical characteristics of
the muscle-tendon complex. This relationship between the nervous system
and the functional mechanical properties of the muscle is called
neuromuscular mechanics (or simply neuromechanics).
In order to understand neuromechanics it is necessary to look at the
muscle-tendon complex not as an anatomical system, but rather, as a
mechanical work-producing machine. Each major anatomical component
of the muscle tendon complex can be identified as having mechanical
properties that contribute to the overall functioning of the muscle. The
nervous system then serves to control how these mechanical properties are
varied in order to meet the needs of movement.
A
The muscle-tendon complex has extensibility, elasticity, and contractility
Most all skeletal muscles are comprised of a central area of muscle
tissue with tendons on both ends. Connective tissue, namely the
epimysium, perimysium, and endomysium, run longitudinally throughout
the muscle tissue and merge at the ends to form the tendons. Muscle tissue
is an excitable tissue, meaning that it responds to electrical impulses.
Functionally, the muscle-tendon complex has three important mechanical
properties: (1) extensibility, its ability to stretch; (2) elasticity, the ability
to recoil from stretch; and (3) contractility, the ability to shorten to
39
produce force. Only muscle tissue has contractile properties, and it can
shorten about half its resting length. Though both muscle tissue and
connective tissue have extensibility and elasticity, muscle tissue has a
greater range of stretch and recoil, being able to stretch about 50% of its
resting length. Elongation capability is proportional to muscle length, and
inversely proportional to its cross-sectional area. Extensibility and
elasticity are less in the tendon tissue.
The Muscle-Tendon Complex Modeled as a Machine
The muscle machine has elastic, viscoelastic, and contractile elements
The functional properties of muscle and connective tissue work
like a machine. Together with the interstitial fluid that bathes the tissues,
the anatomical components of the muscle can be replaced with mechanical
components.
The first component of the muscle machine is the contractile
element (CE), made up from the muscle fiber. Specifically, it is the actin
and myosin sliding filaments in the sacromere that shorten to produce
force. The second component is the parallel elastic element (PEE), made
up of the connective tissue surrounding and
The conventional thought was that force from
the CE was transmitted to and through the
running parallel to the muscle fibers
series and elastic components to the bone.
(perimysium, epimysium, endomysium, and
While the tendons, of course, do this, the
mechanical properties of the epi- peri- and
fascia). The PEE acts like a spring that allows
endomysiums and fascia in transmitting and
the muscle to stretch when the muscle is
storing force is now under debate. A host of
externally stretched or when the CE contracts. other protein molecules and structures
(costameres, nebulon, connectin (titin),
The tissue‘s resistance to stretch is called its
dystrophin, focal adhesions, desmin, skelemin)
have been shown to provide connections within
stiffness. Tissues with a low resistance to
and outside of the sarcomeres and muscle
stretch are called compliant. When stretched,
fibers and transmit force (Patel and Lieber,
1997). In general, what this means is that the
force is stored, and when released provides a
forces produced by the contractile elements are
recoiling or restorative force. The stored force dispersed along most all the axes of the muscle
fiber, that is, from the inside of the muscle
is non-linear, that is, the more the elements
laterally across to the outside and
are stretched the harder and harder it becomes longitudinally from one end to the other end of
the muscle. These structures supposedly
to stretch them, and the more and more force
provide series and parallel elastic properties,
thus increasing the complexity of force
is stored.
transmission. To quote from Patel and Lieber
The third component is an elastic
(1997), "The path of force transmission from
the actomyosin complex to the tendinous
component lying in series with the muscle
insertion is poorly understood." For our
tissue. This series elastic component (SEE)
purposes then, we will not consider the actual
structures that make up the PEE and
is made up from the tendons and has the same anatomic
SEE, other than the tendon; only how the
functional characteristics of the parallel
whole muscle behaves.
elastic element.
40
The forth component is the fluid medium that surrounds the muscle
and connective tissue. This fluid, the viscous element (VE) provides
resistance to stretch and shortening and in doing so acts to dampen force.
In the diagram below the VE is modeled as a piston moving in and out of a
cylinder filled with fluid. Like a syringe, the piston can only move when
sufficient force is built up to push the fluid through a small opening. The
more viscous the fluid, the harder it is to push or pull the piston. The
dampening of force works like a shock absorber to smooth out contraction
force output, but beyond that the exact role the VE plays is largely
unknown.
The diagram below schematically illustrates the muscle elements.
When the CE contracts it must first build up force against the SEE, PEE,
and VE. The SEE and PEE stretch, and only when they have stored
sufficient force does the limb move. Hence, the CE does not instantly
move the limb when contracting. The delay between the time of
contraction and actual limb movement or force output of the limb is called
the electromechanical delay (EMD). Since the springs (SEE, PEE) and
the viscous element (VE) are not linear, the harder and faster the muscle
contracts, the more the spring tension and viscous element tension
increase. The overall functioning of the VE is not well understood, so we
will not include it in further discussion.
The Neuromechanical Machine at Work
The length-tension relationship reveals nervous system control of muscle
mechanics
The amount of isometric force a muscle can generate and store is
dependent in part on the length of the muscle. This relationship is modeled
as the length-tension curve and includes both contractile and elastic
elements. The length-tension curve thus has three parts; an active curve
41
Tension
Short: too much overlap
and binding overlap
e
ti v
Resting Length:
optimal overlap
ac
based on contractile elements, a passive
curve based on elastic elements, and an
ov
max
era
ll
overall curve that is the sum of adding the
active and passive components.
The active portion curve is based
ive
on the amount of overlap of the actinss
pa
myosin filaments. The filaments form the
0
sarcomere, which is the force-generating
150
0
50
100
unit of the contractile element. The
% of Resting Length
diagram illustrates that when the muscle is
short the filaments are grossly overlapped
and when the muscle is long there is not enough overlap. Too much or too
little overlap results in unavailability of actin-myosin binding sites and
thus fewer cross-bridge formations. Fewer crossbridges result in less
force. An optimal amount of overlap enables full crossbridge formation
and is just longer than resting length.
Long: less overlap
The passive portion of the curve is non-linear due to the nature of
the connective tissue. At longer stretches a large amount of force can be
stored in the elastic element. This passive tension is stored and provides a
recoiling force when released.
The separation of the contractile and elastic elements in the lengthtension curve hides the complexity of this system in action. For example,
a stretched muscle does not necessarily mean that the elastic and
contractile elements are both stretched. Consider a high force contraction
against a very heavy load. As the force is increased the contractile element
shortens and the elastic element stretches. At this point there is no
movement because the shortening of the contractile element is countered
by the lengthening of the elastic element. When enough contractile force is
generated and transmitted to the elastic element the load will move. As the
limb begins to move the contractile element will shorten, but the elastic
tissue will likely remain elongated.
In the figure below are length-tension curves of the medial
gastrocnemius muscle-tendon complex during various activities. Note that
the shortening and lengthening behavior of the muscle and the tendon
200
42
differ between different types of contractions. How can this done under
normal circumstances?
Changes in length of
fascicle and tendinous
tissues during various
human movements. DF,
dorsiflexion; PF, plantar
flexion; Lf, length of
fascicle; Lt, length of
tendinous tissues.
Fukunaga et al., Exerc.
Sport Sci. Rev., 30: 106110, 2002.
The key to getting a large amount of muscle force or an efficient
production of force is to have the contractile element near resting length
and the elastic element stretched. In the graph below of the medial
gastrocnemius muscle, note that ankle bending, jumping, and walking are
in a good length-tension position throughout the important points of the
movement. The contractile element can stay at near the same length
(quasi-isometric) because the elastic
element is lengthening and the muscle is
involved in a two-joint action.
Length-force relation of sarcomere during ankle
bending, jumping, walking, and pedaling. Fukunaga
et al., Exerc. Sport Sci. Rev., 30: 106-110, 2002.
Movements like walking, vertical jumping, and squatting take
advantage of the favorable length-tension relationship properties afforded
by multijoint muscles. These movements are called concurrent
movements. In a concurrent movement a multijoint muscle is contractile
shortening on one joint to move a load, and at another joint is being
43
Tri
c
Su ep s
r ae
stretched. This enables the muscle tissue to maintain a quasi-isometric
length. As the figures illustrate, the quasi-static portion of the movement
occurs during the important force producing part of the movement,
implying that the nervous system must control the muscle activation level
and movement of the surrounding joints to maintain the favorable length
tension curve.
Sometimes the arrangement of
multijoint muscles leads to a lengthtension disadvantage. Most biarticular
Qua
ds
(or multiarticular) muscles are not long hip extens ion
Ha m
enough to permit full range of motion
strin
gs
knee extens ion
at the same time of both joints. For
example, flexing the hip and extending
plantarflexion
the knee at the same time are a result of
rectus femoris shortening at both joints.
This shortening is rapid and pronounced, causing the rectus femoris length
and shortening velocity to quickly get into the unfavorable areas of the
length-tension-velocity curve. At the same time the hamstrings are
lengthening at both joints, thus the elastic tension rises rapidly and may
reach a point where full range of motion of hip flexion and knee extension
is prohibited (and sometimes painful!). This type of movement is referred
to as countercurrent.
The nervous system also wants to limit muscle shortening velocity
In a concentric contraction
the shortening muscle loses force
generating capabilities as the speed
max
of shortening increases. This is due
Tension
to inefficient coupling of the actinmyosin crossbridges and greater fluid
viscosity at higher speeds. The cross0
bridges need time to connect and the
fast
0 slow
less time available the fewer crossEccentric Velocity
Concentric Velocity
bridges will form. The relationship
Isometric
between contraction velocity and
= point of peak power
force output forms the force-velocity
curve. In the illustration note that at
maximal speeds the force output is
very low, and maximum force is produced during an isometric and
eccentric contractions. The shape of the eccentric portion of the force
44
eccentric
sh
0
100%
% of max velocity
Other Musculoskeletal Properties Influencing Nervous System
Control
The nervous system takes into account mechanical factors such as
muscle length, velocity, and stretch. It also takes into account the fiber
type distribution, anatomical arrangement of the muscle fibers (e.g.,
fusiform versus pennate), muscle size and fiber length, tendon length and
thickness, and biomechanical musculoskeletal characteristics. The
influence of these characteristics on movement production is summarized
below in the table.
Tendon length, thickness,
and morphology
Moment arm
Fiber type
Muscle fiber area
Long tendon increases the range of muscle, increases dampening
and energy storage. Thicker tendons are stiffer and more resistant
to stretching, thus tend to transmit force quicker and with less
force storage. The proportions and arrangements of the collagen,
reticular, and elastic fibers give the connective tissues its
functional properties as well as strength.
Long moment arm enables more force. Short moment enables
increased speed and ROM
Fast twitch enables fast and power contractions, slow twitch and
slow twitch provides fatigue resistance.
Large fiber cross-sectional area enables increased force
production.
rc
0
sa
or
t
om
er
e
Lo
len
gt
h
lon
g
tension (% of max)
velocity curve is highly variable depending on factors such a training
status and muscle tested, and will not be discussed further. It is clear that a
high shortening velocity is an inefficient use of the contractile machinery.
Under normal circumstances the nervous system tries to avoid these
movements, and does so in the same way it controls the length-tension
curve.
Of course the length-tension and force-velocity properties of the
muscle cannot be separated. The length-tension-velocity curve below
illustrates that muscle tension is low if velocity is high, regardless of
muscle length. At low concentric
100%
velocities muscle length is the
important tension modulator.
45
Muscle fiber length and
fiber arrangement
Long fibers provide increased speed and increased range of
motion. This does not necessarily mean that a long muscle has
long fibers. But in general, a longitudinal muscle will have longer
fibers than a pennate muscle, and a pennate muscle will have a
larger cross-sectional area. Obliquely arranged muscle fibers may
also provide force vectors different from longitudinal muscles.
The muscle’s role in movement influences movement control
Muscles contract in order to produce force, but that force may be
used in numerous ways other than to move a body part. How that force can
and will be used is largely dependent on the purpose of movement, and is a
key outcome of coordination strategies.
Muscles directly involved in producing the desired movement are
agonists. Agonists can be either prime movers or synergists. Antagonist
muscles oppose the action of the agonists. Other muscles have an indirect,
but vital role in movement. Fixators and stabilizers usually contract
statically to stabilize a body part against the pull of contracting muscles.
Many of these muscles are categorized as postural muscles. Neutralizers
act to prevent an undesired action of one of the agonists. It is important to
understand that at any given moment the same muscle may act as an
agonist, stabilizer, neutralizer, or even antagonist. Agonist and antagonist
muscles may work together as synergists. All of these roles – to move, to
stabilize, to neutralize, to oppose – require the muscle to contract in a
different manner and require a different coordination scheme.
For example, antagonist muscles must be controlled alongside the
agonist, either by inhibition or co-contraction. It is generally desirable to
have the antagonists inhibited (relaxed) during agonist action. This allows
the agonist muscle to exert a full amount of joint torque and increases
overall metabolic efficiency. Although antagonist quiescence during
agonist action appears to be desirable, often times the contraction of the
antagonists during agonist action (cocontraction) is desirable.
Cocontraction can help stabilize the joint, especially during very rapid or
very forceful agonist contractions.
Cocontraction of the antagonist is also used to moderate the force
output of the agonist, particularly in movements where accuracy
predominates over speed. As a result of training or practice, such cocontraction is usually reduced. In the example below of a rapid forearm
flexion with a quick stop, EMG records of the biceps b. and triceps b.
muscles during unpracticed and practiced movements are shown. The
biceps b. flexes the limb and the triceps b. stops the limb movement. Note
46
the amount of electrical activity overlap (co-contraction) in the unpracticed
situation and how the muscles fire in much more discrete bursts in the
practiced condition.
Rapid forearm flexion with quick stop:
Unpracticed movement
Rapid forearm flexion with quick stop:
Practiced movement
biceps b.
biceps b.
triceps b.
triceps b.
Neuromechanics in action
The mechanical muscle model is important because it enables us to
examine what the nervous system is trying to control. In other words,
changing the mechanical properties results in movement. Consider the
figure below of a simple one joint system with an agonist muscle (biceps
b.) on one side and an antagonist (triceps b.) on the other. The joint
system is modeled as only a contractile element with a simple elastic
spring – no viscous element. When the biceps contracts it stretches the
spring, which is nothing more than increasing the spring's stiffness.
Relaxation of the triceps' contractile element reduces stiffness. In order
for our arm model to do a flexion movement, the stiffness of the agonist
(biceps) is increased and the stiffness of the antagonist (triceps) is
maintained or not increased to the same amount as the biceps. The
nervous system may inhibit the
triceps to decrease its neural
activation. Of course, as the limb
begins to flex, the triceps is
stretched, which causes it to
increase its passive and overall
stiffness (which, actually, is not
that much in a normal ROM
movement). The stiffness of both
muscles must be continually
altered to get the limb to its
desired point. The way the
springs move the limb is called
47
the mass-spring model: mass refers to the amount of load (limb plus
external weight) the springs must overcome. Thus, if you want to do a
flexion movement you must unbalance the stiffness of the biceps and
triceps muscles in favor of increasing biceps stiffness. This all suggests
that the nervous system knows how much or how little stiffness to put into
each muscle in order to control limb force, speed, and position.
The Stretch-Shorten Cycle
If a muscle is stretched rapidly prior to concentric contraction then
it can produce more force. This phenomenon is called an eccentricconcentric contraction or the stretch-shorten movement, and is readily seen
in a windup or a counter-movement action. Many common activities, like
running, jumping, and throwing are movements of this type. It takes
advantage of a phenomenon called the stretch-shorten cycle (SSC).
Exactly why the force can be increased is not fully known, and several
theories have been proposed. Regardless, this method is most effective if
the countermovement is not passive, but is an active eccentric contraction,
that is, the muscle being stretched is being activated at the same time. The
theories behind the stretch shorten cycle include (1) release of stored
elastic energy, (2) the preload effect, (3) excitation of reflex mechanisms,
and (4) making available more time for contraction.
The stretch shorten cycle stores and releases elastic energy
The most commonly cited reason for stretch-shorten cycle
enhancement is that it takes advantage of the stored elastic energy to
enable more forceful contractions. The amount of stored energy is based
largely on stretch velocity, and somewhat on the length of the stretch. The
faster the velocity, the more stored energy, and the quicker the transition
from stretch to shorten (or eccentric to concentric), the more stored energy
is released.
The stretch shorten cycle may conserve ATP for later use
The stretch-shorten may make available more chemical energy
(i.e., ATP) in a phenomenon called the preload effect. This is simply the
fact that the contraction starts at a higher level of force (due to the
eccentric contraction), and this spares available chemical energy. Force
can now increase from a higher baseline value and take advantage of more
48
available chemical energy. There is not much empirical evidence to
support this theory.
The stretch shorten cycle may cause muscle facilitation through reflexes
The stretch portion of the stretch shorten cycle may cause the
muscle spindles to be excited, thus facilitating the muscle to contract
stronger and with a faster rate of tension development. By doing this, not
only is the power of the contraction increased, but the eccentric to
concentric contraction coupling time is reduced, which increases the
storage and use of elastic energy. There is some experimental evidence for
this effect, but it is not a consistent finding.
Continued SSC contractions (e.g., endurance running) may cause
the elastic components to get compliant, which then may lead to a
reduction in reflex gain, which in turn may lead to a lack of reflex
potentiation of the SSC movement (Avela & Komi, 1998). Avela et al.
(1999) later showed that repeated passive stretching also reduced reflex
sensitivity, further supporting the idea that repeated stretch may make
more compliant the mechanical properties of the muscle/tendon unit or the
spindle itself and in so doing reducing reflex augmentation.
The stretch shorten cycle creates a longer time for contraction
Recent evidence has suggested that the most important factor in the
stretch shorten cycle is that the eccentric contraction of a muscle prior to
its concentric phase enables the muscle to contract for a longer period of
time, thereby providing sufficient time to build force.
Exercise Training and Mechanical Properties
Some exercise training modes have a direct impact on the muscle
mechanical system. Flexibility training (stretching), in particular, is
specifically designed to reduce the elastic stiffness of the muscle tendon
complex. Hypertrophied musculotendinous tissue also affects stiffness, but
not to the same extent. The implications of these training induced changes
are described below.
Flexibility training mechanisms are largely unknown
Flexibility exercises as typically done are intended to increase joint
range of motion (ROM). A single stretching exercise session may lead to
49
transient increases in ROM, and a long term program may result in chronic
increased in ROM. An increased joint ROM may result from (1) decreased
stiffness of the muscle-tendon complex, (2) a longer muscle tendon
complex, (3) more pain tolerance to stretching, or (4) relaxation of the
contractile element. Surprisingly, very little is known about what actually
happens in humans.
Animal studies reveal that the effects of long-term stretching may
increase muscle length by adding sarcomeres and/or add length to the
tendon (Taylor et al.1990; Noonan et al., 1993). The viscoelastic
properties of the muscle-tendon unit may be little affected. What happens
in humans with normal stretching programs is unknown. Some
investigators, though, have provided good evidence that the improvement
in chronic ROM from a stretching program may be due to an increased
pain tolerance to stretch and has little to do with changes in the muscle
itself (e.g., Magnusson et al., 1996). Increased tolerance may be a purely a
psychological adaptation or could be due to changes in sensory outflow
from the muscle, though Weppler and Magnusson (2010) have proposed
solid rationale that a reduction in sensory outflow and a reduction in pain
signaling is the primary reason.
On the other hand, the acute effects of stretching may be to alter
the viscoelastic properties. In this case the muscle becomes more
compliant, perhaps through changes in the intramuscular collagen. Several
studies have shown that to get a lasting effect each muscle must be
stretched for more that 45 seconds for more that 3 repetitions; upwards to
7.5 minutes of stretch per muscle (5 sets at 90s per set; Magnusson et al.,
1996). At 7.5 minutes per muscle the effects lasted less than 1 hour. With
less rigorous stretching the increased tissue compliance dissipates quickly.
Magnusson et al. (2000) showed that the reduced stiffness seen after a 45 s
stretch returned to normal before the next stretch that happened 30 s later.
Others have shown that somewhat more rigorous stretching may have
effects lasting only 10 minutes (Magnusson et al., 1998).
Stretching has little impact on injury prevention or performance
The lack of a definitive mechanism for stretching effects, coupled
with evidence for rather transient effects, raises the question of the
usefulness of stretching exercises. Indeed, a large amount of research over
the past 15 years has demonstrated that stretching before strength and
power performance reduces performance, and stretching to reduce injuries
has not been demonstrated. Many of these studies are difficult to translate
to real world situations because the stretching far exceeds what is normally
50
done prior to exercise, and that the subsequent exercise trials follow much
too soon. For example, Taylor et al. (2009) noted that when static
stretching was followed by sport-specific warm ups the negative effects of
stretching were eliminated. In addition, static versus ballistic stretching
may produce different results. Nevertheless, these studies give insight to
how changes in the mechanical properties of the muscle influence
movement.
Reduced musculotendinous stiffness following an acute stretching
bout is suggested to reduce the transmission of force through the system. A
compliant musculotendinous system is suggested to absorb and dissipate
force rather than transmit it. In addition, a compliant system alters the
production of force because of changes in the length-tension-velocity
conditions. With a compliant system the muscle will contract rapidly and
shorten to a large degree prior to the elastic elements becoming stiff
enough to transmit the forces to the bone. Thus, at the point of time the
force can be transmitted, the sarcomeres are short and moving rapidly —
both of which limit force production. An additional suggestion is that
inhibitory reflexive pathways are excited, or facilitory pathways inhibited,
by the stretch.
Data regarding stretching and injury prevention is less clear and
much more difficult to gather (Schilling & Stone, 2000). However, in an
excellent review by Gleim and McHugh (1997), these authors stated that,
". . . we see no strong evidence proving that flexibility or stretching is
associated with rates of strains, sprains, or overuse injuries that can
applied across all sports or levels of competition . . . we may never know
the true relationship between flexibility and injury."
Hypertrophied tissues generally increase stiffness
Tissue stiffness is dependent on the morphological and
histochemical makeup on the tissue fibers, health of the tissue, the length
of the tissue, and the thickness of the tissue. Typical stretching as
described above may alter the morphological tissue characteristics or the
length of the tissue to increase compliance. Hypertrophied muscle and
tendon tissue, such as the result of a resistance training program, increases
stiffness by increasing tissue thickness and perhaps tissue density. These
changes in stiffness may be small, and may be balanced out by stretching
exercises.
51
Summary and Application
The mechanical properties of the muscle tendon complex,
including its contractile characteristics, elasticity, and extensibility, are
important factors in how the nervous system controls muscle force output
and movements. The nervous system must take these properties into
account, and even purposefully modify them, to produce efficient and
effective movements.
Exercise training influences the mechanical characteristics of the
muscle tendon complex, and some laboratory evidence suggests that
performance in strength and power activities may be hampered by
stretching activities that increase compliance in the muscle tendon
complex. On the other hand, other evidence suggests that the nervous
system modifies its activation to control for changes in these mechanical
properties, particularly if the stretching activities are not excessive. Taken
as a whole, it appears that exercise training such as stretching to increase
elasticity or resistance training to increase stiffness, are necessary
interventions to enhance muscle tendon health.
Bibliography and Other Sources
Avela, J. J., & Komi, P. V. (1998). Reduced stretch reflex sensitivity and
muscle stiffness after long lasting stretch shortening cycle exercise
European Journal of Applied Physiology, 78(5), 403-410.
Avela, J. J., Kyrolainen, H. H., & Komi, P. V. (1999). Altered reflex
sensitivity after repeated and prolonged passive muscle stretching.
Journal of Applied Physiology, 86(4), 1283-1291.
Fukunaga, T. T., Kawakami, Y. Y., Kubo, K. K., & Kanehisa, H. H.
(2002). Muscle and tendon interaction during human movements.
Exercise & Sport Sciences Reviews, 30(3), 106-110.
Gleim, G. W., & McHugh, M. P. (1997). Flexibility and its effects on
sports injury and performance. Sports Medicine, 24(5), 289-299.
Herda, T. J., Cramer, J. T., Ryan, E. D., McHugh, M. P., & Stout, J. R.
(2008). Acute effects o static versus dynamic stretching on
isometric peak torque, electromyography, and mechanomyography
of the biceps femoris muscle. Journal of Strength & Conditioning
Research, 22(3), 809-817.
Magnusson SP, Simonsen EB, Aagaard P, et al. (1995). Viscoelastic
response to repeated static stretching in the human hamstring
muscle. Scand J Med Sci Sports. 5: 342–347.
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Magnusson SP, Simonsen EB, Aagaard P, Kjaer M. Biomechanical
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Am J Sports Med. 1996;24: 622–628.
Magnusson, S. P., Aagaard, P. P., & Nielson, J. J. (2000). Passive energy
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Magnusson, S. P., Aagard, P. P., Simonsen, E. E., & Bojsen-Moller, F. F.
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53
CHAPTER 4
MOVEMENT PRODUCTION
Chapter Outline
I. Motor and Sensory Systems and Reflex Movements
II. Central Nervous Systems Initiation and Control of Movement
III. Summary and Application
Motor and Sensory Systems and Reflex Movement
p to now we have seen that the basic unit of movement (i.e.,
the motor unit) is controlled in many ways to get changes in
force and speed and even movement direction. But we do not
have a good idea of what gets the motor units active, or put differently,
what provides the controlling influences. What makes a motor unit fire at a
faster rate, or causes recruitment of more motor units? Why or how is one
muscle compartment recruited when another is not? In order to answer
these questions we need to take a look at the nervous system and how it
works to activate muscle. First, we will look at the way reflexes work, as
they are the simplest, then we will add in voluntary control and the
integration of both.
U
Sensory receptors initiate reflex movements
By definition, reflexes are non-voluntary movements initiated by a
sensory stimulus. We will only consider somatic reflexes controlled by the
motor system and not visceral reflexes controlled by the autonomic
nervous system. Each somatic reflex has a sensory ending to detect and
transduce a stimulus, a sensory neuron to transmit the signal, an
integrating center like the spinal cord to encode and relay the signal, a
motor neuron to transmit the signal to the effector organ, and an effector
organ. The effector organ is, of course, muscle. The simplest reflex
pathway, the stretch reflex, provides a basic illustration on how reflexes
work.
In a stretch reflex a stretch stimulus is detected by a muscle spindle
sensory ending, the muscle spindle transduces the mechanical stimulus to
a bioelectric signal, the signal is sent via sensory neurons to the dorsal
54
horn of the spinal cord where it synapses with a motor neuron going to the
same muscle that was stretched. The motor neuron is activated and
subsequently, initiates a contraction in the muscle that originated the
stretch signal. This monosynaptic reflex loop is a component of many of
our movement processes, as are reflex loops that are much more complex.
At the peripheral end of a sensory neuron is a sensory ending,
otherwise known as a receptor. Receptors are special organelles designed
to detect stimuli from the environment and translate that stimuli into
electrical signals the nervous system can understand. It is only through
sensory endings that we become aware of the world around us and the
world within our own body. Receptors come in many forms and can be
classified according to several classification schemes. Two main
classification schemes are location and type of stimulus detected. Receptor
location can be broadly classified as within the viscera (internoreceptors
or visceroreceptors) or external to the viscera (externoreceptors or
somatoreceptors). Internoreceptors generally detect stimuli from within
the body and largely serve to feed information back to the CNS regarding
basic physiological processes, such as core temperature, acid balance, and
smooth muscle movement. Most externoreceptors are located in the
musculoskeletal system, and while they provide information on the
internal environment, they also detect the external environment and the
body‘s actions within the external environment.
Receptors detect numerous types of stimuli and are classified based
on these stimuli. Thermoreceptors (temperature), chemoreceptors
(chemical and pH), baroreceptors (fluid pressure), photoreceptors (light),
olfactory receptors (smell), taste receptors, auditory receptors (sound),
mechanoreceptors (mechanical disturbances), and nocioreceptors (pain)
are located throughout the body. Proprioceptors are specific types of
mechanoreceptors designed to detect movement within the
musculoskeletal system, and as such, play a vast role in motor behavior.
Proprioceptors of many types are located in many tissues
Proprioceptors are somatoreceptors feeding information to the
CNS on bodily movement, including the amount and direction of
movement, rate of movement change, and forces. This information is
processed by the CNS and gives rise to kinesthesia, the conscious and
subconscious awareness of body and limb positioning and movement in
space. In addition to providing movement feedback, proprioceptors
directly or indirectly initiate skeletal muscle reflex actions, and because of
55
their locations, some provide information regarding tissue homeostatis to
the CNS.
Proprioceptors are located in muscles, tendons, ligaments, skin,
and numerous other tissues, particularly tissues surrounding joints. Each of
these tissues can contain different types of proprioceptors, each
proprioceptor supplying a different amount and type of information. Some
proprioceptors have nerve endings contained within bulbous tissue
corpuscles, surrounding tissues masses, or are free endings intertwined
among tissue. The type of stimulus and how a sensory ending responds to
that stimulus is dependent on the organization of the tissue and nerve
endings. Some endings may respond to rapid stretch, some to slow
sustained pressure, some to shear forces, some to direct pressure. Sensory
endings in the inner ear, called the vestibular apparatus, are a special
form of proprioceptor not classified as somatoreceptors.
Mechanical stimuli to proprioceptors elicit generator potentials in
the receptor membrane, and if strong enough, forms action potentials. The
firing rate of action potentials is directly related to the strength of the
stimuli. Receptor sensitivity is the ability of a receptor to detect or
discriminate a stimulus. Low sensitivity means that it takes a large
stimulus to elicit a response from the receptor, or that small changes in
stimulus strength are not detected. Receptor acuity is similar to sensitivity,
but generally refers to groups of receptors working together. Many
receptors packed densely together, each with a small receptive field,
enable a finer discrimination of stimuli than fewer receptors with larger
receptive fields.
Though sensory endings in nearly every type of tissue can provide
some level of movement information, there are four types of
proprioceptors that are most important. These are muscle spindles, Golgi
tendon organs, joint kinesthetic receptors, and the vestibular apparatus.
The muscle spindle is a complex and controllable sensory organ
Muscle spindles are relatively large receptors located throughout a
muscle, though generally concentrated in the muscle belly. The function of
the muscle spindle is to detect muscle stretch and contraction
characteristics in order to provide muscle functioning feedback to the CNS
and to initiate a stretch reflex, also called a myotatic reflex. Both of these
functions are critical in the production of coordinated movement. The
seemingly simple function to detect muscle stretch hides the fact that the
spindle is a highly complex sensory organ that is second only to the eye‘s
photoreceptors in sophistication. The eye and muscle spindle are the only
56
sensory organs that can be directly controlled by the nervous system to
influence their sensitivity and acuity.
The spindle sensory endings are contained within a spindle-shaped
(fusiform) connective tissue capsule. Stretched end to end within the
capsule are specialized muscle fibers called intrafusal or fusimotor
fibers. Intrafusal fibers differ from the surrounding extrafusal skeletal
muscle by size and by the arrangement of muscle and connective tissues.
Whereas skeletal muscle is arranged in series as tendon, muscle tissue, and
tendon, intrafusal fibers are arranged in series as muscle tissue, tendon,
and muscle tissue. The central tendinous area of the intrafusal fibers
contains small gelatinous bags arranged in two basic forms. In nuclear
chain fibers the bags are laid out in series like a chain, in nuclear bag
fibers the bags are densely packed forming a bulbous middle section.
Two types of sensory endings innervate the spindle. Annulospiral
endings, with type Ia afferent neurons, wrap around the central area of the
nuclear chain and nuclear bag fibers. Flower spray endings, with type
spII afferent fibers, spread out along the intrafusal muscle portion of the
intrafusal fibers, primarily the nuclear chain fibers. The flower spray and
annulospiral endings both respond to stretch, but the arrangement and
location of the endings together with the arrangement of the nuclear bags,
results in different response patterns to the stretch. The varied
arrangement of the endings allows for the spindle to be sensitive to rapid
and phasic stretches, slow sustained and tonic stretches, stretch velocity,
static position, and perhaps stretch force. It is important to note that
muscle spindle morphology, including the presence of both nuclear bag
and nuclear chain fibers and sensory endings arrangement, can markedly
differ from one muscle or muscle region to another, giving each muscle
spindle a particular specialization.
What makes the spindle different from other sensory organs is the
ability of the CNS to control spindle function by contracting or relaxing
the intrafusal muscle fibers. Gamma motor neurons innervate the
Ia afferents
gamma efferents
nuclear bag
spII
afferents
intrafusal fibers
nuclear chain
57
intrafusal fibers on both sides of the central bag region. These neurons are
separate from the alpha motor neurons that innervate the extrafusal
skeletal muscle surrounding the spindles. Some muscles spindles have
beta motor neurons that innervate both intrafusal and extrafusal fibers.
The muscle spindle responds to both passive stretch and active contraction
Passive stretch to the surrounding extrafusal muscle tissue also
stretches the spindle capsule and subsequently, the intrafusal fibers. As the
intrafusal fibers lengthen the annulospiral and flow spray endings both
spread out. This distortion causes disturbances to the endings‘ cellular
membrane, which initiates the formation of generator potentials and if
strong enough, action potentials. With longer stretch and faster stretch
more action potentials are initiated. Depending on the stretch
characteristics the annulospiral or flower spray endings may become more
gamma efferents
excited. Through the Ia and/or spII
afferent neurons, the stretch
Ia afferents
information is fed back to the
spinal cord, where connections are
made initiating a contraction in the spII afferents
homonymous muscle, otherwise
known as the stretch reflex.
A. “Resting” State
Understanding the function
of a muscle spindle during an
active contraction is more
challenging. When the extrafusal
muscle contracts, it shortens. This
B. Passive Stretch
shortening would theoretically
cause the muscle spindle to shorten
and go slack, thereby removing any
stretch disturbances to the sensory
endings and causing the spindle to
go inactive. This would limit the
functionality of the spindle when
C. Active Contraction
the muscle shortens. However, this
does not happen. During shortening contractions the intrafusal fibers are
contracted via gamma motor neurons alongside the extrafusal fibers. This
phenomenon is known as alpha-gamma linkage. The shortening of the
intrafusal fibers on both ends of the center nuclear bag system stretches
out the center section even as the whole muscle is shortening. Put
differently, during a contraction the intrafusal fibers shorten and the center
58
section lengthens or stays the same length. Because the intrafusal fibers
mimic to some extent the shortening of the extrafusal fibers, the brain can
get feedback on overall muscle length and shortening mechanics. Further,
because the feedback coming from annulospiral and flower spray endings
differs depending on the muscle activity (eccentric contraction, concentric
contraction, passive stretch), the brain can interpret these signals and
accurately interpret contraction characteristics.
The CNS can control muscle spindle sensitivity and signal routing
The brain‘s ability to activate the intrafusal fibers enables it to set
the sensitivity of the spindle, also
known as gamma bias or reflex
gain. Low level contraction of the
intrafusal muscles tighten up the
intrafusal fibers and the center
section of nuclear bags, resulting in
sub-threshold generator potentials
or even slight afferent output.
Either way, the spindle is primed
and ready to respond to even the
slightest stretch, and will respond
strongly to even a moderate stretch.
On the other hand, the brain may
reduce spindle sensitivity by
inhibiting gamma motor neurons.
The stretch reflex response
in the homonymous muscle is not
the only function of the muscle
spindle, nor is it as simple as reflex
arc diagrams illustrate. Muscle
spindle activity is ongoing and
plays a direct or indirect role in
nearly every movement we make.
Some movements, like a windup before a throw, may make direct use of a
strong phasic response. Spindle activity in other movements may need to
be inhibited. Synergists are also facilitated and antagonist muscles are
inhibited through a process called reciprocal inhibition. Inhibition is
generally the result of the afferent signal being routed through Ia
inhibitory interneurons within the spinal cord. On the contralateral limb
there may be an opposite effect on the agonists (inhibited) and antagonists
59
(facilitated), or even distal effects. For example, spindle activity in the
soleus may inhibit activity of the quadriceps. This is a complex neural
circuit involving may type of interneurons, but it is likely initiated by the
standard stretch reflex (Iles and Pardoe, 1999).
High velocity stretches, such as that elicited by the classic tendon
tap medical procedure, produces a phasic response. This response is
strong and rapid, such as the knee jerk following the tendon tap. Slow
stretches, like postural sway, produce a tonic response. The tonic response
is slow and sustained and often occurs in extensor and postural muscles
and are thus is often called a postural or antigravity reflex.
The muscle spindle response is influenced by peripheral and central
factors
The strength of the spindle response is mediated by many factors,
both peripheral and central. Peripheral muscle factors include the prior
amount of muscle activity (called activation history), the type of activity,
and the muscle length are just a few factors that influence the strength of
the stretch reflex and the corresponding reciprocal inhibition. At the spinal
cord the complex neural circuitry is used to control the expression of the
reflex and reciprocal inhibition. For example, if the ankle dorsiflexors are
fatigued then the strength of reciprocal inhibition arising from dorsiflexor
spindle activity is increased, potentially making a strong contraction of the
soleus and gastrocnemious more difficult (Sato et al., 1999). Different
tasks may alter the amount of reciprocal inhibition. For example, the
amount of reciprocal inhibition in the
soleus induced by a contraction of the
tibialis anterior is stronger during
hopping and walking than standing,
even when the strength of tibialis
anterior contraction is the same (Lavoie
et al., 1997).
Prior training, experience, and
biological health may result in different
patterns of spindle response. Elders and
young often have very different reflex
responses (Chalmers & Knutzen, 2000).
Hoffman and Koceja (1995) showed
that stretch reflex gain is modulated by
other afferent inputs, in their case visual
and somatosensory. In particular, with
60
no vision or with unstable support surfaces, the reflex gain was reduced.
With no vision and with unstable surfaces, the authors maintained that
supraspinal inputs presynaptically inhibited the stretch reflexes in order to
have more central control over posture. An alternative explanation is that
more cutaneous inputs from the feet could inhibit the reflex.
The importance of supraspinal modulation is also seen in persons
with brain damage, as from a stroke. Under 'normal' conditions the brain
tends to inhibit the reflex. When the brain is damaged it may not longer
inhibit the constant stretch reflex activity. When this happens the stretch
reflex remains constantly active and the agonist muscle stays in a state of
spastic contraction. Because the antagonist muscle is also without
supraspinal inhibition of its stretch reflex, the result can be two
antogonistic muscles both being active and a state of rigidity.
The overarching point is that the stretch reflex is far more than the
knee jerk reflex. Muscle spindles are constantly at work, and the strength
of the reflex action (including reciprocal inhibition) relies on more than
simply the amount of stretch or amount of contraction of the agonist
muscle. The reflex characteristics, including proximal and distal facilitory
and inhibitory effects, are influenced by other reflex circuits and controlled
by supraspinal centers to match the needs of the task.
Golgi tendon organs (GTO) and the tendon reflex oppose the muscle
spindle response . . . sometimes
Golgi tendon organs are free sensory endings intertwined within
tendon fascicles and in series with the muscle fibers. During stretch to the
tendon the endings distort in a manner consistent with the stretch.
Tendons, as opposed to muscle tissue, are very resistant to stretch and
require a large amount of force to lengthen. Because of this the tendon
organ is said to act like a force detector more so than a movement detector.
However, current research suggests that the tendon organ can respond to
small forces.
Neuronal circuitry and early experimental evidence generally
reinforces the belief that stimulation of the tendon organ via contraction of
the muscle or external forces results in inhibition of the homonymous
muscle and its synergists, and facilitates contraction of the antagonist
muscle and its synergists. Notice that this Golgi tendon reflex circuitry
does not result in a contraction of the effector organ, and in fact, is said to
limit contraction force in order the protect the muscle and joints.
In a review by Chalmers (2002) it was noted that tendon organ
effects are much more complex than initially believed, having both
61
inhibitory and facilitory effects depending on the movement behavior,
contraction type, stretch type (e.g., active versus passive), and type of
muscle involved, such as flexors versus extensors. That the GTO can have
opposite influences, even on the same muscle, demonstrates supraspinal
influence over reflex
activity.
The tendon
reflex and the stretch
reflex are activated by
the same stimuli but
generally have opposing
effects. This raises the
question of which
reflex will emerge, that
is, which muscles will
be facilitated, and
which will be inhibited? Do they cancel one another out? This paradox is
seen throughout the nervous system and seems to reveal design
inefficiencies. Upon closer inspections, we see it reflects a sophisticated
design enabling supraspinal systems to control automatic movement
behaviors in numerous ways. For example, it appears that during novel
and high force movements, especially with untrained persons, the tendon
organ inhibitory actions override the spindle reflexes to keep the
musculoskeletal framework within safety limits. As a consequence of
training or experience, it appears that the tendon reflex is inhibited by
supraspinal centers, enabling full facilitation by the spindles.
Joint and skin proprioceptors often inhibit muscle contraction
Within joint tissues and in the skin surrounding most joints are
four to five different types of receptors. Those in the joints are specifically
referred to as joint kinesthetic receptors. The skin receptors are not
classically considered to be proprioceptors, but they do offer movement
related information and are thus considered here to function in part as
proprioceptors.
Among the receptor types are Pacinian corpuscles found beneath
the skin and in ligaments and tendon sheaths. They are stimulated by
rapid joint angle changes that put pressure on the corpuscle. Ruffini
endings are located in the deep skin and in the collagenous fibers of the
joint capsule. They respond to continual states of mechanical deformation
and provide information on joint position and joint position changes.
62
Other receptors in the skin, such as free dendritic endings, respond
to touch and pain and can thus act as proprioceptors. In the hands (and
perhaps feet) cutaneous afferents couple with hand motor neurons. In fact,
slight pressure to the fingers can produce relatively strong contractions of
digit muscles like the thenar muscles and the flexor digitorum superficialis
(McNulty et al., 1999).
Taken as a whole, joint capsule and internal joint receptors often
have a strong inhibitory effect on the surrounding musculature, a feature
known as arthrogenic muscle inhibition (AMI). AMI is theorized to
protect joints from overloading, especially if the joint already has damage.
For example, in knee joint injury the damage and inflammation may
activate joint receptors that serve to inhibit the quadriceps, facilitate the
triceps surae, and have either effect on the hamstrings depending on the
exact nature of injury. For example, if the anterior cruciate ligament is
damaged the hamstrings may be facilitated to help take over ACL
function. Inhibition of the quadriceps may result in weakness, motor
dyscontrol, and eventually, muscle atrophy (see Hopkins et al., 2001).
In the shoulder, a mild stimulus to parts of the glenohumeral
capsule (primarily the anterior portion and glenohumeral ligament)
produces a strong and relatively long lasting inhibition to the surrounding
musculature (Voigt et al., 1998). Addressing these reflexes is a key
component of any orthopedic rehabilitation program and is discussed in
more detail in the final chapters of this book.
Vestibular and neck proprioceptors control righting reflexes
Vestibular receptors, known also as labyrinthine receptors, detect
the movement of fluid contained in the labyrinth of the inner ear. Fluid
movement is caused by head and body movement relative to gravity, and
velocity and acceleration of head movements. They serve as major
contributors helping maintain balance and equilibrium.
Neck receptors are located in the joint ligaments of the neck and
provide information on head and neck position. They work in conjunction
with the labyrinthine receptors to help maintain balance and equilibrium.
Reflexes initiated by vestibular and neck systems are called
righting reflexes, because they help ―right‖ one‘s orientation during
falling. Righting is a result of re-orienting the head, and by activation of
the arms and/or legs in specific patterns.
According to Kandel et al. (1992) the vestibulocollic and
cervicocollic reflexes in a forward lean will cause contraction of the dorsal
neck muscles to bring the head into an upright position. Vestibulospinal
63
reflexes in a forward fall or lean will cause arm extension and flexion of
lower limbs, which is a response to brace for the fall (arms) and prevent or
limit the fall (legs). On the other hand, cervicospinal reflexes in a forward
head tilt will cause arm flexion, which is antagonistic to the vestibular
vestibulospinal reflex.
There are many other variations of these reflexes, depending on the
direction of head tilt and overall positioning of the legs and trunk. These
reflexes are among the first seen in infants and are among the most
suppressed or modified when learning new skills.
Other reflex movements arise from other receptor types located
throughout the body
Receptor reflex responses rarely work alone and are generally
coupled with other reflexes and automatic and voluntary movement
behaviors. Consider, for instance, teeth clenching during high strength
movements. Takada et al. (2000) found that teeth clenching facilitates the
reflex responses in the lower leg muscles, and reciprocal inhibition
between the soleus and pretibial muscles is abolished. The sum total of
this effect enables the lower leg to be highly stiffened, perhaps to stabilize
the body‘s posture.
The actions of many sensory
endings are to reinforce or inhibit other
reflexes. Three well-researched
reflexes, the extensor thrust reflex, the
withdrawal reflex, and the crossed
extensor reflex, provide notable
examples of this reflex integration.
In the extensor thrust reflex,
pressure on somatoreceptors,
particularly in the hands and feet, cause
a reflex contraction, or facilitation, of
extension muscles in that limb. During
a pushing movement the extensor
muscles continue to be reflexfacilitated which can strengthen the
extension movement.
Just the opposite happens with
the flexor or withdrawal reflex. This
reflex is initiated primarily by
nocioceptors in response to a pain
64
stimulus like a sharp poke or burn. These receptors signal proximal limb
flexor muscles to contract in order to withdraw from the pain stimulus.
The crossed extensor reflex combines the withdrawal reflex with
an extensor in the contralateral limb, and only functions in weight-bearing
limbs. Activation of nocioceptors or pressure receptors causes flexion of
that limb, and extension of the contralateral limb. This allows the body to
maintain balance. For example, if the foot steps onto a nail, that leg would
flex up and off the nail, the other leg would extend to compensate for the
body weight being placed on it.
Receptor and reflex summary
Sensory receptors provide invaluable information to the CNS
regarding the internal body environment and the actions of the body in the
external environment. Feedback information from multiple sensory
sources, proprioceptors and non-proprioceptors alike, provide multimodal
information to the spinal cord, and eventually to the brain. Unless this vast
array of information is filtered and encoded at both the spinal and
supraspinal levels, it cannot be used effectively in the process of producing
coordinated movement actions.
Proprioceptors may also result in a direct or indirect muscle reflex
contraction or inhibit muscle action. These reflexes are constantly
working in the background to modify, regulate, and carry out nearly every
type of movements. Inhibition
and facilitation from reflexes
may act on homonymous
muscles or distal muscles.
Though some reflexes are stable
and predictable, multimodal
inputs and supraspinal control
over reflex activity leads to the
expression of reflexes that can
differ greatly from one
circumstance to the next, or from
one person to another.
Central Nervous System Initiation and Control of Movement
The majority of brain neuronal tissue is directly devoted to
movement, and nearly every portion of the brain can have at least some
input to movement behaviors. The complexity and interconnectedness of
65
the brain make it difficult to study and even more difficult to understand.
Nevertheless, a basic understanding of neuroanatomy helps us appreciate
this complexity and take it into consideration when training individuals to
improve their motor behavior. How we can do this is illustrated using a
simple example of a flight or fight response.
The fight or flight response highlights the complexity of CNS control over
movement
Consider someone reaching down to grab his hiking shoe and
placing his hand near a scorpion. For most people a complex series of
events takes place. The visual information is routed through the thalamus
to the visual cortex of the brain. From the thalamus and visual cortex the
signal is routed to other structures like the amygdala and hippocampus.
These structures regulate emotion and memory, and in this case, strongly
influence the person‘s next move. For many people their memory and
emotion would get the best of them, and would initiate an automated panic
or startle-like response arising from the motor cortex. Conversely, an
experienced desert hiker or scorpion handler would have learned to
overcome the fear response and replaced it with a more purposeful and
calm action. Indeed, the experienced individual may reach down and
calmly grab the scorpion to remove it. This simple example illustrates that
even though there are dedicated motor control centers of the brain, the
movement plan that is constructed takes into account a vast amount of
information from all areas of the brain. Appreciation of the brain‘s
complexity reinforces the notion that training to improve movement
function sometimes needs to take into account that complexity.
Basic motor control neuroanatomy of the brain can be divided into the
cerebrum, cerebellum, and brain stem
The brain can be divided into three general regions; the cerebrum,
the cerebellum, and the brain stem. The cerebrum is made up of two
cerebral hemispheres, which can be further divided into an outer or
superficial area of grey matter called the cerebral cortex and a deep area
containing both gray and white matter. The cerebrum houses the conscious
mind and acts to organize complex movements, store learned experiences,
and receive sensory information.
Brodmann Areas and the Homunculus are Cerebral Maps. The left
and right cerebral cortexes can be mapped into the Brodmann areas.
Brodmann areas relate to functional areas ranging from speech and hearing
66
to motor function. The Broadmann areas most directly related to the
production of movement are the motor (cortex), sensory (cortex), and
association (cortex).
From the motor cortex pyramidal cell axons originate and form the
pyramidal tract, the major motor-controlling tract of neurons. These motor
neurons terminate in the spinal cord and typically make direct connections
with other motor neurons that go out to the muscles. Motor neurons from
the pyramidal and extrapyramidal tracts also make vast connections with
other neurons in the brain and spinal cord. Areas of the motor cortex that
correspond to body parts and muscles are arranged in a specific fashion.
This map of this arrangement is called the homunculus. The motor
homunculus and the corresponding sensory homunculus in the
somatosensory cortex give a strong indication of the priority the brain
gives to certain body parts. Muscles of the hands and face, though small in
mass and number, have the largest representation in the brain. The large
amount of brain tissue devoted to hands and face enable the brain to
precisely control these muscles for communication and expression of
emotion.
The motor cortex obviously plays a large role in movement, but
needs considerable inputs from other regions to produce coordinated
movements. The motor cortex integrates this incoming info from other
brain centers and then sends out a movement plan. Sensory areas,
including the auditory, visual, and somatosensory cortex receive sensory
information from the body and relay this information to the motor cortex.
The association cortex also integrates sensory areas and appears to be
involved with higher order tasks such as cognition.
Deep in the cerebrum white matter are communication linkage
areas, such as the corpus callosum. The corpus callosum links the left and
right sides, allowing communication between the sides of the brain. Also
deep in the cerebrum are pockets of gray matter called basal nuclei, or
more commonly called the basal ganglia. These structures are generally
deep to the cerebral white matter, but are also contained within it. These
information processing areas are involved with initiation, stopping, and
intensity of motor outflow, in addition to regulate learned acts of posture
and equilibrium.
The cerebellum and brain stem contribute to motor and non-motor
activities
The cerebellum sits at the base of the brain and is involved in
smooth, coordinated movements. This may be especially true for very
67
rapid movements. Cells within this structure process and compares
intended movement commands from the motor cortex and incoming PNS
sensory information, and then feeds back updated information to the motor
cortex. Research (Gao et al., 1996) has suggested that the cerebellum also
plays a role in non-motor activities, such as interpreting sensory
information, telling time, and solving puzzles.
The brain stem sits at the junction of the brain and spinal cord and
is made up of the midbrain, pons, and medulla oblongata. From these
structures come programmed, automatic movement behaviors like
locomotion and posture that are considered lower level movements. These
structures act as a passageway for all fibers between the spinal cord and
the cerebrum, processing and routing the signals like a switchboard
through various nuclei structures. This complex neural network, called the
reticular formation, receives and integrates info from all regions of the
CNS.
The spinal cord is also a CNS structure, linking the PNS to the CNS
The spinal cord is the CNS component linking to the PNS. The
outer white matter portion of the cord is mostly nerve fibers sending
signals up and down the spinal column. The interior portion of the spinal
cord is grey matter where signals are processed. The spinal cord can be
mapped like the homunculus of the cortex, with motor and sensory tracts
being located in certain areas. Direct motor functions within the spinal
cord are reflex responses. The spinal cord may tune (spinal tuning) the
descending supraspinal motor commands based on feedback to the spinal
cord from the sensory receptors.
Overview of CNS control of motor functions
Voluntary movement follows a chain of events, each link in the
chain connected to several other links with feedback and feedforward
control. It appears at this point in time
that the will to move begins
somewhere in cortical or subcortical
areas, but this is a topic of
considerable debate.
Within the association cortex,
basal ganglia, and cerebellum
movement plan information is gather
together and refined. The plan is
68
relayed to the motor cortex through the thalamus. The cortex then sends
the plan down the pyramidal and extrapyramidal tracts to the spinal motor
neurons. Feedback mechanisms work at all levels to correct errors and
refine the movement. Eventually the motor signals hit groups of lower
motor neurons and interneurons were the command information is
finalized. These motor neurons and interneurons are referred to as the final
common pathway.
Summary and Application
The workings of the peripheral nervous system, namely the sensory
endings and reflex movements, are important contributors to the overall
scheme of movement control. Reflexes produce fundamental movement
patterns, and sensory feedback provides critical information needed by the
CNS to control and regulate movements. Control of movement by the
brain is no longer believed to be contained solely within ―motor‖ areas of
the brain, but influencing and controlling structures are distributed
throughout nearly every brain region.
The practical application of this information centers on the need to
train brain integration. Factors such as experience, emotion, and purpose
drive how the brain formulates movements, and thus these and similar
psychological states must be taken into consideration in training and
practice. For example, physical training while under different cognitive or
emotional loads may train the brain in different manners, and may produce
CNS adaptations more relevant to game like situations.
Bibliography and Other Sources
Chalmers, G. (2002). Do Golgi tendon organs really inhibit
muscle activity at high force levels to save muscles from injury, and adapt
with strength training? Sports Biomechanics, 1(2). p. 239-249
Chalmers, G. (2004). Re-examination of the possible role of golgi
tendon organ and muscle spindle reflexes in proprioceptive neuromuscular
facilitation. Sports Biomechanics, 3(1), p159
Chalmers, G., & Knutzen, K. (2000). Soleus Hoffmann-reflex
modulation during walking in healthy elderly and young adults. The
Journals Of Gerontology. Series A, Biological Sciences and Medical
Sciences, 55(12), B570-B579.
Gao, J-H, Parsons, L.M., Bower, J, M., Xiong, J., Li, J., & Fox,
P.T. (1996). Cerebellum implicated in sensory acquisition and
discrimination rather than motor control. Science, 272: 545-547.
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Hoffman, M., & Koceja, D. (1995). The effects of vision and task
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70
CHAPTER 5
MOVEMENT MODELS
Chapter Outline
I. The Need for Models
II. Models of Movement
III. Reflex Models
IV. Hierarchical Models
V. The Systems Approach
VI. Summary and Application
The Need for Models
he study of motor control centers on how the brain activates
muscles to produce coordinated and task-specific movements.
Investigators have come to understand that numerous regions
of the brain are involved in producing movements and sensory feedback
from the body is used to modify movements. We saw that millions of
synapses, thousands of motor units, and hundreds of muscles are
orchestrated into producing an efficient movement, all while taking into
muscle properties like fast twitch versus slow twitch fibers and
viscoelasticity. Understanding how all these components work together
can be best understood by examining the basic frameworks for movement,
otherwise known as models.
T
Overcoming degrees of freedom is a complex challenge
One of the most difficult problems in understanding human
movement is the seemingly innumerable ways a movement can be made.
Consider, for example, the simple act of reaching for and grasping a hot
cup of tea. The brain must choose a precise pathway and speed for the
hand based on movements of the wrist, elbow, and shoulder, determine the
grip pattern and finger arrangement to hold the cup securely but without
spilling the hot liquid. In doing so, the brain must balance muscle force
output between agonist and antagonist muscles, choose which agonists,
recruit certain motor units in these muscles, and provide postural
stabilization of the trunk and shoulder. The individual must take into
71
account environmental factors, such as the temperature and slipperiness of
cup, distance of the cup, lighting, and so forth. Any number of movement
solutions can enable the final outcome of grasping the cup of tea, but the
brain must choose just one. This problem is called the degrees of freedom
problem.
In the human movement context, degrees of freedom are the
number of elements or components in the motor system that must be taken
into account to perform the task. Why or how the brain chooses one
solution over another is the object of much study. In the previous chapters
we learned that there are a few rules the brain uses to formulate and
execute movements, and these rules help reduce the degrees of freedom.
These rules, along with other factors help us construct basic models of
movement. A movement model is a general scheme or description on how
movements are formed and carried out.
Models of Movement
Models also provide a general framework of what processes and
physiological systems contribute to the formation and execution of motor
acts. We use these models for two main purposes. First, the broad goal is
to have a conceptual framework by which to understand how movements
are formulated and executed. This enables further experimentation.
Second, the models provide a framework for practical use. For example,
with a basic framework for how movements are executed we can devise
more effective programs for building muscle strength and hypertrophy,
recovering from an ankle sprain, losing weight, training surgical
techniques, recovering from nagging low back pain, improving a golf
swing, helping children learn skills from tying shoes to hitting a slap shot,
and learning to recognize a child‘s aptitude, plus many more.
Reflex, hierarchical, and systems models each give a different view on
movement production
Three basic models of movement are presented; reflex,
hierarchical, and systems. All of these models offer some level of
explanation for how movements are formed and executed, but it is only the
systems theory that we will use in an applied manner. Even with these
models we really do not understand the learning and production of
movements very well — there have been books written on the subject for
even the simplest movements without any definitive answers.
72
This framework, and use of the framework to solve movement
problems, is not complete until we get into the psychological aspects of
motor control. However, we can provide some basic and practical
guidelines at this point.
Reflex Models
Reflex models suggest that all movement stems from chaining
together of reflex actions that provide building blocks of complex
behavior. For lower animals it often works this way, for example, a
hunger stimulus like a churning stomach prompts a frog to cue in and
search for bugs. The buzzing and seeing of a fly triggers a tongue zap, and
the fly on the tongue triggers swallowing. Learning comes from classical
and operant conditioning, like the salivating of Pavlov‘s dogs. Reflex
models are based on the presence of hardwired neural circuits such as
central pattern generators (CPGs). CPGs are innate nervous system
pathways that when activated produce a coordinated movement pattern.
CPGs are innate nervous system circuits producing patterned movements
CPGs are seen in many lower animal behaviors, such as locust
flying. The figure below illustrates in very simple circuitry how the
nervous system in locusts is designed to alternately activate elevator and
depressor muscles to create wing movement. A single command neuron,
arising from the brain or other nervous system structure, is all that is
needed to provide the impulse to
set the patterning in motion. Once
Elevation
Depression
the wings get flapping they
alternately cause stretch reflexes of
the antagonist muscle, essentially
driving their own reciprocal
pattern of wing movement. Of
course, it is much more
Wing Elevation
complicated than this, and in
Command
stop
Neuron
humans the CPGs may be so
go
deeply imbedded in the nervous
go
system architecture that their
Integrating
stop
Center
existence is debated (Duysens et
Wing Depression
al., 1998).
A CPG is analogous to a
CPG Circuit
grandfather clock with a swinging
73
pendulum. The pendulum is the 'command neuron' that triggers a complex
array of gears to eventually turn the hands of the clock. The hour hand,
minute hand, and seconds hand all rotate at different speeds. No
electronics, no brain, just a hardware process that runs on its own.
Electronic timepieces also work this way, but have a battery along with a
quartz crystal to provide timing impulses to the motors that drive the
hands on an analog watch. But, can it really work this way for human
movement, or even other higher animals?
Exploiting CPGs holds promise in spinal cord injury rehabilitation
Consider the spinal cat (a cat
with its spinal cord cut just below the
brain and the animal is kept alive).
Such a cat will walk on a motorized
treadmill. The stimulus from each
paw stepping and moving on the
treadmill triggers actions of the other
legs to move in a coordinated walking
and even trotting manner. Not only
that, but practice at treadmill walking
results in longer and more
coordinated walking, suggesting that
the spinal reflex circuits learn. These
findings are supported by histochemical analyses
showing changes in spinal neuron functioning.
Accumulating evidence points to humans
having a form of CPG for locomotion, as evidenced
by body weight supported (BWS) training for
spinal cord injury sufferers. BWS is treadmill
walking with the individual partially supported by a
harness system. Presumably, this type of 'training'
forces the walking pattern and causes the spinal
cord or lower brainstem to learn (Van de Crommert
et al., 1998). Results are preliminary, but a small
number of studies (e.g., Barbeau et al., 2003) have
shown that BWS training to be more effective than
traditional physical therapy in getting stroke and
hemiparetic patients to walk, or walk better (faster,
more symmetrical). Minassian and his colleagues
(2007) did an elegant study in which they implanted
Fig adapted from V. Dietz,
Neuroscience & Biobehavioral Reviews
22(4); 495-499, 1998
74
Sketch of the study design and example of rhythmical, stepping-like movements and
associated EMG activity. The spinal cord injured individual is in supine position with the
stimulating epidural electrode above the lumbar cord. Surface electrodes are placed over both
quadriceps (Q), hamstrings (H), triceps surae (TS), and tibialis anterior (TA). EMG
recordings during tonic epidural stimulation (10 V, 25 Hz), with position sensor trace
recording induced knee movements (KM) of the paralyzed lower limb. Minassian et al., Hum
Move Sci, 26:275-295, 2007.
electrodes in the spinal cord to provide a tonic stimulation to the lumbar
region. With stimulation the patients began a stepping pattern in the legs.
The researchers also gave lumbar cord stimulation during BWS training
and found much greater leg muscle activation with the stimulation than
without.
Obviously, though, people move and organize complex movements
in ways that cannot be explained by the reflex model. Other models,
called hierarchical models, have been devised to account for brain
involvement and decision-making.
Hierarchical Models
Hierarchical models are based on top-down control, in other words,
higher brain centers send commands to lower brain centers, lower brain
centers to the spinal cord, and the spinal
cord sends signals to the muscles.
OPEN LOOP
Hierarchical systems assume that open
cont rol c enter
com m ands
loop systems dominate over closed loop
(brain)
(f eedf orwar d)
systems. In an open loop system all of the
relevant motor command information is
CLOSED LOOP
feedforward. Complete movement
cont rol c enter
com m ands
command signals originate in higher
(brain)
(f eedf orwar d)
centers and eventually make their way to
the muscles. Feedback (FB) information
fe edba ck
(f rom senso ry rece ptor s)
from the muscles and other sensory
m ovem ent eff ect ors
(m uscle s)
m ovem ent eff ect ors
(m uscle s)
75
systems comes back into the brain centers, but is largely used to prepare or
modify the next movement. The initiation of movement is purely open
loop because there has been no preceding movement to provide feedback.
In a closed loop system the FB provided by sensory receptors helps
to modify the ongoing movement. Reflex models are largely closed loop
with feedback to central integration centers essentially driving all
feedforward commands. In hierarchical models the commands from higher
brain centers (feedforward) originate independent of any feedback, though
feedback may be used to modify existing or future commands. In addition,
higher centers may oversee and regulate the expression of reflex
movements.
Schmidt's schema theory is the primary hierarchical model
Schmidt‘s schema theory posits the existence of generalized
motor programs (GMP) stored in the brain‘s memory centers. The GMP
is defined as a general representation of various actions, or a class of
actions. When the brain wants to make a movement it selects the most
relevant motor program, which contains the necessary information to
execute the movement. This GMP part of the model crosses over to motor
learning theory, but provides useful guidelines on how the motor control
systems work to reduce the degrees of freedom. The schema theory
suggests that while closed loop systems exist, motor programs are used in
the formation and execution of movement in a top down, open loop,
fashion. Closed loop feedback may help modify ongoing movements and
provide information for adapting the GMP for later movements. Similarly,
the schema theory does not discount the presence of reflexes or other
innate movement pattern like CPGs, but simply includes them as part of
the GMP.
Invariant Characteristics and Parameters. The GMP is
characterized by invariant characteristics and parameters. Invariant
characteristics, also called surface features, are those features of the class
of actions that do not change, and includes relative force, relative timing
(rhythm) of the skill components, and sequencing of the components.
Parameters are features that change within the class of actions, and include
overall force, overall duration, and the specific muscles used.
Invariant characteristics and parameters work together. Consider a
throwing movement with four parts. Part 1 is the backswing, part 2 is the
transition phase from backswing to forward impulse, part 3 the forward
impulse phase, and part 4 the follow-through. The movement is done at
three speeds (which require different absolute force levels). Each
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movement part contributes an equal
Normal speed
20%
30%
40%
10%
percentage of time (relative duration)
Fast speed 20% 30% 40%
10%
to the movement regardless of the
20%
30%
40%
Slow speed
10%
actual speed/time of the movement (the
absolute duration). The parameters
time to complete task
specify how much absolute force is
required to propel the ball normal,
slow, and fast speeds, the actual duration of muscle activity in order the
accomplish the task, and what muscles are actually involved. For instance,
in the slow movement there might be fewer muscles involved.
Experiments investigating motor program theory generally use
simple movements and straightforward experimental manipulations, like
slow speeds versus fast speeds and movements with and without accuracy
requirements. Other experiments have focused on comparing left to right
arm movement performance. These experiments, detailed below as the
speed-accuracy tradeoff, bimanual control, and the bilateral deficit,
strongly support the existence of motor programs, and further give us a
solid view that movements involve both neurophysiological and
psychological factors.
The Speed-Accuracy Tradeoff. The speed-accuracy tradeoff is one
of the most robust findings in human movement research. It is a simple
concept that with more movement speed there is less accuracy, or
conversely, one must slow down to produce
Slow Speed Movement
accurate movements. Fitts' law details this
150 ms
75 ms
20 ms
relationship:
MT = a + b(log2)(2D)
where:
W
MT = movement time, D =
distance moved, W = target width,
a,b = constants
biceps b.
15 V
15 V
triceps b.
Maximal Speed Movement
Simply stated, movement time is a
function of the distance moved and the target
size. Longer movement times at a given distance
(i.e., slower movement speeds), will occur when
there are smaller targets, because the smaller
target means more accuracy requirements. A
longer distance will mean a longer movement
time, but not necessarily a slower movement
(more distance means more time can be used to
build up force and speed, such as a wind-up).
100 ms
50 ms
20 ms
biceps b.
20 V
20 V
triceps b.
77
Thus a longer distance can often result in a faster movement, which can
further decrease accuracy.
Motor program theory explains how fast versus accurate
movements are carried out. Below are EMG traces from slow and accurate
and fast and inaccurate elbow flexion movements. The biceps b. activates
to accelerate the limb and then the triceps b. fires to stop the limb at the
target. For rapid movements the same basic movement pattern is used, but
the muscles activation becomes larger and more compressed. This
compression leaves less time for the agonist to vary its impulse, less time
for the antagonist muscle to stop at the target, and leaves no time to gather
and process feedback. Hence, the motor program needs to be specified
more completely from the outset and limits adaptability if the movement is
off target. To gain precise accuracy the movement is slowed down to allow
honing in on the target and the use of ongoing feedback corrections if
necessary.
What if there are no accuracy requirements in this task? What if,
instead of self-stopping the movement, there is a big pillow to stop the
movement? How would the EMG traces then look? In the figure below
note that the biceps b. is longer in duration and higher in amplitude in the
non-targeted movement, and because the person doesn't have to brake the
movement, the triceps burst is minimal.
Why is there even this minimal amount of triceps activity? It is
there for two reasons. The first is because it is part of the motor program
of rapid movements. It is also there because because antagonistic muscles
are functionally linked – sort of an invariant
Targeted Movement
characteristic. One muscle can scarcely be
activated without having its antagonist do
something, whether it is to stabilize the joint
or ready the limb for a reversal movement.
Antagonistic muscles commonly display
alternating or reciprocal activation patterns
that are inherent to how they work, based in
Untargeted Movement
part on reflex circuitry. Note also that the
biceps EMG is bigger in amplitude and
longer in duration. Without the need to stop
— meaning there is no need to limit the
propulsion force that might otherwise
overcome the triceps b. stopping ability —
the biceps can maximize its amplitude. But
why is the biceps longer in duration? In the
first example (when the movement needed to
78
stop), the biceps must turn itself off so that the triceps can turn itself on. If
there is only a limited amount of time to activate the accelerating muscle
and the braking muscle, and if the braking muscle can only be activated
after the accelerating muscle, then the accelerating muscle must limit it
time frame so as to allow enough time for the braking muscle to be
activated and provide force. It is similar to moving your foot off the
accelerator and moving it to the brake when driving. When moving fast
and you need to stop, you must take your foot off the accelerator well
before the stopping point so as to leave enough time/space to stop.
Remember, the muscles are functionally linked in an alternating
activation manner, and some of this linkage is through reflex activation.
Thus, without the need to activate or provide the
The speed-accuracy tradeoff
time to and activate the triceps, the biceps can be
illustrates how strategy to achieve a
activated for a longer period of time. As you can
desired outcome influences how
muscles are activated. If we take
see, many of the invariant characteristics of the
this a bit further, self-knowledge
GMP are based on neurophysiological and
(conscious or sub-conscious) of
neuromuscular properties.
our own physiological capabilities
can affect our psychological
The GMP thus gives some explanation for
strategies. An obvious example is
how the brain takes into account motor control
how pain leads individuals to adopt
characteristics to formulate a movement plan. But
movement patterns to guard against
the pain. Consider a woman with
this does not explain why speed is chosen over
leg weakness or pain that
accuracy or accuracy chosen over speed.
influences her ability to stop or
Psychological components help explain the why, or control speed. Would this influence
her plans for movement, like
strategy, of movement. Past experiences and
descending stairs? How might a
situational needs give rise to one choice or the
past history of falling further
other. For example, elders typically choose
influence her strategy? Clearly the
connection between the mind and
accuracy over speed because of a learned
body is real and plays a role in how
cautiousness. Young males tend to do the
we move.
opposite, which likely has both a cultural and
biological explanation. Strategy differences, even in a simple speed versus
accuracy situation can result in different types of muscle activation. The
psychological aspects vary the parameters in the GMP theory – a particular
strategy may alter the force or duration of the activity. If the strategy is
accuracy, then the absolute force may be decreased and absolute duration
lengthened. This strategy may also cause us to use different muscles, for
example using more wrist/hand than arm.
Bimanual Coordination. Bimanual coordination is a movement
situation involving simultaneous use of both hands. (Simultaneous use of
the legs is bilateral coordination.) According to the motor program theory,
commands must be sent to both arms at the same time: if you want to do
two different things with each arm then you send a different motor
79
program commands to each arm. This seems simple, but in practice is
difficult. The simple task of rubbing your head with one hand and patting
your stomach with the other illustrates the difficulty in doing different
tasks with each arm. So why is it so hard to do so?
To answer this question, researcher Steven Kelso and his
colleagues devised a number of experiments in which the arms or hands
were assigned to do different tasks. Specifically, each arm was assigned to
do long and short rapid movements by itself (unilateral movements), or in
combination with the other arm (bilateral movements). Sometimes both
arms did short movements or long movements (symmetrical), or
sometimes one arm moved short and the other long (asymmetrical
movements). They found that when the participants moved bilaterally in
asymmetrical movements that the arms tended to move together so that
they started and stopped at the same time. To do this, the arm moving a
long distance sped up and the arm moving a short distance slowed down.
They called this phenomenon assimilation. These results also suggested
that both arms are constrained to work as a functional unit, which has been
termed a coordinative structure. Coordinative structures are body
segments or multiple muscles whose actions are intrinsically linked
together to work as a single functional unit. The linking of these segments
or muscles generally has some sort of neural or anatomical base, but is
reinforced through practice or experience. By extension, the coordinative
structure can be unlinked through practice – extensive practice in most
cases.
Another view on bilateral control comes from experiments on
bicycle ergometer pedaling with one leg (unilateral) or both legs
(bilateral). In an elegant experiment by Ting et al. (1998) they showed that
the control mechanisms in a leg differ (and are less efficient) when
pedaling with one leg than with both legs. Thus, even if pedal rate and
force are the same, pedaling is 'uncoordinated' with one leg. This is
because each leg relies on sensory information from the other leg to set
coordination patterns. In the legs, especially, the reciprocal activation
pattern (one leg flexes, the other extends) is strongly coupled, providing
evidence that this coordinated structure may be part of some central
pattern generator system.
The generalized motor program theory fits well with coordinative
structures. As the Kelso studies have showed, coordinative structures are
tightly coupled by timing patterns. According the GMP theory, the
absolute and relative timing between limbs is stored as a component of the
task. In the cases of coordinated structures, this timing must also take into
account, or be set by, sensory info from the limbs. For example, in the
80
bicycle experiment, the 'natural' reciprocal activation timing of the legs has
a lot to do with sensory information. The GMP theoretically 'knows' this
timing pattern and uses it to help set timing patterns. Even if there is some
sort of a CPG, this does not mean the brain is uninvolved. The brain may
work with the CPG to send down the right amount of activation energy
(i.e., sets relative and absolute force) in a timing sequence consistent with
the CPG/coordinative structures.
Bilateral Transfer. Bilateral transfer is the ability to have motor
skill proficiency in one limb transfer to another limb. We‘ll take a closer
look at this phenomenon, using strength training as an example. Strength
training in only one arm will result in strength gains in that arm. It will
most likely also produce strength gains in the other arm. This is also
called cross-transfer, cross-education, or cross-exercise. Some authors
have reported up to 77% and 135% increases in strength in the untrained
limb (Hortobagyi et al., 1997).
There are two primary explanations for this phenomenon. One
explanation is based on GMP theory in that the motor program used to
produce movement in one limb is simply used in the other limb. During
training the trained limb got stronger, in part, due to changes in the motor
commands that were part of the motor program. This new and improved
motor program was then applied to the untrained limb.
The other explanation is that during training the motor program
commands for the one arm were also being sent down to the untrained arm
or to the brain structures controlling the untrained arm. This spilling over
of the motor commands from one side of the brain to another is called
central overflow, and spilling over of the commands to the untrained limb
is referred to as neuromotor overflow. If this happens, then the untrained
limb would get incidental training.
Does this happen? During unilateral exercise, electrical activity
(i.e., EMG) can often be seen in the unexercised arm. Purportedly this
overflow trains the untrained arm, but neuromotor overflow in normal
healthy people is so minimal that even if it exists it is not enough to cause
a physiological training stimulus. EMG activity seen during exercise in an
untrained limb is most often not an overflow of command signals, but
rather, is postural stabilization. Muscle action and loads on one side of the
body requires muscle action all over the body (including the opposite side)
in order to stabilize the body against unbalanced forces. Studies with
unilateral electrical muscle stimulation have reported strength gains in the
non-stimulated arm, suggesting that neurophysiological modifications in
the spinal cord contribute to cross education (Zhou, 2000).
81
In sum, the strength gains in the unexercised arm would not be
from a physiologic training stimulus in
A related issue is the concept of bilateral deficit. The
that arm: the amount of muscle activity
sum of maximal voluntary contractions (MVCs) of left
and right unilateral (UL) lifts is often greater than a
and force development, if it does occur,
bilateral lift (both arms together). This phenomenon is
is not enough to elicit a training response
most often seen in untrained persons and has both
in normal individuals. The most likely
physiological and psychological explanations. The
psychological explanation is that attention cannot be
explanation for bilateral transfer is a
directed to each limb equally, and thus maximal muscle
learned motor program modified for the
activation cannot be had during bilateral lifts. The
untrained limb in combination with some
neuromuscular explanation has been suggested by two
good papers, approaching the question from two
neural changes at the spinal level.
different perspectives (Koh et al., 1993; Vandervoort et
So what is learned and thus
al., 1984). Both papers suggest that the bilateral deficit
modified in the motor program,
is due to fewer fast twitch fibers being recruited during
bilateral activity. Because of this the bilateral deficit is
especially for strength? We can speculate
greater during faster or more powerful movements, and
that changes to how motor units are
that unilateral lifts are more prone to fatigue. Why the
activated, coordination among synergist
reduction in fast twitch activity? The authors suggested
the dispersion of concentration (i.e., splitting of
and antagonistic muscles, and controlling
attention) decreasing voluntary drive and/or some
reflex behaviors are all learned.
reflex activation. What are the implications for weight
There is good evidence for motor
lifting and power training? Before you answer this,
consider that some other authors have suggested that
programs, but motor program theory has
there is no bilateral deficit, that it is simply an
limitations and does not provide a
experimental testing-related artifact. Indeed, when we
practitioner-friendly framework. One
examine this phenomenon in lab, we will see that some
people have a bilateral deficit, but some will have a
emerging model, though, provides a
bilateral advantage/surplus.
practical framework that we can use in
real-life settings. This model, called the systems approach, does not
specifically include or exclude reflex models, coordinative structures, or
motor programs, but rather, approaches the production of skilled and
purposeful movements as outcome of many factors that interact among
each other. It is important for the practitioner to understand the
interactions of these factors, for by manipulating these factors can the most
effective training be realized.
The Systems Approach
According to Shumway-Cook and Woollacott (2001), the
fundamental concept in this theory is that movement "emerges from an
interaction between the individual, the task, and the environment in
which the task is being carried out. Thus, movement is not solely the
result of muscle-specific motor programs or stereotyped reflexes, but
results from a dynamic interplay between perceptual, cognitive, and action
systems" (p. 22). The term ―approach‖ is used because this model provides
82
more than an understanding of movement formation, but also practical
methods and tactics for implementing motor behavior training.
Action systems include those bodily systems responsible for
movement production, including neuromuscular, skeletal, and
cardiovascular. The systems approach is not fully hierarchical but has
heterarchical controllers. The Venn diagram below illustrates some of
these interactions. Consider how the social environment influences the
individual‘s movement choices or motivation, how task rules influences
movement choices, consider how boundary lines are both task and
environmental constraints.
psychological, e.g.,
cognition
memory
emotion
physiological, e.g.,
strength
metabolism
social expectations
environment
individual
Social vs physical
MOV
rules
task
regulatory, e.g,
support surface
weather/lighting
non-regulatory, e.g.,
crowd noise
distractions
boundary lines
locomotion, e.g.,
walk
run/cut
k
stabilization
tbalance
n
manipulation
grasp, hold
n catch, etc
The systems approach suggests that perception as equal, or more,
important than sensation, and thus must factor into every part of
movement individual factors that alter or affect perception. There are few
factors that do not. Sensation is what we detect in the external
environment, like temperature and light, and the internal bodily
environment, like blood pH and muscle stretch. Perception is the
interpretation of what is sensed. The same stimulus can be perceived in
widely different ways on different occasions because of different
circumstances – and can thus influence different responses. For example,
the numbing fatigue and pain in a lead runner‘s legs can be a motivator to
run harder; if feeling defeated the same fatigue and pain may cause the
runner to drag. In sum, emotional state and other psychological factors
must be considered as strong influences on motor performance.
83
Environmental factors and constraints imposed on the action must
also be considered. For example, using a high-tech tennis racquet versus
an old wood racquet might change not only player strategy, but also
particular arm coordination mechanisms. When using the wood racquet
the coordination system might set up in part to control heavy vibrations
that occur due to the properties of wood and a small sweet spot. The
coordination pattern might be to tighten the grip. With the high-tech
racquet, vibration is less a concern and thus the racquet control is different.
Recent evidence has it that the social and task environments to be the
prime influences behind the home run barrage in major league baseball
during the late 1990s. Team expectations, new stadiums, bat technology,
strength training programs, and steroids were responsible for the large
number of homeruns, but not necessarily because of technology or player
strength. Rather, these factors influenced players to play differently, that
is, to alter their swing to get more homeruns and to practice home-run
hitting swings and be less concerned about striking out.
One factor in how the action systems work is referred to as the
dynamical action theory (also called the dynamical systems theory). This
aspect of the systems theory suggests that the body has self-organizing
principles, such as coordinative structures. Another self-organizing
principle is that the body segments have certain masses and inertias and
mechanical properties like viscoelasticity, all of which influence how that
body part tends to move. For example, during walking most people walk at
a pace that is similar to the natural pendular motion of the legs. This rate
of swinging is based on the leg's length, mass, and center of gravity – all
inherent mechanical properties.
Inherent to dynamical systems is that all the systems interact and
influence one another. Change in one system leads to changes in other
systems as the interacting systems try to find a stable interaction that
optimizes or makes consistent the performance of all systems working
together, such as minimizing energy usage. For example, ventilation rate
may be tied into running pace — not simply that ventilation must increase
with the workload increase. Ventilation rate and running pace may also
need to coordinate with the bouncing movements of the internal organs
(e.g., lungs, as is demonstrated dramatically in quadrupeds, but also seen
in humans with both mechanical and neural coupling, Lee & Banzett,
1997). Further, motor and respiratory timing becomes coupled during fine
manipulation of objects, perhaps so that interthoracic pressures modify
trunk stability during object manipulation or so that afferent flow
somehow benefits object manipulation (Mateika & Gordon, 2000). The
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nature of reciprocal activation patterns of antagonistic muscles also
demonstrates a self-organizing system.
Systems work together to find a stable and consistent interaction.
Changing one system may have little impact on the whole system, but in
some cases even a small disruption in one system can de-stabilize the
functioning of the entire body. Such a destabilization may seem to be a
negative phenomenon, but not always. Destabilization causes the body to
change and adapt. For example, during fast walking a slight increase in
walking speed causes a transition to a running gait. The slight increase in
walking speed can throw off the whole system that a change to a running
gait (a much different coordination pattern) is necessary, and running
becomes the new stable state. The switch to running is a self-organizing
principle involving the organizing of metabolic, muscular, neural, and
mechanical factors, among others.
It is often necessary to purposefully cause destabilization in order
to promote new and better system functioning. Most physical training aims
at destabilization, such as the intense mechanical and fatigue stress
brought on by strength training. This stress breaks down tissues, which in
turn causes repair processes to work to create new and stronger tissues.
Destabilization does not always have such positive outcomes.
Changing one variable, even for the ‗better‘ may have a minimal impact
on overall performance. Improving strength, for example, may have no
affect on sport performance. Sometimes other systems must adapt in a
negative manner order to stabilize the system.
The systems approach provides the best framework for practical
use because it is not sufficient to simply know how the motor control
system works in order to improve motor performance. It is necessary to
know what factors – both intrinsic and extrinsic – are involved and how
these factors influence the production of skilled movement. The systems
theory gives a framework for identifying the relevant factors from task,
environment, and individual standpoints.
Summary and Application
Models have been created to explain how movements are put
together in an organized and logical fashion. Reflex models posit that
many fundamental movement patterns and behaviors, such as walking, are
simply automated hardwired reflex circuits controlled at spinal levels that
require no thinking or decision making. Hierarchical models posit that
higher brain centers control movement through a definitive command
structure. Various aspects of movements are stored in memory as motor
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programs and can be modified to different circumstances. Evidence for
both reflex control and hierarchical control are strong, but neither models
provides a workable framework that can be practically applied.
Dynamic systems theory approaches the control of movement in a
different way. This approach is based more on what factors influence the
control and production of movement, and therefore gives rise to ways to
modify movement behavior. Dynamic systems theory posits that
purposeful movement arises from an interaction of environmental factors,
task-related factors, and individual-specific factors. The brain selforganizes movements to meet the task demands in the face of constraints
imposed by the environment, task, and individual.
Shumway-Cook and Woollacott (2001) described one way to use
the systems theory to prescribe exercise and movement interventions for
rehabilitation purposes. Their approach was to start with the requirements
of the final movement, that is, to take a task-oriented approach. Their
guidelines start with a basic set of questions, but in all cases these
questions are set up to evaluate the constraints and interactions of the
individual, the environmental, and the task Consider these questions:
1. To what degree can the client perform functional tasks? What can
they do, what can they not do? What do they want to be able to do?
2. What strategies does the person use to perform tasks? Can/does
the client adopt or change strategies to changing task conditions?
3. What are the sensory, motor, and cognitive impairments that
constrain the client? Can these impairments be changed?
4. Given the set of impairments, does the client perform optimally?
Or, can some intervention help improve the clients' strategies to
accomplish tasks despite the impairment?
These questions, or this approach, can be used from highly
dysfunctioning patients to highly skilled athletes, or to ‗average‘ people
with typical ailments. Consider, for example, a somewhat overweight,
middle-aged women, lacking in motor skills (e.g., doesn't know how to
ride a bike, jumps poorly), with musculoskeletal problems like low back
pain and stiffness.
Assess what the person can do, what she cannot do, and what she
wants to do. Perhaps she has trouble playing around or carrying her young
children, but wants to. Perhaps she has trouble with climbing stairs, and
perhaps she wakes up every morning stiff and sore. Ask how she
accomplishes tasks. Does she only stand when wrestling with her children,
but really wants to get down on the floor? What are the impairments – is
she weak, lacks flexibility, does not know how to fall and roll?
Cognitively is she frightened of getting down and dirty, literally? What can
86
be done as an intervention in a typical exercise science setting, like a
health club? Answering this question goes beyond the typical exercise
prescription of aerobic exercise 3-5 times per week, strength training 2-3
times per week, and the standard warm-up, cool down, and flexibility
training. Instead, this is training for function. A summary of the systems
theory that makes mention of many of the things discussed here can be
found in Handford et al. (1997).
Bibliography and Other Sources
Barbeau, H., & Visintin, M. (2003). Optimal outcomes obtained
with body-weight support combined with treadmill training in stroke
subjects. Archives of Physical Medicine and Rehabilitation, 84, 14581465.
Duysens, J., van Wezel, B., van de Crommert, H., Faist, M., &
Kooloos, J. (1998). The role of afferent feedback in the control of
hamstrings activity during human gait. European Journal of Morphology,
36(4-5), 293-299.
Handford, C. C., Davids, K. K., Bennett, S. S., & Button, C. C.
(1997). Skill acquisition in sport: some applications of an evolving
practice ecology. Journal of Sports Sciences, 15(6), 621-640.
Lee, H-T., & Banzett, R.B. (1997). Mechanical links between
locomotion and breathing: Can you breathe with your legs? News in
Physiological Sciences, 12:273-278
Mateika, J., & Gordon, A. (2000). Adaptive and dynamic control
of respiratory and motor systems during object manipulation. Brain
Research, 864(2), 327-337.
Minassian, K. K., Persy, I. I., Rattay, F. F., Pinter, M. M., Kern, H.
H., & Dimitrijevic, M. R. (2007). Human lumbar cord circuitries can be
activated by extrinsic tonic input to generate locomotor-like activity.
Human Movement Science, 26(2), 275-295.
Shumway-Cook, A., & Woollacott, M.H. (2001). Motor Control:
Theory and Practical Applications. Lippincott Williams & Wilkins
Ting, L., Raasch, C., Brown, D., Kautz, S., & Zajac, F. (1998).
Sensorimotor state of the contralateral leg affects ipsilateral muscle
coordination of pedaling. Journal of Neurophysiology, 80(3), 1341-1351.
Hortobagyi, T. T., Lambert, N. J., & Hill, J. P. (1997). Greater
cross education following training with muscle lengthening than
shortening. Medicine & Science in Sports & Exercise, 29(1), 107-112.
Van de Crommert, H. W., Mulder, T. T., & Duysens, J. J. (1998).
Neural control of locomotion: sensory control of the central pattern
87
generator and its relation to treadmill training. Gait & Posture, 7(3), 251263.
Zhou, S. S. (2000). Chronic neural adaptations to unilateral
exercise: mechanisms of cross education. Exercise & Sport Sciences
Reviews, 28(4), 177-184.
88
UNIT 2
MOTOR
LEARNING
Motor learning is the study of how the brain plans, learns and executes
movements, and those factors that influence the planning, learning, and
executing of movements. Essential to understanding these actions is the
measurement and classification of motor skills. In this unit we will also
look at important information processing factors, especially attention,
memory, and decision making, and finally, look at practice methods.
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CHAPTER 6
MEASURING MOTOR SKILLS
Chapter Outline
I. Motor Skill Classification Systems
II. Measuring Motor Skill Performance
III. Inferring Learning
IV. Stages of Motor Skill Learning
V. Characteristics of Stages of Learning
VI. Transfer of Learning
VII. Summary and Applications
espite its name, motor learning involves more than the
learning and acquisition of motor skills. It includes any
psychological or behavioral factor that influences the planning,
production, and execution of motor skills. In order to better understand
what these factors are and their influence on motor skills, it is necessary to
classify and measure motor skill performance.
D
Motor Skill Classification Systems
Not all movements are equal. Some movements require adaptation
to a changing environment. Other movements are done with external
objects like balls. Some movements are rapid or ballistic. Some are slow,
sustained, and precise. There are, however, basic characteristics that can
help categorize or classify movements. Classifying movements helps in
teaching motor skills, monitor progression through rehabilitation, and in
prescribing exercise. Characteristics of movements that are used in
classification are generally based on (a) the precision of movement; and
(b) the stability of the environment.
Motor skills can be classified based on movement precision and
environmental stability
Classification based on movement precision generally refers to
gross motor skills versus fine motor skills. Gross movements use large
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muscle groups and generally have little precision, such as walking and
jumping. Fine motor skills use small muscles and are precise, such as
writing and sewing. Fine motor skills are almost by definition perceptual
motor skills. A continuum exists between fine and gross movements, and
many movements use both types, such as throwing.
Classification based on environmental
Researchers sometimes use a
classification scheme based on
stability refers to closed skills versus open
defining the movement beginning
skills. Closed skills are performed in an
and endpoint. Discrete movements
environment that is stable and predictable.
have a clear beginning and
endpoint such as a finger snap or
The environment, or objects in the
punch. Serial movements are a
environment wait to be acted upon by the
series of discrete movements such
individual. Examples include bowling,
as seen in playing the piano.
Continuous movements have
stationary target shooting, and golf. Closed
arbitrary beginning and endpoints
skills are self-paced, meaning that the
and are repetitive skills such as
individual chooses their own pace of action.
swimming and running. The
endpoints are determined by the
Open skills are done in a changing and
performer and the skill itself. This
unpredictable environment. The performer
classification system is mostly used
acts according to what is happening in the
in research situations, but does
help with breaking down
environment. Batting a ball, dribble a ball
movement sequences for
through defenders, and automobile driving are
instructional purposes.
open skills. Open skills are generally
externally-paced, meaning that the environment influences the timing and
initiation of the motor skill. Thus, open versus closed skills relates to what
dictates what the performer does; self-paced versus externally-paced
relates to what dictates when the performer acts.
A taxonomy of action function and environmental stability provide a
practical classification scheme
Ann Gentile, a researcher at Columbia University, devised a
classification scheme combining movement precision and environmental
stability. A simplified version is illustrated below. Movement precision
(―Action Function‖) in this model has been broken down into those
movements that require a stable body (e.g., sitting, standing), body
transport (e.g., locomotion, swimming, jumping), and object manipulation
(generally with the hands, but also includes kicking, heading balls). As we
go from tasks requiring a stable body to those that require body movement
and object manipulation, the tasks get more complicated and generally
require more attention and information processing. Gentile‘s classification
scheme includes intertrial variability, which refers to whether the
environmental context changes from one time or trial to another. This
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distinction is often used in a research context and sometimes does not
apply well in real life applications.
Action Function
Body is Stable
Body Transport / Body Position
Change
Environmental
Context
No Object
Manipulation
Manipulation
No Object
Manipulation
Manipulation
Stationary:
No intertrial
variability
Sleeping,
sitting
industrial sewing
running on a
track
reps of
clean & jerk lifts
Stationary:
With Intertrial
variability
standing at
attention
free throw
shooting,
rifle shooting
marching drills
golf, bowling
(varying pin set
ups)
Motion:
No intertrial
variability
Hide and seek
(mostly an
artificial context)
Assembly line
work, some
video games
treadmill
running
practice running
the same pass
patterns
Motion:
With Intertrial
variability
mostly an
artificial context
driving, bug
swatting,
some video
games
running
outdoors among
crowds and cars
pitching, most
team sports
Use of this and other classification schemes are useful in many
circumstances. Classifying the components of a movement aids in teaching
and rehabilitation, primarily as a guide to progress from simple to
complex. For example, orthopedic rehabilitation programs often progress
from the simplest components, like standing balance, to the more complex
components like running while manipulating an external object.
Determining the complexities of movement further aids in understanding
what psychological and physiological abilities contribute to the motor skill
performance.
Measuring Motor Skill Performance
Determining the type of motor skill and its constituent components
is important, as is measuring the quality of performance. Measuring
movement quality enables an assessment of progression of improvement
during training and rehabilitation, identifies areas of weaknesses and
strengths, and provides information for feedback. Knowing quality of
performance allows persons to be compared to standard metrics or to
others.
The measurement of motor skills necessarily includes the
measurement of motor abilities. In fact, measuring abilities may give
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insight to how an individual performs a skill. For example, after
determining a volleyball player‘s hitting skill it would be useful to
measure contributing abilities like vertical jump height and agility.
Measuring motor performance is a two step process
Evaluating a motor skill or ability requires two essential steps. The
first is determining the appropriate and valid performance measure and the
second is to test the performance measure with accuracy and reliability.
This sounds simple, but both steps are difficult and when done incorrectly
lead to assessments that are misleading and incorrect.
Establishing the appropriate measure is filled with potential
problems. Consider a collegiate cross-country running coach evaluating
high school runners. The coach wants to find the best athlete to help her
team win. What is the coach going to evaluate? She could base her
evaluation on winning percentage, but competition so varies from school
to school that the star at one school might not even make the team at
another. She could look at the athletes‘ running times, but how could she
compare an athlete running a sea level versus an athlete living in the
mountains? She could evaluate abilities, like maximal oxygen
consumption (VO2max), but how much does this really contribute to
success? Perhaps she could get hold of psychological profiles of hardiness
and confidence, but again, what associations do these have with winning?
Determining the important and relevant and valid skills and
abilities requires experience and trial and error. Rehabilitation situations
provide good examples that the important criterion measures are not
always obvious. For example, it may be more helpful in evaluating
progression of cardiopulmonary rehabilitation to know depression scores
rather than oxygen consumption, because depression scores directly relate
to the patient‘s quality of life. Likewise, an injured athlete‘s hamstring to
quadriceps strength ratio and figure-8 running speed may be less important
indicators of return to play than a subjective measure of movement
smoothness.
After the performance measure is chosen, testing must take place.
Unless the testing is accurate, reliable, and repeatable and actually tests for
the desired performance measure, it is a waste of time. It is out of the
scope of this book to discuss testing methodology, but it is important for
practitioners to know that if the testing procedures are poor then there is
no point in testing.
There are no specific rules for choosing the right performance
measure, but there are some guidelines. First, the measure must be valid,
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that is, performance on the criterion measure must reflect performance of
the motor skill. Second, the performance measure should be an important
contributor to performance. For example, strength and speed and agility
are important for soccer, but agility may be a more important contributor
to soccer success. Third, the measure must be reliable, both in terms of
administering the test and the subject‘s performance on the test.
Performance measures can be grouped into response outcome measures
and response production measures
Performance measures, also called criterion measures, can be
loosely grouped into two categories. The first, response outcome
measures, measure the result of a particular skill. These measures reveal
what happened, not how it happened. Response production measures
indicate how a response was produced. Note that these categories are not
mutually exclusive. Sometimes a response production measures can be
used for response outcome measures and vice-versa.
Response outcome measures include reaction time and error measures
Specific response outcome measures generally include measures of
speed (e.g., velocity), time (e.g., 0.25 seconds slow), accuracy, and
direction. Among the most popular response outcome measures used in
research but often overlooked in sport settings, is reaction time (RT).
Reaction time is measure as the time from a stimulus to the onset of a
response. It does not include movement and is thus used to measure the
information processing time involved in a task. RT can be fractionated
into premotor time (stimulus to onset of muscle electrical activity) and
motor time (onset of muscle electrical activity to response initiation).
Motor time can also be termed electromechanical delay (EMD). Longer
RTs mean more information processing is required. Information
processing is discussed in the next chapter.
Reaction time itself is one component of total response time.
Total response time (RpT) is the time from a stimulus to the completion of
the response. It thus includes RT and movement time (MvT). Movement
time is defined as the time from the onset of movement to the movement
completion. Individuals with fast movements are often said to have fast
reactions, but this is not necessarily the case. Reaction time and movement
time are separate processes that often do not mirror one another. Put
differently, something that slows down movement speed may have no
influence on reaction time, or vice-versa. In some instances, though, the
94
same factor can slow down or speed up both reaction time and movement
time.
em g tra ce
Wa rning
Signal
For eper iod
St art or
Go Signal
Mo vem ent
Initiat ion
pre mot or time
m otor t im e
T erm ination
of Response
Mo vem ent T im e
Reac tion T ime
Response T im e
The illustration above also shows a foreperiod that that is a time
period that comes after a warning signal and before the stimulus. A
warning is not the stimulus itself, but may enable the individual to
anticipate that a stimulus is coming and even what that stimulus may be.
Reaction Time Paradigms. The very fastest motor reaction times
are about 150 – 250 ms and occur in situations in which there is only
stimulus and one response. This simple RT paradigm requires the least
amount of information processing and thus has the fastest times. More
complex RT situations include discrimination RT and choice RT.
Discrimination RT situations are characterized by having many
stimuli, but only one of the stimuli is meaningful and there is only one
response to the stimulus. These situations require more information
processing than simple RT because the individual must determine whether
the stimulus presented is the right one. Choice RT situation have two or
more stimuli, and each stimuli has its own response. Choice RT is usually
the most difficult and results in the slowest RTs, as individuals must not
only the nature of the stimuli, but what response goes with the stimulus.
In the laboratory, simple and complex RT paradigms are easily set
up and manipulated with lights, buzzers, and key presses. Outside the
laboratory simple RT situations are not easy to find, and complex RT
situations can be overwhelming. Automobile driving provides excellent
examples of complexity, such as when a ball rolls out into the road from
between parked cars on the driver‘s right. The ball seems to be a simple
stimulus, but the driver‘s responses are dependent on other stimuli as well,
such as oncoming traffic. The basic response choices are swerve left,
swerve right, brake, or do nothing. Generally there would be two common
95
responses; brake or swerve left. Both may result in loss of control,
confusion on the road, and an accident. Swerving right is a poor choice
because of the parked cars or the chance of a child following the ball.
Doing nothing is often the best choice because hitting the ball is nothing
compared to a vehicle accident. But this response rarely happens, because
where there is a ball there is apt to be a child chasing after it. The best
response, therefore, may be to brake, or to do a visual search for children,
oncoming traffic, or tailgating traffic. If the driver has already done a
visual search and knows the traffic and child situation, then the response
choice is easy and can be made rapidly. In conclusion, what appears to be
a simple visual stimulus with one logical response is really a complex
situation-dependent reaction time paradigm that relies greatly on the
driver‘s skill and specific environmental circumstances.
Measures of Error. Error measurements are used to determine
accuracy of responses, which can be spatial (in space) or temporal (in
time). Several different types of error measures, used with both temporal
and spatial accuracy, can be used to gain an understanding of what caused
the error and how to instruct performers to better their performance. Each
error score provides one bit of information and thus must be interpreted
carefully to gather important information. Generally, an error score is
provided after several trails.
Constant error (CE) is simply the average error over a given
number of trials. The score is based on both the magnitude and direction of
error and thus provides not only a measure of how much error, but a bias
or tendency in the performance. Absolute error (AE) is the average over a
given number of trials of the error absolute values. Thus, no plus or minus
or direction of the scores is provided, just the error magnitude. Variable
error (VE) is the standard deviation of the group of error scores. It is a
measure of the consistency of the responses and not the amount of error.
Response production measures include biomechanical and EMG measures
Response production measures are those that pertain to how, or
even why, a movement was done. Kinematic measurements of
displacement, velocity, and acceleration, and kinetic measures of force and
torque describe characteristics of movement without necessarily revealing
the outcome of the movement. These biomechanical measures can be
made with sophisticated goniometric and videographic technology, but are
often done in a more subjective or qualitative manner by observation. For
instance, a coach may identify a poor ball toss as a reason why a tennis
serve hit the net.
96
Electromyography provides information on muscle timing, strength
of contraction, and muscle function that underlie motor skill performance.
It can be used to examine muscle dysfunction and has other clinical uses in
rehabilitation such as biofeedback.
Inferring Learning
If we have tested an individual before and after a period of
practice, how do we know that learning has occurred? Does improvement
from pretest to post test indicate that the person has learned? It may seem
obvious that improvement means learning has taken place, but in fact, we
do not directly observe learning; we only observe behavior and thus must
determine if the motor behavior reflects learning.
Learning is a relatively permanent change in capability
Learning is defined as a relatively permanent change in one's
capability to perform a skill as a result of practice or experience. This
definition implies that the potential, or capability, is improved, not
necessarily the actual performance. There are a number of things that may
inhibit performance despite learning taking place. Motivation, anxiety, and
fatigue are just a few of the things that can lower performance even though
learning is taking place. The definition of learning also states that learning
is a result of practice, which means that improved performance due to
growth or maturation or luck does not reflect learning.
Theoretically, we cannot directly assess learning as it is an internal
phenomenon that is not directly observable. Instead, performance as the
observable behavior is measured and learning is inferred from observation
of performance. Usually performance can give a good indication of what is
internal, but not always. In order to infer learning, several performance
characteristics are assessed. The first is persistent improvement over time.
The second is better consistency. Performance should become less variable
from trial to trial and day to day.
Performance plateaus make inferring learning difficult
Improvement in performance over time rarely follows a steady
path. Sometimes improvement rises rapidly, sometimes it levels out. In the
illustrations below, each graph has areas of little or no improvement in
performance. These areas are called plateaus. Even though performance
improvement may have stopped, learning may still be continuing.
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Plateaus may be caused by several factors. The first is that the
individual may simply lack motivation or attentional focus, or may be
fatigued. These factors are called performance variables in that they may
affect performance and not necessarily learning. Learning variables can
affect both learning and performance. Next, the plateau may reflect a poor
performance measure. It could be the performance measure is so easy that
the person maximizes the score quickly, leaving little room for
improvement. This is call the ceiling effect. Likewise, if the measure is so
difficult that improvement is difficult to come by, this is called the floor
effect. Among the most common reasons for plateaus can also be the most
frustrating. As peformance improves it is often necessary to progress
through a hierarchy of new skills or learn new abilities, requiring the
learner to change what they are doing. As learners are going through new
tactics and strategies, performance may suffer. For example, an
accomplished volleyball player may begin learning a topspin serve to
replace her well-learned and successful straight serve. Performance of the
serve stabilizes – she has reached a ceiling because there is little room for
improvement of this base level skills. To get better the player must learn a
topspin serve. In learning this new skill she becomes somewhat of a
novice performer and her serve performance suffers. Nevertheless, she
may be learning a great deal even if her serve performance does not reflect
it. Last, a learner may hit a plateau when teaching is not appropriate or
specific to meet the needs of the learner. Overall, plateaus are more of an
artifact rather than a real phenomenon of learning.
Stages of Motor Skill Learning
The previous section on plateaus implies that learning occurs in
stages over time, and it does. At various stages of learning there are
different things, whether cognitive or physical, that become important in
the learning process. Sometimes previously learned skills need to be
abandoned. Sometimes new abilities must be gained so that new skills can
be learned. At each stage the teaching and learning strategies may also
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need to change. Fitts and Posner’s 3-stage model and Gentile’s 2-stage
model give us an idea of what changes learners go through as they
progress from one stage to another. These models help to identify where
the learner is at, and what to expect for further improvement. Both models
assume that learning starts cognitively and end with automatic movements.
Learning stage models progress from cognitive to associative to
autonomic stages
Stage 1 of the Fitts and Posner model is the verbal-cognitive stage,
or simply the cognitive stage, implying that most of the learning is not
reflected in motor performance changes. During this stage the learning
includes understanding rules, getting a feel for the concepts for movement,
learning tactics, and even learning how to learn. Gentile termed this stage
the idea of movement stage as the learner begins to grasp the fundamental
ideas of movement and determines what must be done to move. To do so,
the learner determines proper stimuli and establishes a movement pattern.
In determining the proper stimuli the learner identifies stimuli that are
relevant to the movement, like ball speed, and non-relevant stimuli or
distractions that must be ignored. There is certainly improvement and
learning in motor performance, but not necessarily to the extent of
improvement in task knowledge. Performance in Stage 1 is characterized
by many errors, gross errors, and high variability. Learners are not aware
of how to correct the errors. The learner is also beginning to establishment
movement patterns, which may include footwork and limb coordination.
Stage 2 is the associative stage. Fundamentals are learned and
fewer and smaller errors are made. Concentration is on skill refinement as
the learner begins to detect and correct errors. Thus learners can alter their
own practice and reduce performance variability.
Stage 3 is the autonomous stage. It only comes with much practice,
after which the skill becomes automatic. The learner is able to perform the
skill without 'thinking'. Errors can be detected and corrected, often during
the task itself. Gentile noted that during the last stage that the learner goes
through phases of fixation and diversification. The learner fixates on
specific movements developed in earlier stages, refining them to make
them more effective, more consistent, and automatic. For ongoing learning
to take place, movements must be then adapted to different situations, or
adjustments made to fit specific needs. This means that a larger number of
motor patterns must be developed. Gentile termed this adaptation to be
diversification, effectively expanding the learner‘s movement repertoire
99
These three stages are sometimes labeled a beginner, intermediate,
or expert stages, but these labels are not correct. There is a great range of
skill levels that can fall within each stage. Automaticity, for instance, does
not make one an expert. Bicycle riding is automatic for many people, but
few of these people would be considered expert cyclists. Conversely, an
expert gymnast may struggle learning a new routine, temporarily rendering
them as beginner or intermediate performers.
Characteristics of Stages of Learning
Identifying the stage a learner is at is not an easy task. Simply
inferring automaticity and levels of error correction are insufficient, in part
because the learner may be at different stages in different component of a
complex skill. There are other characteristics to look for that help identify
a learner‘s progression and overall level of skill proficiency. In addition to
error detection and correction, these characteristics are (1) knowledge
structure, (2) how the goal of the skill was achieved, (3) changes in
coordination, and (4) improved movement efficiency and muscle
activation changes.
Learning creates a different knowledge structure and better information
processing
As learners progress through the learning stages, they process
information faster and more accurately. They know more information and
are able to use that information in different ways. For example, experts use
concepts, not just independent pieces of information. They also relate
information together better, a process called chunking. For instance, late
in a soccer game an offensive player may put together a series of ‗clues‘
about the game circumstances (e.g., score, fatigued defenders, defender
tendencies developed over the course of the game) to decide and
implement a particular tactical move.
A different knowledge structure is accompanied by different visual
search patterns. Early learners typically look at only the most direct and
immediately important cues, such as watching the ball. Individuals later
begin to learn to look for different stimuli or clues to help them anticipate
and perform better. For example, experts watch the body language of
opposing players in sports like tennis in order to anticipate where the
player intends to hit the ball or move. At the highest level of success, it is
most often these skills that distinguish the best players.
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Better skilled persons change how the goal of a skill is achieved
As learners improve they change how they accomplish goals. For
instance, beginning soccer players may emphasize kicking power when
goal shooting, whereas a more skilled player relies more on an accurate
and deft touch. Beginners may drive the ball directly at the goalie, experts
attempt to fool the goalie. How the learner achieves the goal of the skill is
very task dependent and is a combination of the learner‘s knowledge base
and an already accumulated skill set.
Experts have better coordination and movement efficiency
That experts have better coordination seems almost a definition of
expert performance. This coordination looks different depending on the
task, but there are some common characteristics of highly coordinated
movements, some of which we examined in the motor unit behavior
section. Overall, experts tend to use less muscle activation for a given task,
which produces smoother and more energy efficient movements. On the
other hand, experts often have the capability to call upon more
neuromuscular resources to maximize performance.
Whole body coordination differences are often easy to spot.
Novices tend to look stiff and jerky, which can be a result of them linking
together limb segments to act as a single unit. This helps simplify the
action for the novice, in effect reducing the degrees of freedom. Experts
smoothly transition forces from body to limb and have fewer extraneous
movements.
Learned Coordination and Physiological Consequences. The
characteristics that describe one‘s progression through learning stages are
not limited to learning motor skills. They are important even for
progression in activities that many consider to be largely based on genetic
physiological capacities. Consider the importance of muscle coordination
and movement efficiency as they related to a study by Lay et al. (2002),
who had fit subjects practice a rowing ergometer exercise over just 10
practice days. The subjects practiced at an intensity level too low to elicit
physiological adaptations. After the 10 days of practice the subjects were
able to exercise at a submaximal work level using less energy (e.g., VO2
consumption) and less EMG activation than before practice. Other results
found more tightly coordinated muscle activation patterns and movement
patterns as revealed by biomechanical analysis. These authors suggested
that coordinative mechanisms were organized to minimize metabolic cost
(or maximize efficiency). Similar results have been suggested for cycling,
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where the differences between international and national level cyclists (all
outstanding) are not in VO2, not in strength, but in the coordinated
workload distribution across muscles that enables force sharing.
Transfer of Learning
One of the key features in learning is that what is learned in one
situation can often be applied in another situation. This phenomenon,
called transfer of learning, enables individuals to learn of new skills and
diversify their movement repertoire, that is, if the transfer is positive.
Positive transfer facilitates the learning of the secondary motor skill,
whereas negative transfer impedes learning of the secondary skill.
Transfer occurs more among similar tasks
Transfer occurs more when there is similarity, or identical
elements, among the skill components or context under which the skills
are performed. For example, an overhand throw has elements similar to an
overhand serve in volleyball and tennis. More transfer also occurs when
there is similarity of information processing requirements or previous
experiences. This type of transfer is often seen in applying team tactics
and strategies from one sport to another sport, such as the basis for a zone
defense used in many team sports. Another common example is that
experienced athletes know the type of moves that throws a defender off
balance, which can work in multiple sport settings.
There is more transfer when there is both identical elements and
similarity in information processing, but this transfer is not always
welcome. Transferring learning from one skill or context to another
usually leads to positive secondary performance, at least initially. In some
cases, however, this transfer is negative and impedes the learning of the
secondary skill because the individual finds it difficult to break away from
the initial learning. Hockey and baseball players, for example, may have
negative transfer when playing golf. At first, these players may have
positive transfer of basic hand-eye coordination and body mechanics, but
after time the automatic hockey and baseball swings fail to enable
progression in the golf swing, which requires a more calculated and
patterned action. The swing habits of hockey and baseball have thus
become a difficult to break bad habit for golf. Learning in these cases may
become difficult and confusing for the learner, though negative transfer
should always be thought of a temporary. Negative transfer is most likely a
result of cognitive factors, not identical elements.
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Transfer has important benefits
Without transfer it would be impossible to progress through the
stages of motor skill learning. Simple tasks learned early are built up into
complex skills. In addition, transfer enables those skills learned in practice
settings to be applied in real situations. Because of transfer, we can gain a
better understanding of the theoretical process of learning and how to go
about sequencing the learning of a complex skill. For example
fundamentals are learned before complex movement patterns, which is
especially important for dangerous skills such as diving and some
gymnastics routines.
Summary and Applications
Motor skill can be classified according to characteristics of the
skills, including locomotion and manipulation, and the open versus closed
environment the skill is performed. Classification schemes enable a better
understanding of how motor skills are performed and are useful in learning
and rehabilitation settings. Measuring the quality of performance is a
challenge because of measurement difficulties, and validity and reliability
issues. Nevertheless, is it important to measure performance as a way to
gauge progression of improvement and to infer if learning is taking place.
Two general types of performance measures – outcome and production –
offer different way of assessing performance level and interpreting
learning. Reaction time, as a measure of information processing, is an
underutilized performance measure in sport and exercise settings.
Learning progresses through stages, generally new learning is
highly cognitive as learners get the feel for movements. Well-learned
movements are automatic and are performed with more consistency and
fewer errors. Among the other characteristics that are learned over time
include better coordination and better information processing. In many
instances higher skilled performers are best separated from other
performers by knowledge base and better and faster information
processing. This highlights the important premise that even with great
physiological abilities like strength, and even with outstanding technical
skills like basketball dribbling, such skills and abilities are useless unless
they are done at the right time and under the constraints imposed by the
task circumstances. For example, spending countless hours in the weight
room may produce incredibly strong muscles as measured by maximal
weight lifted, but unless that strength can be used at the right time under
the right circumstances, the strength has gone to waste.
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Bibliography and Other Sources
Abernethy, B. B. (1999). The 1997 Coleman Roberts Griffith
address movement expertise: a juncture between psychology theory and
practice. Journal of Applied Sport Psychology, 11(1), 126-141.
Baker, J. J., Cote, J. J., & Abernethy, B. B. (2003). Sport-specific
practice and the development of expert decision-making in team ball
sports. Journal of Applied Sport Psychology, 15(1), 12-25.
Baker, J. J., Horton, S. S., Robertson-Wilson, J. J., & Wall, M. M.
(2003). Nurturing sport expertise: factors influencing the development of
elite athlete. Journal of Sports Science & Medicine, 2(1), 1-9.
Coyle, E. F. (1995). Integration of the physiological factors
determining endurance performance ability. Exercise & Sport Sciences
Reviews, 2325-63.
Lay, B. S., Sparrow, W. A., Hughes, K. M., & O'Dwyer, N. J.
(2002). Practice effects on coordination and control, metabolic energy
expenditure, and muscle activation. Human Movement Science, 21(5/6),
807-830.
McPherson, S. L. (1994). The development of sport expertise:
mapping the tactical domain. Quest (00336297), 46(2), 223-240;247-262.
McPherson, S. L., & Vickers, J. N. (2004). Cognitive control in
motor expertise. International Journal of Sport & Exercise Psychology,
2(3), 274-300.
Wright, M., Bishop, D., Jackson, R., & Abernethy, B. (2010).
Functional MRI reveals expert-novice differences during sport-related
anticipation. Neuroreport, 21(2), 94-98.
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CHAPTER 7
INFORMATION PROCESSING
Chapter Outline
I. Multiple Resource Theory
II. Memory
III. Attention
IV. Intention, Effort, and Attention
V. Summary and Applications
he job of our central nervous system is to process information.
In brief, information is identified, interpreted, and acted upon.
Our brain reasons, acts, stores information, retrieves information, monitors
and runs the physiological processes of our body, produces emotional and
rational behaviors, communicates, and makes decisions. But it cannot
necessarily do all this at one time. Our brain has limited capacities that, in
turn, limit our performance. In this section we will look at multiple
resource theory as a model of our brain‘s information processing, and then
two information processing resources. These resources – memory and
attention – factor prominently in the application of motor learning
principles.
T
Multiple Resource Theory
The processing the brain does is widespread and varied. Multiple
resource theory posits that we have a variety of processing resources.
Though our brain has areas to process specific types of information, such
as verbal output, auditory, olfactory, visual sensory processing, and
emotional reasoning, these do not necessarily correspond to resources as
identified by multiple resource theory. Nevertheless, the theory adequately
describes that our brain has the capability to process different types and
amounts of information, though there is redundancy in the system. All of
these resources have limited, but flexible capacities. Sometimes the
resource capacities can be expanded, and are often times shrunk. Factors
such as arousal, fatigue, motivation, and health can alter the capacity.
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If two or more tasks require the same resource then conflicts may
develop and slow down or impair processing. A single large processing
requirement may also tax the resource capacity. If two or more different
tasks are done then different resources may be called upon, thus capacity
may not be limited. However, capacities can be taxed easily under
multiple tasks. Driving in heavy traffic and bad weather provides a good
example of taxing resources. Even as the driver slows down, there is a
good chance the radio will be turned off and passengers told to quiet
down. The need to concentrate on the environmental conditions is so
consuming that all resources are diverted away from listening to music and
carrying on conversations. Furthermore, there is a good chance that stress
and anxiety will consume resources and divert attention. Current evidence
on the dangers of texting and driving provide a sobering reality to the
resource limitations of our brains.
Memory
Memory is a cognitive processing function that people tend to
associate with facts and figures, and not motor skills. Indeed, the common
phrase, ―Once you‘ve learned to ride a bike, you‘ll never forget,‖ implies
that we do not need to try and remember motor skills. Memory, however,
plays a critical role in the learning of skills and in high level performance.
The simple ability to repeat large numbers of motor skills over and over
again indicates that we have a large capacity for motor memory. During
activities we rely on non-motor memory to improve performance. A soccer
player, for instance, may scan the defense and instantaneously recall a
previous pattern of play, giving the player information to anticipate a
defensive strategy. Motor memory is sometimes mistakenly called muscle
memory, a term that holds no real definition in the scientific literature.
Memory can be roughly broken down into working memory and
long term memory. Working, or short term, memory is the temporary use
and storage system for information. It is the active system for information
processing, especially for the immediate situational needs, such as decision
making, problems solving, movement production and evaluation, and
storage and retrieval of long term memory information. Information lasts
only about 30 seconds in working memory. Capacity of working memory
is about 7 (+ or – 2) words or digits. In movement, this translates to about
7 sequences in a movement (e.g., discrete gymnastic movements). Highly
skilled people have larger working memory and long term memory
capacities that are skill specific.
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Long term memory is the ‗permanent‘ repository of information.
Within long term memory is stored procedural, declarative, semantic, and
episodic information. Procedural information refers to how to do
something whereas declarative information is what to do. Semantic
information is a general knowledge of the world – facts and concepts –
gained through experience and episodic information is personally
experienced events and the times they occurred.
Improving and facilitating memory storage requires purposeful strategies
There are three basic factors that must be taken into consideration
regarding memory retention. First, the characteristics of the movement
itself influence what is remembered. Second, remembering strategies
influence retention, and third, the characteristics of practice influence what
is remembered for and test situations.
Movement Characteristics. Several factors about movements are
related to the ability to remember them. Continuous skills are more
resistant to forgetting than discrete skills, probably because of their
repeated nature. Location and distance features are important features that
are remembered – location seems to be better or easier remembered. Thus,
pointing out important positions of the body is a good instructional
method. For example, remembering an initial stance position gives
information on the movement to follow, and remembering a final position
enables the learner to work through the movement that lead to the end
position. First and last positions of a movement are naturally better
remembered, as are proper or natural movement sequences. Because of
this, though, middle portions of movement sequences tend not to be
remembered as well, though they may be just as important and thus may
require additional memory effort. For example the middle stage of a golf
swing with the club head back up over the head and the body cocked and
ready to swing the club forward, is a crucial position for an effective golf
swing. Though it is in the middle of the movement, if this critical point is
identified to the learner as important and made meaningful, then it is much
better remembered.
Remembering Strategies. There are five basic memory strategies
that can be used depending on the appropriate circumstances: (1) rote
repetition, (2) meaningfulness, (3) preselection, (4) intention to remember,
and (5) subjective organization.
Rote repetition is repeating the movement again and again and
again. This is a fundamental tenet of all of practice, but it does not
necessarily mean that the exact same movement is repeated. Even the
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seemingly most similar movements, like forehand drives hit off a ball
machine, are coordinated in different ways as the nervous system
continually refines the movement. According to Bernstein (1967),
The process of practice towards the achievement of new motor
habits essentially consists in the gradual success of a search for
optimal motor solutions to the appropriate problems. Because of
this, practice, when properly undertaken, does not consist in
repeating the means of solution of a motor problem time after time,
but in process of solving this problem again and again by
techniques which we changed and perfected from repetition to
repetition. It is already apparent here that, in many cases, "practice
is a particular type of repetition without repetition" and that motor
training, if this position is ignored, is merely mechanical repetition
by rote, a method which has been discredited in pedagogy for some
time. (p. 134)
With this kind of repetition, what is stored in memory is the refined
movement along with the ability to diversify the movement pattern.
Meaningful movements are better learned and remembered.
Attaching meaning can be more complex than simply stating that it
meaningful; the learner needs to understand the meaning. It can be useful
in attaching meaning to have the learner visualize the movement or attach
a verbal label to a specific aspect of movement. These techniques may also
serve as mnemonic devices.
Preselecting the movement means have the learner selects what
movements they wish to work on. In doing so, it is likely that the learner
pays more attention and devises his or her own methods of remembering.
Often times preselection is coupled with adding meaningfulness.
The intention to remember seems an easy concept, but is often not
done. Movements are best remembered when willful effort is given to try
and remember the activities during practice.
Subjective organization is a process in which movements or large
skill sets are organized by the learner. Movements then tend to be
organized not only in a way that is meaningful, but in a way that fits the
way the learner learns. This does not mean that the learner is the only one
responsible for practice and remembering, as this strategy may contribute
to learning the wrong things. The instructor must help guide the learner‘s
organization.
Practice-Test Characteristics. A beginning driver may learn to use
the clutch and brake and stick shift with great skill – remembering shift
patterns and so forth – during simple driving on a protected track that
poses no obstacles or dangers. These same skills, however, may not be
displayed on congested city streets, in fact, the driver may freeze, grind
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gears, or not know where the gears are located. This is an example of the
practice circumstances being different from the ―test‖ circumstances and
memory being specific to the characteristics of the learning environment.
The more that practice is like the game the better the memorization will be
in the game or on the test. Part of this is due to the storage of specific
sensory information.
Attention
It is apparent from multiple resource theory that for optimal
information processing to take place the amount of information coming
into the system cannot be overwhelming. This can happen in two ways;
the first is to limit what actually comes into the CNS and the second is for
the CNS to filter out or ignore information before it is processed further.
Both happen, but for our purposes it is most useful to examine the process
of limiting information before it reaches our CNS. We do this by altering
our attention.
Attention is the mental process of selectively concentrating on one
thing, that is, a specific allocation of processing resources. Attention can
be placed on the external environment, on the internal bodily environment,
or on mental processes themselves. For example, mental math and
daydreaming both place attention on mental processes. Placing attention
on specific things is called selective attention, and is one of the keys to
avoid overburdening information processing resources. Selective attention
implies that attention is placed on the most important, or most meaningful,
things relevant to completing a task while ignoring other stimuli. Focus of
attention is sometimes used interchangeably with selective attention, but
means something different. Focus of attention refers to the quality of our
concentration on a stimuli or ongoing situation. With a poor focus of
attention our minds may drift to irrelevant information, thereby allocating
information processing resources away from what is necessary.
It is necessary, particularly in the sporting environment, to
attention switch from one stimulus or information processing resource to
another. A long distance runner, for example, may place attention on a
nearby competitor, shift to tactical decisions, shift again to monitor his
internal physiological state, and then shift back to tactics. A quick and
transient switch in attention switching is called a momentary intention.
For example, while playing tennis the player can attend to the ball, and
then quickly switch attention to monitor the actions of the opposing player.
In sum, the ability to focus attention, switch attention, and select
the most meaningful cues and information to concentrate on, is necessary
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to avoid a cognitive meltdown. How we identify the most meaningful and
important information, how we increase our focus, and how we learn to
switch attention is learned through practice and is very much situation and
context specific.
Attention demands vary with motor skill performance
The attention requirements of motor skills are quite varied.
Furthermore, for a specific motor skill the attention requirements may
change depending on the situation or circumstances surrounding the
execution of the skill, and may differ from person to person. One of the
most noticeable aspects of attention is that the demands of attention (i.e.,
those things that require our attention) change over practice. In particular,
some tasks demand less attention as skill level improves. As tasks become
automatic the need to place attention on actual movement execution is
reduced. This automaticity, though, does not mean that our minds are free
to wander. What it means is that resources are freed up to be used
elsewhere. Yogi Berra, Hall of Fame catcher for the NY Yankees, once
remarked that ―you can‘t think and hit at the same time.‖ More
specifically, Yogi was succinctly stating that you can‘t think about the
swing while placing attention on the ball at the same time.
The concept of automaticity illustrates that attention requirements
change over learning stages. With improving skills the learner is freed to
place attention on other cues, has an increased capability to place attention
on new cues, and learns the important information to process and the
irrelevant information to ignore. Conversely, these new attention skills
improve motor skill performance.
Attention skills are learned both explicitly and implicitly
Attention skills are generally not explicitly taught, save for the
exception to ―keep your eye on the ball,‖ or ―watch the other player‘s
move.‖ Such limited instruction in attention is not necessarily an oversight
because attention skills are learned both explicitly and implicitly. Specific
practice at attention skills, like watching the ball, are explicit, whereas
incidental learning that comes without an awareness of what is being
learned is called implicit. High level athletes will often talk about picking
up movement cues from opposing players, like shoulder rotation during a
volleyball serve, but can rarely say when or how they learned it. Rather,
they just ―picked it up along the way.‖
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Attention switching and selective attention are often learned
through a trial and error approach. Over time and trials, learners figure out
which cues are important and should be attended to, and which cues are
irrelevant and should be ignored, particularly depending on the situation.
Intentional practice should be used when appropriate to facilitate and
speed up learning.
Attention capacity and instruction
Though the type of motor skills influences attention requirements,
and often times attention skills are learned implicitly, there are a number
of instruction concepts that can help the learner understand and learn the
attention demands of a particular skill. These instruction hints emphasize
movement initiation, breaking down the movement, and the focus on
external cues.
The initiation of the movement generally requires more attention
than the rest of the movement, and without a good start the rest of the
movement may suffer. Particularly for new learners, not only does the
movement initiation demand attention, but by placing attention on the
initiation of movement the whole movement may be better served.
Not all components of the movement require the same amount of
attention. Movements can be broken down and separated into parts that
require a lot of attention or are more meaningful. In addition to the start of
a movement, sometimes there are key phases in a movement that are
attention-demanding. For example, the leaping off the ―jumping leg‖
during a lay-up in basketball. This important transition from dribble to
shoot requires attention initially, and should be developed to a point of
automaticity.
Focusing on external cues rather than internal cues appears to
facilitate performance and learning. For example, instead of focusing on
the hands or ―feel‖ in a golf swing, the focus should be on the club head or
a movement outcome. In the past decade an abundance of research reports,
many from Gabriele Wulf and her colleagues, have shown that motor
skills, are learned and performed better when attention is placed
externally. It is believed that focusing on a specific movement outcome
simplifies the brain‘s movement planning, and essentially enables the
brain to organize the most effective solution to the movement problem.
Focusing externally, also called a dissociative focus, has been
shown to reduce ratings of perceived exertion in runners, but some reports
indicate that accomplished aerobic athletes often maintain an internal, or
associative, focus on their own physiological processes, like heart rate or
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fatigue. This self-monitoring enables these athletes to regulate their efforts
appropriate to the environmental challenges and their own race strategies.
At high levels of effort it becomes extremely difficult to ignore the
overwhelming physiological signals of fatigue, pain, and stress, but even
then high level athletes are able to attention switch to external factors such
as competitors and environmental circumstances.
Knowing What is Meaningful. It is important to place attention on
relevant and meaningful cues and information that will enable better
performance. This is not always easy to do, even when proper focus and
selective attention has been learned. There are a number of things that
draw our attention, even if it is not relevant to the movement. These
factors are unexpected stimuli, visual information, and meaningful but
irrelevant information.
Unexpected stimuli almost universally our attention. Loud noises,
out of place movements, surprise bodily feelings like ―twinges‖, and other
inconsistencies in what we expect draw our attention. Sometimes it is
appropriate to attend to these stimuli, like an emergency siren, but often
times it is not. Indeed, opposing players often make unexpected
movements or sounds in an attempt to distract another player.
Visual information tends to draw more attention than other sensory
cues. But be aware that any strong stimuli, like loud noises, acrid smells,
and pain draw much attention, particularly if unexpected.
The most meaningful information or stimuli draws attention, but
paradoxically, this information is not always understood by the learner to
be relevant to the task. Attaching meaning to information is an essential
part of the learning process, both implicit and explicit. Keep in mind that
what is meaningful information can change rapidly during a task, and
underlies effective attention switching.
So how does a learner ascribe meaning to information so that they
place attention and allocate resources most effectively? Learners can be
instructed on what to place attention and why, but until a learner places his
or her own meaning to stimuli or information, it will not fully capture
attention. Learners must be challenged to explore and change where they
place attention. In effect, their dynamic systems must be disrupted as they
explore different ways of placing attention and processing information.
Limited attention requires movement preparation and alertness
Even with effective attention skills, there remain situations capable
of overtaxing our attention and information processing resources,
particularly when time to prepare for movement is limited. When these
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resources are taxed we react and respond slowly, movement quality
suffers, and our movements may be inappropriate. Consider, for example,
a driver waiting at a traffic light. The light turns green and the driver
carefully begins the move from brake to accelerator, but is startled by a
honk from the car behind. Attention is shifted away from scanning the
road and placed on a possible road-rage incident. The driver responds with
a hard step on the gas and fails to place attention on the typical relevant
information, like cross traffic and pedestrians. The driver hits a pedestrian
who was slow to cross the street, all because of unexpected circumstances
lead to attention switching and a poor movement choice. The poor choice
was made because the driver did not have the time to prepare the
movement fully. This scenario illustrates that movement preparation in
addition to attention is vital for better movements. So, how can be best
prepare for making movements?
Movement Preparation Strategies in Time-Constrained Situations.
Most sports, and many activities of daily living, are constrained by time
limits or require a fast reaction. Movements in these contexts are made
quickly following a stimulus or must proceed in rapid fashion to be
effective, and thus require a rapid preparation time. Put differently, how
can we make reaction time faster by speeding up sensory processing and
movement planning? There are eight strategies for doing so: (1) Use
warning signals, (2) Choose a sensory versus a motor set, (3) reduce the
number of choices, (4) Make the stimulus predictable, (5) Make the
stimulus compatible with the response, (6) Reduce response complexity,
(7) Increase alertness, and (8) Practice information processing. Each of
these is discussed below.
Warning signals come before the actual stimuli and do more than
just increase alertness or focus of attention. An appropriate warning signal
gives the individual advance notice (anticipation) on an upcoming
stimulus and/or response choice, which enables movement planning to
begin before to the actual stimulus. The optimal warning signal timing
varies with a task and signals arriving too early or too late may actually
slow reaction time and hamper movement quality. In addition, sometimes
the warning signal itself may give false information about an upcoming
stimulus. Altering the warning signal – or giving a false signal – and
varying the warning foreperiod, are common techniques used by athletes to
fool opponents, such as quarterbacks manipulating the timing of their ―hut,
hut‖ cadence. Experienced performers have learned what warnings are
useful and those that are not.
Choose a reaction time or a movement time set alters focus and
processing speed. As we saw earlier, reaction time and movement time are
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not related. If one concentrates on moving fast versus reacting fast then
they have adopted a movement time set or motor set versus a strategy to
react fast (reaction time set or sensory set). Sensory set RT is faster than
motor set RT, but movements are often faster in motor time sets. Real
differences between the sensory and motor sets are dependent on the task
itself and the performer (e.g., expert vs. novice). Differences are more
noticeable in novices.
Reducing the number of choices speeds up processing. Preparing
for a response takes more time if there are more choices; either in what
stimulus to choose or what response to choose. These complex reaction
time situations can slow down information processing as well as
movement time, and thus eliminating the number of choices can speed up
response time on both ends. Reducing the number of choices can be an
explicit decision to only select certain cues or movement responses, or is
an implicitly learned phenomenon. Experts tend to use cues, particularly
situational cues, to anticipate or rank-order stimulus choices. For example,
a baseball batter uses game history and current game situations to narrow
down the potential pitch selection and location. A related issue concerns
two or more stimuli arriving in short succession to one another, each
requiring a different response. The second stimulus slows down the whole
process. This phenomenon is called the psychological refractory period
(PRP). The PRP is the time delay in which a planned response is delayed
while another is being carried out – even if the tasks are different. The
PRP is one of the mechanisms by which faking a player works. The
defensive player must overcome the processing time of the initial fake
before they can respond to the real move.
Make the stimulus predictable speeds up processing. If the
stimulus is predictable, then the number of choices is reduced, resulting in
faster and more accurate responses. Stimulus predictability is an
important factor in anticipation and the use of warning cues. For example,
if a person's eyes look to the left (a warning), then they are more likely to
move (moving is the stimulus) to the left. Predictability leads to an
expectation bias – we lean towards looking for a particular stimulus or
plan on a particular response. Note, however, if our expectation is wrong
then our response time is slowed. If the warning interval is predictable the
stimulus becomes more predictable.
If the stimulus is compatible with the response then processing
time is faster. Stimulus-response (S-R) incompatibility not only makes for
slower RTs but there is more likelihood of a movement error. For
example, a movement made to the left is slower if the stimulus is on the
right versus a stimulus on the left. S-R compatibility is not always so
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simple and sometimes non-compatible S-R situations must be practiced to
make them compatible. A rear wheel skid while driving is one such
situation that through practice a non-compatible S-R is made compatible.
During a rear wheel skid, as on icy roads, the rear end of the vehicle slides
out to the left or right. There are two seemingly compatible responses; one
is to brake and the other is to turn the steering wheel away from the
direction of the skid. Both are bad choices. The best choice is to not brake
and turn the wheel (i.e., front wheels) into the direction of the skid. Novice
drivers are confused by this, but when told to keep pointing the wheel in
the direction they want to go it becomes a much more compatible
response.
Reducing response complexity speeds up information processing.
The more complicated the response, such as a movement with many parts,
the longer the RT. This is one of the few times that reaction time and
movement time can be affected by the same thing. Reducing response
complexity has much to do with making movements automatic.
Alertness is defined as a high mental readiness for action, or high
level of vigilance. Attention skills rely on alertness, and without alertness
our ability to detect and interpret stimuli is slowed. Many physiological
factors hamper alertness, like fatigue and health, but maintaining alertness
in most activities is a conscious effort.
Practicing information processing affects each of the proceeding
factors. Plainly put, with more practice come faster RTs and better
movements. This is especially true in complex movements or situations
with multiple RT choices. Practice influences the other seven factors by
enabling the individual to make use of warnings, choose a motor or
sensory set (or combine them), reduce the number of choices, and reduce
situational complexity and uncertainty. Practice also helps the learner
synthesize important information so that anticipation can be used.
Synthesizing information is part of the interpretation/perception process
and helps plan tactics. When tactics or strategies to particular stimuli are
known in advance, the resultant response can be carried out faster and
more accurately. For example, an expert tennis player runs down a ball and
hits a forehand drive down the line to the opponent playing at the net. The
player must either hold ground to await a volley back down the sideline or
quickly reverse direction to get ready for a cross court or drop volley. The
player can anticipate and respond to what they think will happen, or they
can react to the opponent. Either way, the player's experience with the
opponent (tendencies, weaknesses, etc.), knowledge of their own
capabilities and understanding of the particular circumstances (e.g., how
off-balance am I?), allows them to prepare and carry out the response
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better and faster. It has been suggested that mental practice to plan tactics
to particular events can help speed up processing during actual events
(Vealey & Greenleaf, 1998).
Non-speeded movements also require attention and information
processing
Not all movements require fast reactions and fast movements.
Nevertheless, purposeful movements still need preparation that requires
information processing time. Our earlier discussion of the speed-accuracy
tradeoff well illustrates that finely controlled movements require a great
deal of information processing. Consider the simple act of writing a letter.
The movement starts with reaching down for a pen. There is no need for
rapid movements or reactions, but processing time is taken to decide on
the pen and how to reach for it. Visual search for a pen (or a reliance on
kinesthesia if a pen‘s location is already known), and decisions on how to
pick it up must be made (e.g., in the correct finger position, or will the
correct finger placement be made after the pen is picked up?). In this case
the research evidence suggests that decisions are made by ensuring that the
final movement outcome will place the arm and hand in the most
comfortable position. Thus, an awkward movement might be initiated so
that when the pen is brought to the final position on the paper it is
comfortable and ready to go.
Attention control helps control arousal and overcome stressful situations
Among the most common disruptors of effective information
processing are too much stress and too little stress. Stress is defined as the
physiological and psychological changes that happen in response to
changing conditions. When stress levels get high, particularly
psychological stress, resources are challenged and distracting negative and
irrelevant thoughts are common. Too much stress may contribute to
anxiety and nervousness which exacerbates the resource loss. On the other
hand, too little stress, which may be seen as a highly relaxed state, may
result in low arousal levels that then decreases alertness and attentional
focus, and may lower resource capacity.
Manipulating Stress and Arousal. Arousal refers to the activation
level of the emotional, mental, and physiological systems. The arousal
level, before and during motor performance, affects movement quality and
movement preparation time and is commonly manipulated by athletes and
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non-athletes alike to get into a state of readiness. Arousal can be lowered
through relaxation methods or increased by ―psyching up‖ methods.
Stress and arousal should not be confused. Under high states of
stress the body and mind may become highly aroused, such as during a
fight or flight response. Stress may be accompanied by arousal of systems
that can impede motor skill performance, like distracting memories and
emotional thought patterns. Alternately, sometimes the response to stress
can be to shut down mental and physiological systems, resulting in
physiological and psychological lethargy. For optimal motor skill
performance it is necessary to overcome excessive levels of stress and
manage arousal to levels that are optimal for action and information
processing.
Two factors need to be taken into account regarding the optimal
level of arousal for motor performance. They are the (1) motor skill type
and the context under which the motor skill is performed, and (2) level of
arousal of the performer.
Different motor skills and different situations may require different
levels of arousal. For example, football linemen tend to be more aroused
than golfers. The optimal level of arousal for a given skill is related to the
quantity of things that need to be done and the complexity of what needs
to be done. Generally, if a task is more complex, then less arousal is
necessary. But the level of muscular activation must also be factored in.
Higher levels or arousal may enable a higher level of neuromuscular
activity, and thus force output. But, individuals can learn to keep mental
arousal while maintaining neuromuscular relaxation if that is what is
necessary.
The optimal level of arousal for the performer to match the
movement situation is individual specific, but for each individual there
appears to be levels that are too high and too low. The relationship
between performance and arousal is shaped like an upside-down U.
According to the inverted-U theory of arousal, at very low and very high
levels of arousal performance suffers. The specifics of this theory have
been debated and refuted, but it does appear that there exists an optimal
level of arousal for a particular skill, which is dependent on several factors
discussed below.
Arousal and anxiety level of the
high
individual can be dependent on the situation
p erformance
where the skill is being performed. In general,
level
the importance of the situation and the
uncertainty of the situation increase performer
low
low
arousal, even to a state of anxiety. In these
arousal level
high
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cases the level of arousal may be excessive for the situation, and if stress
and anxiety are involved, then irrelevant
Individual differences in arousal responses are
or negative resources may be aroused.
nicely illustrated in research by Noteboom and
Individual differences in arousal and stress his colleagues (2001). These authors found that
steadiness on a pinch force task declined
are noteworthy.
following arousal by electric shock but not by
Attention Control and Arousal.
arousal from doing math problems. Subjects in
this study had to maintain a constant pinch
Extreme arousal or anxiety can reduce
force, but when electric shock (or threat of
attentional capacity and can distract an
shock) increased arousal (determined by
individual with "bad thoughts." Consider
physiological signs like heart rate and blood
pressure) their steadiness got worse. When
an experiment by Gage et al. (2003), who
―forced‖ to do difficult math under time
had people walk on a normal surface and
constraints the arousal increased just as with the
on an elevated walkway that created a
shock, but motor performance on the pinch force
steadiness test was only minimally affected.
falling threat and anxiety. Physiological
Women‘s performances were more affected by
data from galvanic skin responses
the arousal than men‘s. Can you interpret these
indicated anxiousness during elevated
results?
walking. During walking the subjects had
a reaction time task to respond verbally to a buzzer. As the threat
increased, reaction time slowed, indicating that anxiety took attention
resources away from anticipating to the buzzer. Walking also slowed
under the threat, showing the effects of anxiety on movement. Walking
could have slowed due to the subjects being more careful (speed/accuracy
tradeoff), and/or because attention was also drawn away from walking
(walking does require attention resources) in addition to buzzer
anticipation. Either way, anxiety reduced attention to the important tasks,
resulting in slower reactions and slower walking.
This experiment demonstrated that performers may need to reduce
attention demands by either reducing the width and direction of focus. It
is most common to narrow the focus to place attention on the most
immediate and pressing needs. The performer may need to select a
particular item to attend to and focus narrowly on it. Unfortunately, a very
narrow focus may not be desirable for performance, especially if many
environmental factors need to be scanned for cues, such as all the players‘
actions on the basketball court. In addition, some internal cues (e.g.,
thoughts, plans, activities, sensory info) that are desirable for good
performance may be ignored when the focus is too narrow.
Training and practice can help one to learn to focus attention,
select appropriate cues, and be able to switch attention. It might seem that
relaxation training is a good way to overcome anxiety and therefore
eliminate the need to rely on a narrow focus. However, relaxation training
is essentially practice of focusing attention on relaxation. Unless it is in
some sort of rehabilitation or clinical setting, having attention placed on
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relaxation takes away from attention on the important task at hand, like
shooting the free throw, selecting a good pitch to hit, and so forth. The
point is that relaxation training may not be effective unless attention
control to the goal of the task is also practiced.
Intention and Effort and Attention
The importance of attention control cannot be overstated. The
nature and quality of our attention contributes directly to the quality of
motor performance and the physiological adaptations that arise from
motor performance training. Attention skills are among the first motor
learning skills that should be emphasized to learners, having an impact on
most every other aspect of motor performance. Attention skills, however,
do not stand alone. Useful attention skills cannot be learned or carried out
with intention and effort.
Intention provides purpose and direction
Intention is primarily a psychological process; it provides a goal or
a plan of action that includes the what, why, and how of a movement. On
a large scale it provides a purpose and an outcome goal for training or
practice. Intent can include easily identifiable goals like overcoming a
specific deficiency or improving relaxation while shooting free throws.
Intention can also include very specific physiological outcomes, such as
training to cause maximal motor unit activation. Intention provides the
larger reasoning or rationale for doing acts. For example, a child may have
motor activity goal to ride a bike, but the intention may be either to escape
bullies or go to the store. Without a specific purpose, meaning and
importance are lost and knowing where to place attention becomes
uncertain. In previous sections the importance of a movement being
meaningful were highlighted. Intention also gives rise to how a plan is to
be accomplished. Part of this is technical, for example, practice scheduling
and using specific biomechanical techniques.
To illustrate, consider a competitive time-trial cyclist. Of course
the cyclist wants to get better, but what will it take to do so? Should the
cyclist go out every day with maximal effort in order to fatigue her
physiological systems? Perhaps, but it might be a better idea to have the
intention to ride on the cusp of the anerobic threshold for as long as she
can in order to better force a shift in the threshold value. Or, she could
focus on rhythmic breathing and consistent velocities in an attempt to train
efficiency. Either option may differentially train inter or intramuscular
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coordination. Alternately, she could hop off the road bike and engage in
specific resistance training designed to improve force sharing among the
hip flexors and among the hip extensors.
Effort must be intentional
Another part of the intention process has to do with effort and
motivation (these terms are not the same). In other words, how much
effort one decides to give must be planned, especially if the effort required
is maximal, as is often necessary. Effort is often erroneously considered to
be mostly a physiological term, meaning how much time and energy one
devotes to the task, and how much vigor one puts into practice or training.
Yet, psychological effort must come before physiological effort.
Preparation, cognitive effort, alertness and arousal, time taken to plan
training, studying game films — all these require a degree of mental effort.
Concentration requires mental effort. Overcoming fear or anxiety requires
mental effort. Without full mental effort during practices or games one
may drift off, loose attention, and motor performance suffers.
In summary, intention gives rise to purposeful effort, and both set
the foundation for effective attention. Maintaining intention, effort, and
attention on a short term basis (e.g., one game or week) may be simple, but
the outstanding performers do month after month and year after year.
Summary and Applications
Information processing was defined as the essential the job of the
central nervous system. Taking in information, interpreting and making
sense of information, storing, categorizing, and recalling information, and
making decisions and executing plans are all part of the brain‘s role. The
brain, however, is limited in its ability to process a lot of information or
simultaneously process multiple types of information. Memory was seen
as an important resource that factors into high level performance and is
one cognitive processing resource with clearly identifiable strategies for
improvement. One of the memory strategies is to make movements
meaningful, which also plays a role in attention and intention.
Attention control is the most important way to regulate resource
use and may be the best first strategy to use to improve the information
processing aspects of motor skill performance. Knowing where to place
attention, the quality of attention, and the ability to switch attention
dictates the amount and type of information being received by the CNS.
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Attention control is also necessary to control stress and arousal in sport
settings.
Underlying attention control is intention. Without the proper
intention our selective and focused attention are uncertain, and our ability
to maximize mental and physical effort is limited. Intention serves to filter
the incoming information and provides purpose to outgoing commands.
Intention not only modifies attention and effort, but in doing so directly
influences the nature of physiological performance and physiological
adaptations arising from training and practice. Put differently, intent and
effort influences motor unit recruitment and other characteristics of
intramuscular coordination, dictates muscle activation schemes for whole
body coordination, and motivates us. The take home message is that all
training and practice, from individual exercises to year-long plans, must be
intentional for maximum benefits.
Bibliography and Other Sources
Bernstein N. (1967). The Co-ordination and Regulation of
Movements. Oxford, England: Pergamon Press.
Gage, W., Sleik, R., Polych, M., McKenzie, N., & Brown, L.
(2003). The allocation of attention during locomotion is altered by anxiety.
Experimental Brain Research,150(3), 385-394.
Noteboom, J., Barnholt, K., & Enoka, R. (2001). Activation of the
arousal response and impairment of performance increase with anxiety and
stressor intensity. Journal of Applied Physiology, 91(5), 2093-2101.
Vealey, R.S. & Greenleaf, C.A. (1998) Seeing is believing:
Understanding and using imagery in sport. In J.M. Williams (Ed.), Applied
sport psychology: Personal growth to peak performance (pp. 237-269).
Mountain View, CA: Mayfield Publishing Company.
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CHAPTER 8
ABILITIES AND INDIVIDUAL
DIFFERENCES
Chapter Outline
I. Determining Abilities
II. Talent Identification
III. Summary and Application
f there is one thing that characterizes people, it is that we are all
different. People come with a vast array of qualities that alone or
in combination provide each with unique abilities. These abilities give rise
to different skill sets and proficiencies, which enable people to solve
problems and overcome challenges in vastly different ways. Two football
running backs, for example, may be equally successful (yards gained per
carry), but one gains yards by avoiding tacklers while the other runs
through tacklers. The first running back may rely on abilities like agility,
perceptual decision making, and visual search. In contrast, the second
running back may make use of leg power, body mass, and an aggressive
personality.
Both runners in this example use motor abilities that contribute to
their running skill. There are many such abilities, some of which are easily
identifiable, some of which are difficult to identify, and some of which are
clearly yet to be known. This is just one of the problems in trying to
identify the essential abilities that underlie successful motor skill
performance, or for identifying athletic potential in individuals. In this
chapter we will first look at the nature of abilities, how to identify them,
and the problems with using abilities to predict future motor skill success.
I
Determining Abilities
Physical proficiency abilities are the simplest to identify
Abilities that have been identified fall into three broad categories;
(1) physical proficiency, (2) psychological, and (3), psychomotor. Physical
proficiency abilities are those that are based largely on physiological and
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anatomical characteristics. These abilities include those that are highly
modifiable through training, such as muscle strength, muscle mass,
flexibility, maximal oxygen uptake and metabolic properties, stroke
volume, body weight, and running speed. These abilities also include those
that are unchangeable or minimally changeable, such as muscle fiber type,
height, bone and tissue strength, lung size, and many others. Keep in mind
that some of these abilities are largely genetic and others are highly
influenced by training.
Physical proficiency abilities are often simple to identify either
through direct observation or testing. Indeed, physical proficiency and
physiological measures form the majority of testing across the range from
athletic performance to medical testing in unhealthy persons. Strength,
speed, power, and metabolism form the bulk of athlete testing, and
measures like heart rate, blood pressure, and blood tests are just a few of
the basic measures taken in nearly every medical evaluation.
Psychomotor and psychological abilities are more difficult to quantify
Psychomotor abilities are physical proficiency abilities that require
a great deal of cognitive processing. Generally, this includes movements
with a large accuracy or precision component, hand-eye coordination,
reaction time, or motor decision making. Psychological abilities are
numerous, but their contributions to successful motor performance are
much less clear compared to physical proficiency abilities. General
psychological abilities that have been identified as important in many sport
situations include motivation, desire and enthusiasm, concentration, selfefficacy and confidence, task-related information processing, and
hardiness. Other cognitive abilities with an uncertain relationship to motor
performance, or that may vary depending on the motor task, include
general intelligence, emotional coping, aggression, personality, and hope.
Though some psychomotor abilities, like reaction time, are easy to
measure in the laboratory, the validity of these measures to contribute to
real-life and sporting environments is often uncertain. Psychological
abilities, generally measured by pen and paper tests, are plagued by
validity and reliability issues, which is one reason why only a few
psychological abilities have been decidedly identified as important.
Unlike the physical proficiency abilities, the genetic predisposition
and trainability of the psychological and psychomotor abilities has been
little investigated. Moreover, the psychological factors that give rise to
psychological abilities, for instance, identifying psychological traits that
enable one to gain more sport related information processing, are largely
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unknown. Despite the cloud of ambiguity that surrounds the identification
and measurement of psychological abilities, there is a growing recognition
that psychomotor and psychological abilities are the key to performance at
the highest levels. For example, even a simple agility test with a reaction
time component (perceptual motor open skill) is a much better
discriminator of higher level athletes than a simple closed skill agility test
without the reaction time component (Sheppard et al., 2006).
Visuomotor Ability. Vision plays the crucial role in many motor
skills, particularly open skills involving the need to monitor the external
environment. Vision plays a considerable role in feedback, but more than
any other sensory system plays a role in movement preparation, that is,
feedforward. In particular, visual search enables the performer to
anticipate and pre-select and pre-set limb and body movements relative to
the environment.
Vision, like other sensory systems, involves both a physiological
detection component and a ―software‖ perception component. The
hardware is composed of the eye itself. Eye function is relatively easy to
examine, generally with acuity tests (e.g., 20/20 on the Snellen eye chart),
color vision, focal vision (about 2-5 degrees), and peripheral vision (about
200° horizontal and 160° vertical). It was thought that 20/20 or better
vision was a prerequisite for any hand-eye coordination sport, and that
these types of athletes had better vision than the general public. This,
however, is not likely the case. Certainly there are reports of athletes with
better than average vision, such as the 20/10 vision of Hall of Fame
baseball player Ted Williams. Williams, however, dismissed this as being
the important factor in seeing the ball, but rather, he maintained that it was
his intense discipline and visual concentration that was important.
Williams‘ comment supports the growing body of evidence that
visual processing is more important than pure acuity. In sport, for
example, visual search strategies and pattern recognition enable the
performer to find and interpret information enabling them to anticipate and
prepare for a response. Anticipation reduces reaction time and enables
more efficient and more appropriate movements. Another component of
anticipation is anticipation timing. Anticipation timing is when an
individual begins whole body or limb movements in accord with an
external reference, often for an interceptive action. For example, timing
the baseball swing to meet the pitch or timing a pass to meet a moving
player are common uses if anticipation timing.
Anticipation, though, uses more than just timing and visual
information. Consider a softball outfielder getting a jump on the ball. She
may begin moving even before the ball is hit because she anticipates where
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it will be hit. She can make this educated judgment because she picks up
information on the type of pitch (slow, fast, curve, etc.), the location of the
pitch (inside or away from the batter), the timing and speed of the pitch,
the biomechanics of the batter's swing, and integrates all this with her
knowledge of the batter's tendencies (e.g., pull hitter) and softball physics
(e.g., slow pitches more likely to be "pulled", outside pitches more likely
hit to the "opposite field"). As a result she anticipates the most likely area
for the ball to be hit and begins running there before it is hit.
Visual sensation is genetically linked, but is visual perception also
genetic? Is it possible to improve both sensation and perception of vision?
There is not a lot of evidence that experts in a chosen field have better
sensation (e.g., acuity, focal and peripheral vision), nor is there compelling
evidence that better visual acuity can be improved with visual training. It
is well known that experts have better visual search, and growing evidence
that visual search is modifiable through training. Exactly how much one‘s
visual perception can improve, though, is unknown.
Motor skill proficiency requires many abilities
Successful motor skill performance, whether driving, knitting, or
playing linebacker, nearly always requires multiple motor abilities. The
contribution of some abilities to performance seems obvious, like vertical
jump height to basketball playing. Yet, the importance of a particular
ability to performance varies considerably among individuals. Basketball
Hall of Famers Larry Bird and Magic Johnson had only average jumping
ability by NBA standards, yet along with Michael Jordan (outstanding
vertical leap) were the stars of their day. Bird and Johnson used other
abilities – court sense, knowledge, shooting touch, body control – to gain
success on the court.
There are a few athletes that seem able to ―do it all.‖ The
performance of multiple sport stars, like Jim Thorpe, Babe Didrikson
Zaharias, and Deion Sanders, seem to imply the existence of a singular
global motor ability that contributes to ultimate motor skill performance.
In other words, is there some motor ability that is required for success in
any sport, or in any given sport is there some ability that all the successful
athletes have? The answer to the question appears to be a resounding
―no.‖ Research extending back to the 1950s has been unequivocal in
documenting that success – even high level success – in one sport or motor
skill does not in any way guarantee success in any other sport or motor
skill.
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The all-around athlete is best explained by an athlete having many
abilities or a few extremely good abilities that are relevant to many skills.
For example, power, speed, and visual search are abilities that are
important to many sports, and some athletes manage to exploit these
abilities and transfer them to other sports. This does not mean that any
athlete with these skills can easily apply them across the board, not does it
imply that there is a general motor educability, that is, a general ease to
learn new skills.
Talent Identification
It makes sense that if one‘s motor abilities can be determined, then
practice and training can be more deliberate in enhancing strengths and
overcoming weaknesses. Moreover, it seems reasonable that prediction of
motor performance proficiency would be possible if one‘s underlying
motor abilities were identified. Both of these suggestions have merit, and
both are widely practiced. However, there are a number of issues that
make teaching and prediction based on motor abilities difficult.
Determining abilities for practical use is difficult
The first issue is the measurement of one‘s abilities. As we saw
earlier, some abilities are difficult to measure or even categorize. The
second issue concerns the matching of one‘s abilities with performance in
a particular motor skill. There have been numerous studies that have
identified certain features of athletes participating in certain sports. The
best hitters in volleyball, for example, tend to have good vertical leaps and
be tall. There are many players, though, that are tall with good vertical
leaps that are not good hitters. Abernethy and his colleagues noted that
muscle strength is able to discriminate players in many sports, but only to
the extent of identifying high level from low level athletes. Within a
performance level (e.g., NFL) strength does not appear to discriminate one
athlete from another. These examples illustrate the difficulty in identifying
the essential abilities necessary for good performance and that individuals
bring their own ability mixture to motor skill performance.
The widespread use of talent identification in children does not have
research support
Prediction of future performance based on current abilities is
widespread, and is often referred to as talent identification. Talent in this
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context is defined as the combination of skills and abilities contributing to
overall success in sport or other activities. For example, personality tests,
like the Myers-Briggs Inventory, are used in business to assess the
qualifications and potential for success for managers. The NFL
participates in the ―scouting combine,‖ a four day series of physical and
mental proficiency tests to rate the potential for college players to succeed
in the NFL. Perhaps the most striking example of talent identification is
the selection of children by the Chinese to enter their Olympic training
programs. In China, talent selection officers travel from elementary school
to elementary school and measure flexibility, reaction time, body and bone
anthropometrics, and other abilities. Children with outstanding abilities are
sent to sport training schools specific to their abilities, like gymnastics
school for children with high flexibility or weight lifting school for
children with specific leg to torso to arm length ratios. While the Chinese
authorities may marvel at this model of efficiency, there is little evidence
that such a selection process has merit. Vaeyens and his colleagues (2009)
have looked Olympic talent identification programs and concluded that
they remain questionable, and further, noted that the extended institutional
sport specific training for adolescents is not necessarily associated with
elite sport achievement. Even the validity of the highly touted NFL
scouting combine is questionable (Kuzmits et al., 2008). In all cases,
particularly the testing of children and adolescents, fail to adhere to the
two known principles of prediction; 1) Identifying the essential abilities of
the target skill, and 2) The validity and reliability of the tests used.
Talent identification may aid in domain selection
Identifying the essential abilities of any motor skill is difficult,
particularly as the motor skill becomes more complex. As described
above, individuals may achieve high levels of success even with abilities
that do not seem characteristic of the sport or activity. On the other hand, it
is possible to identify abilities that contribute to domain selection. For
example, short individuals may be drawn toward activities in which a
slight stature is a definite advantage, such as gymnastics or horse riding.
Individuals with a large percentage of fast twitch muscle fibers may avoid
aerobic type activities. Domain selection, whether done ‗forcibly‘ by the
government or by one‘s own volition, may have a large genetic component
and may serve to eliminate activities rather than select specific activities.
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Predicting motor skill success from abilities is problematic
Domain selection aside, it is challenging to predict later success
from early achievement in children or in novice performers. Generally,
initial success (good or bad) does not predict future performance, because
the abilities for success at an early stage are often different from those at a
later stage. As performers go through learning stages they must acquire or
make use of new abilities. For example, strength is a strong predictor of
high school wrestling success, but not so at high levels such as Olympic
level wrestlers. Though predicting growth and height is reliable, maturity
and adaptability to practice and training are not. For example, there is no
way to assess a child‘s capability for strength development.
At this time, the evidence points to one factor that may contribute
to success in many sports or activities. This factor is relative age, and it
simply means that the older children within an age group will be more
likely to succeed at each age progression. It is thought that these children
are bigger and more mature than their counterparts, which are clear
advantages at an early age. These advantages contribute to more success,
and because of this success more time and effort is provided to these
children. Moreover, this early success is a strong motivator for these
children to continue to participate and work hard for more success. Mujika
et al. (2009) described this bias as a loss of a lot of potential talent.
Ability testing does have some merit
Given the problems and pitfalls of measuring abilities, is there any
reason to measure them? The answer is yes, because measuring abilities
provides a metric upon which the effectiveness of practice, training, and
rehabilitation may be evaluated. Knowing the abilities that seem to
characterize the athletes in certain sports provides at least some direction
for individuals regarding training and practice and domain selection.
Summary and Application
Individuals have a wide array of motor abilities that alone or in
combination provide the basis for successful motor skill performance.
These abilities include those that are physical proficiency, psychomotor,
and psychological. Though some abilities have been clearly identified as
major components of success in specific motor skills, determining the
essential abilities for most all motor skills has proved difficult. What is
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clear is that individuals can succeed at particular motor skills with
different combinations of abilities.
This does not imply that any motor skill activity can be
accomplished with a high level of success with just any combination of
abilities. Some abilities help discriminate potential activities through
domain selection, either by providing a clear advantage or disadvantage.
Aside from domain selection (though it too is questionable), attempting to
predict a child or novice performer‘s later motor skill success based on the
evaluation of abilities is filled with problems. There are simply too many
factors involved with motor skill success to take stock in measuring just a
few motor abilities, even in those cases where the abilities testing is
reliable and valid.
Ability testing does have it uses, however. It is well understood
that for many sports and motor skills there is a base or minimal level of
abilities, such as strength, speed, body size, visual acuity, and so forth, that
empirically and theoretically contribute to performance. These measures
provide minimal goals for individuals to strive for during practice and
training. Measurement of abilities also helps identify overt weaknesses and
strengths, and provides measurements upon which progression may be
monitored during training or rehabilitation.
Bibliography and Other Sources
Abernethy, P., Wilson, G., & Logan, P. (1995). Strength and power
assessment. Issues, controversies and challenges. Sports Medicine, 19(6),
401-417.
Adams, A. J., & Kuzmits, F. E. (2008). Testing the Relationship
Between a Cognitive Ability Test and Player Success: The National
Football League Case. Athletic Insight, 10(1), 5.
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CHAPTER 9
INSTRUCTION, PRACTICE, AND
TRAINING
Chapter Outline
I. Basic Concepts in Instruction
II. Feedback
III. Practice Organization
IV. Mental Practice
V. Putting it All Together: A Model of Practice
VI. Creating the Environment for Practice and Training
VII. Summary and Application
t the heart of motor learning are instruction and practice.
Regardless of one‘s abilities, motor skill proficiency can best
– or only – be attained through dedicated and purposeful practice or
training. Practice is differentiated from training only in what is targeted for
improvement. Practice is aimed at improving mental performance, tactics,
strategies, team play, and motor skills. Training is aimed at improving
physiological functioning and physical proficiency abilities. Though the
principles presented in this chapter are generally referred to as practicerelated, they apply equally well to training.
There are two components to practice, the learner and the
instructor. In the last chapter we looked at characteristics of the learner. In
this chapter we emphasize instruction and the integration of the learner
with instructional methods, that is, practice.
A
Basic Concepts in Instruction
Modeling is the most common, but is often overused and misused
The most common method of instruction, particularly for new
learners, is modeling, otherwise known as demonstration or observational
learning. In modeling the instructor demonstrates the skill to be learned
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and the learner then mimics the skill. The effectiveness of modeling is
related to (1) who models and (2) the type of skill being modeled.
Modeling is generally more effective with proficient and prominent
modelers. Not only is the demonstration more likely to be correct, but
learners are more likely to pay more attention and ascribe meaning to what
is being learned. It may be, however, that the expert model is too good,
confusing novice learners by the complexity of the movement. It can be
useful to have learners observe other novices learning a motor skill. The
observers pick up strategies that work and do not work, and in doing so are
engage in problem solving to a much greater extent than simply observing
an expert model.
Not all motor skills can be equally well modeled. During
observation of the motor skill, the learner‘s visual system picks up
coordination information, relative information such as timing and
sequencing of events. Thus, modeling works best for new skills or other
skills where gross coordination patterns are needed over precise control. If
precise control factors are needed and basic coordination patterns are
already established, then modeling may not be effective.
Auditory modeling, in which sounds accompany the movement,
can aid in observational learning. Auditory modeling is particularly useful
when precise timing of sequences is involved, and can provide a verbal
labeling to important components of a skill. For example, many people
make low level grunting sounds during striking tasks (e.g., hitting a ball)
that crescendo into a full grunt or yell at the moment of impact.
Observation has direct neurological consequences
A growing amount of evidence points reveals that a visuomotor
neuron system is activated when movements are observed. This system,
the motor resonance system, acts differently depending on the motor
actions being observed. The system is less active when observing nonhuman actors, or when the movement is impossible, or when the observer
is entirely unfamiliar with the task. When the motor resonance system is
active it appears to have four main functions for the brain; (1) to
understand the action, (2) understand the intention, (3) to enable imitation,
and (4) to understand behavioral state. In other words, parts of the motor
system are active when watching motor behaviors in order to help the
brain comprehend exactly what it is seeing, understand why (intention) the
movement is being carried out, to help the brain later imitate or mimic the
movement, and last, to help understand the emotions of the one being
observed.
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Regardless of the type of modeling, it appears most effective for
new learners or accomplished learners trying something new. Only limited
information on movements can be gleaned from observatoin, much of
which can be confined to the cognitive phase of learning.
Feedback
The role of the instructor is vital. Faulty learning, poor progress,
and reduced learner motivation are all potential outcomes of poor
instruction. Good instruction is accomplished through mastering the two
broad roles of the instructor; (1) feedback and communication, and (2)
creating the appropriate learning environment. Within each of these roles
are sub roles, such as mentoring, leadership, creating trust, technical
advice, and so forth. In this section the focus is on providing feedback and
creating a learning environment.
Feedback can be internal or external
Feedback (FB) is defined as information sent to the CNS
regarding any actions of body or mind. Feedback can come from internal
sources (e.g., proprioception) or external sources (e.g., coach). Internal
feedback originates from sensory receptors and may be visceral or somatic.
External feedback is information about performance that originates from
anything other than the performer‘s own sensory system. By definition,
external feedback is augmented feedback (AFB), because the source of
the feedback enhances, modifies, or simply makes known information that
the performer would not ordinarily receive. Augmented external feedback
is nearly always provided by an instructor, though current technologies
enable electronic instructors. Augemented sensory feedback, more
commonly known as biofeedback, is the use of electronic devices to
amplify biological processes to make them noticeable to the learner.
Common biofeedback devices include heart rate and blood pressure
monitors, respiratory rate monitors (pneumobellows), electrodermal
monitors like galvanic skin response devices, electroencephalography
(neurofeedback), and electromyography.
AFB provides knowledge of results or knowledge of performance
Augmented FB is given to (1) provide information concerning the
movement or physiological functioning, or 2) to provide motivation. In
either case, the AFB can be in the form of knowledge of results (KR) or
133
knowledge of performance (KP). Knowledge of results is information
concerning the movement outcome and knowledge of performance is
information about the movement characteristics that led to the movement
outcome. KP would include feedback such as verbal indication of arm
position during swimming, video assessment of leg position during
hurdling, or a graphical biomechanical assessment of gait kinematics. KP
is generally provided after the movement, but can be done during the
movement as well.
AFB may be important or detrimental to learning
Augmented FB in skill acquisition can be vital or not important to
skill acquisition, depending on the particular activity and the learner. Skill
acquisition can be hindered if the learner becomes dependent on the AFB
and thus performance drops when the AFB is removed. In these cases the
learner has not learned their own sensory cues and thus cannot respond to
them. AFB is very useful when the movement cannot be seen or if critical
sensory information is not provided or is unreliable. Faulty sensory
information is often seen in persons with injuries or certain disease states.
AFB is also important when sensory information is available, but is unable
to be used by the learner. This is a common feature in beginners who are
unable to recognize or interpret their own sensory signals.
In situations where the performance itself provides enough
information, the addition of AFB becomes redundant and unimportant.
This is most often the case when there is a detectable environmental
reference by which the performer can assess their performance. For
example, a basketball player does not need KR to inform them they missed
the rim on a free throw.
In brief, AFB can enhance skill acquisition under many
circumstances, typically in new learning situations or when one is
attempting to get off a plateau.
Giving useful AFB must take into account content, complexity, and
frequency
Augmented feedback can vary in its content, type, complexity, and
its frequency. All these factors can be varied to provide the best results.
Content of Feedback. Providing AFB should be based on several
factors: (1) The attention-direction of the FB, and (2) What part of the
movement gets FB. Note that these two factors are most appropriate in
early practice or initial learning sessions, which can include an
134
experienced performer learning a new technique. The attention-direction
content of AFB serves to help focus attention on that particular aspect of
the skill. If the AFB is too general then attention cannot be focused. Thus,
it is important to realize that the AFB, while not only providing movement
information, also serves to focus attention to a particular movement
component.
For KP especially, the skill must be broken down into most
important and least important parts, that is, the components must be
prioritized. Determining what aspect of movement receives AFB requires
an instructor with knowledge of the motor skill and knowledge of the
performer. Intuitively, it would seem that the poorest aspect of a motor
skill should receive feedback, but this is not always the case. Sometimes a
poor movement component is the result of glitches in prior components,
causing a sequential worsening of movement performance over the
progression of the movement. For example, poor ball control and shooting
during a basketball layup is often the result of uncoordinated footwork and
leaping. In this case feedback and instruction should be placed on
footwork, and not shooting. Generally, that part of the skill that will
significantly improve the entire skill is the best candidate for AFB.
Determining which aspect of movement should receive AFB also
includes whether AFB should be given on poor movements or on correct
movements. For example, an athlete performing a squat lift could be given
AFB regarding good back positioning or on poor knee range of motion. In
general, information on incorrect movement or errors is more effective and
should be used more, but both can and should
be used. Information on correct movements
These rowing stroke power curves illustrate
often has an advantage in that it can be more
different types of strokes and thus provide
feedback to the rower. The rower may then
motivating or confidence-inspiring, although
adjust the stroke to match the desired power
some people are more motivated by negative
profile.
comments.
Augmented FB can be descriptive or
prescriptive. Descriptive is a description of
what was done (can be qualitative or
quantitative) in the movement. Prescriptive is
providing information not on what was done,
but what needs to be done for a correct
movement. In general, novices need more
prescriptive, experts need more descriptive.
Types of AFB. Augmented feedback
comes is three main types, KP, KR, or sensory
biofeedback. Each type, however, can be
135
delivered in different ways. Verbal FB is the easiest and most common for
both KR and KP. Perhaps the second most common form of AFB,
particularly in exercise and sport science settings, is physical guidance.
The instructor physically leads the learner through the motion. This
method can lead to early success but may be detrimental to retention.
Thus, physical guidance can be used in early learning to acquaint the
learner to the task.
Video, such as game films or high speed biomechanical analyses,
is likely the third most used KP technique. Video KP effectiveness is
largely dependent on the performer's skill level and not so much the skill
itself. Beginners generally need verbal KP on top of the video, while more
experienced performers may be able to assess the important information
without other instruction. Video KP may provide a single revelation type
of moment for the learner, but it generally needs to be used for at least 5
weeks for most effectiveness. Other KP methods tend to involve high
technology, such as graphical displays of biomechanical information.
Biomechanical information, for example power curves during rowing
strokes, is probably best reserved for the most skilled performers. How
effective it really is somewhat speculative, even though it is growing in
use with affordable camera systems and user friendly software.
Among biofeedback KP, heart rate monitors to evaluate exercise
intensity are the most common, and are used in settings from cardiac
rehabilitation to high level athletes. Among other biofeedback devices,
only galvanic skin response (GSR) devices to monitor relaxation are
readily available to the lay person. In clinical settings, EMG biofeedback is
used to help determine muscle activation patterns in addition to
monitoring muscle relaxation. Other biofeedback methods include blood
flow and blood pressure, skin temperature, respiration, and
electroencephalography (EEG) for neurofeedback. Most of these are used
for relaxation techniques but can be used for other applications as well.
Complexity of Feedback. AFB can be highly complex and detailed,
or as simple as statements commenting as ―good‖ or ―bad.‖ Determining
the level of complexity begins with setting a performance bandwidth,
that is, the amount of error that prompts a feedback correction. In general,
beginners need a larger bandwidth or margin of error before AFB is
provided, and experts need a smaller bandwidth.
Instructors also need to consider if qualitative or quantitative AFB
is appropriate. Generally, quantitative AFB is better because it is more
precise, but the level of experience and practice time must be taken into
account. The novice needs, or sometimes can only use, simpler AFB such
as qualitative or simple quantitative. Qualitative AFB includes subjective
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statements such as ―Too slow,‖ or ―Not enough velocity.‖ With more
experience the AFB can get more complex and precise.
Frequency and Timing of AFB. It has been often suggested that
more feedback is better, but growing evidence suggests that too much
AFB is detrimental. Too much feedback could lead to 'memory overload'
or direct the learner to rely solely on the AFB as a crutch. In place of
constant feedback, competent instructors may give feedback summaries
after a specific number of trials or after a particular time period. In a
similar manner, giving FB that is not available during regular competitions
(such as practicing lifting techniques in front of a mirror; see Tremblay
and Proteau, 1998) could have detrimental effects on actual performance.
Eventually the learner will need to be weaned off the AFB. This can be
done by altering the performance or error bandwidth or by giving summary
feedback.
Augmented FB can be given during or after performance. During
performance this type of AFB is called concurrent AFB and should only be
used in certain circumstances. Concurrent AFB can be distracting, not only
when it arrives but as the learner anticipates its arrival. On the other hand,
sometimes it is useful to point out movement errors as they occur to enable
the learner to get a better grasp of the errors.
Most AFB is given after performance. The timing of the AFB
creates what is call the KR/KP delay and the post KR/KP interval. The
figure below shows that immediately after a performance trial, and before
AFB is provided, is a period of time known at the KR delay. After AFB is
provided is the post KR interval that precedes the next trial. The lengths of
these intervals should not be too long, but must be sufficiently long for the
learner to engage in activity after the movement (physical and/or mental)
with the intention to problem solve the task, such as figuring out what they
did right or wrong, or simply what they did.
tr ia l
conc urr ent
FB
AFB
KR de lay
next t rial
P ost KR
inter val
The post KR interval is the time after the FB is given and before
the next trial is done. The learner used this time to plan the next
movement, incorporating both the AFB and their own sensory information
into the next movement. If the KR delay is too short (immediate) then they
do not have time to problem-solve the integration of AFB and sensory
137
info. If the KR delay is too long the learner may forget either the AFB or
sensory info.
Practice Organization
Different motor activities require different forms of practice, but
there are several principles that apply across the board. First, it is
important to determine if motor skills need to be practiced as a whole
entity or broken down into constituent components. Second, variable
practice is generally more effective than practice aimed at a single skill.
Third, overlearning should be the target goal.
Motor skills can be simplified by parting them out
Most motor skills are not simple discrete acts, but complex
sequences of limb and whole body movements. In the case of complex
actions, it is generally better to break the skill down into its constituent
components and practice the components separately. This part practice
requires breaking down the skill based on the task complexity and
organization. In general, tasks low in complexity but high in organization
(the movement parts fit well together) should be practiced as a whole.
Tasks high in complexity, but low in organization, should be practice in
parts (e.g., tennis serve). In reality, skills lie in a continuum between
complexity and organization, and complexity and organization are often
defined by the learner.
Practice can be parted out in three main ways, (1) fractionization,
(2) segmentation, and (3) simplification. Fractionization is practicing
separate components of a whole skill. It is important to break the skill
components down into natural divisions. This method is helpful when
there are specific trouble areas that need working on. Segmentation (also
called the progressive part method) is practicing in sequences. For
example, if the skill has parts 1, 2, 3, then the method would be to practice
part 1, then 2, then 1 and 2 together, then 3, then 2 and 3 together, then 1
and 2 and 3 together. This method takes advantage of whole and part
practice. Simplification is perhaps the most common practice principle,
and involves stripping away the complexities of a skill and practicing the
essential and simplified version. Not all skills can be effectively
simplified, and doing so, as in the other part practice methods, requires the
instructor to have a strong understanding of the motor skill and how it can
be broken down.
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Regardless of the part practice method used, or if whole practice is
used, it is often useful to direct attention to specific components of the
motor skill. For example, if the ball toss in a tennis serve is the critical
element needing attention, the learner can be instructed to do the entire
serve but focus largely on the ball toss.
Variable practice enables better retention
Different motor activities require different forms of practice, but
there are several principles that apply under most circumstances. First, it is
usually more beneficial to practice a variety of tasks under a variety of
conditions (variable, random, or distributed practice) and avoid
practicing the same thing the entire practice session (constant or massed
practice). Variable practice which may cause an immediate performance
decrement, but generally leads to better acquisition and retention. It is
thought that variable practice forces individuals to switch attention better,
forces concentration, and is more specific to actual performance situations.
When done in a certain manner, variable practice promotes contextual
interference, in which practicing in one setting or context may actually
interfere with performance.
Variable practice can be illustrated by a golfer at the driving range
switching clubs every few balls, a baseball player seeing different pitches
every couple of pitches, or a football team offense practicing offensive
plays randomly as opposed to running the same play for 30 minutes
straight. During variable practice a basketball team may practice several
different offensive plays in random fashion, then move to shooting drills,
and then back to offensive plays. Performance during variable practice
may degrade relative to constant practice, but performance on retention
tests is generally better following variable practice.
This does not mean that massed practice does not have a place in
the practice environment, nor does it mean that all skills or all individuals
require the same types of variation in practice. It is important that the
instructor set up organized and purposeful practice situations to meet the
needs of the performer.
Overlearning is one goal of practice
Individual practice days and practice cycles (i.e., days, weeks, or
months) should be set up to get to a point of overlearning. Overlearning is
continual practice even past a point where performance seems to have
peaked. There is, though, a point of diminishing returns. In other words,
139
instructors need to balance out the cost (practice time) to benefit
(improvement) ratio. It is important to understand that the amount of
practice is secondary to the quality of practice.
Fatigue often accompanies effortful practice and training aimed at
overlearning. Fatigue, by definition, affects performance, but it does not
necessarily affect learning. If fatigue depletes mental resources and lowers
attention, then practice may be ineffective. In addition, if the fatigue is
task-specific and leads to faulty movement patterns, then it may be better
to avoid fatigue. For example, if one does an arm weightlifting program
before practicing free-throw shooting, arm and whole body coordination
may be poor – leading to learning improper coordination. However, if one
does the free-throw practice after running, and thus practices with leg and
'general' fatigue, then the practice may be like a real game situation.
Fatigue, thus, becomes a practice variable that may promote contextual
interference and better retention of motor performance. In general, learning
is better with shorter, more frequent, and better organized practice.
Mental Practice
Among the practice techniques found in high level performers is
that they engage in regular mental practice. Mental practice typically refers
to imagery techniques, but some authors also include relaxation and stress
control, positive self talk strategies, and concentration improvement as
components of mental practice. In this section imagery is described as one
mental practice technique and intention control as another. We maintain
here that essential mental practice includes the manipulation and control of
intentional thought patterns designed to influence the effectiveness and
outcomes of physical practice and training.
Imagery is used for skill acquisition and performance preparation
Imagery is most often thought of as the mental or cognitive
rehearsal of a skill, generally in the form of visualization (seeing the skill
in one‘s mind) or imagery (imagining multiple sensory aspects of the skill,
not just the visual). Imagery is by convention used as a general term that
we will use. Imagery is used for two general purposes, (1) skill acquisition
and (2) performance preparation. Skill acquisition typically involves the
learner modeling the motor skill in their own mind over and over again.
Learners may emphasize certain problem areas or emphasize the look or
feel of the movement, depending on what is meaningful to them. Imagery
140
without physical practice in only marginally successful, whereas physical
practice with imagery is generally better than physical practice alone.
Imagery used for performance preparation is either rehearsal for a
sequence of events (e.g., a gymnastics routine) or arousal modification.
Rehearsal may include going over the entire performance, as in seeing the
whole pattern of tactics and strategies during a game, or may emphasize
one particular point in a discrete skill, like ball contact during baseball
batting. It has stated that higher skilled performers use mental rehearsal to
see themselves winning or doing remarkable performances, but the
effectiveness of such ―glory‖ imaging in promoting high level performance
is questionable. Arousal modification can be some form of psyching up to
increase arousal or relaxation to lower arousal. Using imagery as a stress
control technique should include some form of problem solving, which is
one way to focus attention on important matters while reducing anxiety.
Whether using imagery for rehearsal or arousal, the result may be
enhanced confidence, anxiety reduction, and more focused attention.
Perspective, viewing angle, and sensory modality are varied during
imagery
There are three general characteristics that are a part of the imagery
process. They are the perspective (internal, external), the viewing angle,
and the dominant sensory modality (e.g., kinesthetic versus visual). In the
internal perspective the person views himself in the first person as he
would in real life. In the external, or third person, perspective the person
views himself from out of body. The viewing angle is what is actually
included in the mind‘s picture, for example, from the top or from the back
in a third person view, or the view of what the first person image is
looking at. Viewing angle appears to largely dependent on the motor skill
being imaged. The third factor in imagery is the dominant sensory
modality. Imagers tend to emphasize either visual or kinesthetic
information, even if sound and other sensory information is included
(sound is often included as a modality alongside the kinesthetic).
Regardless of which combination of perspective, angle, or sensory
modality is imaged, there is growing belief that ―agency‖ is critical to how
the brain is activated. Agency refers to the identity of the actual imaged
person. Imagers may see themselves or others performing. Even if the
imager is a first person of herself, if she puts herself in place of someone
else, then she may not be in full control of her action.
Holmes and Calmels (2008) summarized that identifying the best
way to image, or the imaging characteristics of expert performers, has
141
proven difficult due to methodological problems and the lack of consistent
results. In particular, image perspective, view, and agency, as well as
imagery clarity and vividness, may differ widely even in high level
athletes. These authors assert that imagery is generally so focused on the
precise motor behavior of the performer that the social context is lost,
which compromises the neural functional equivalence. Imagery scripts,
thus, must have contextual information with intent for the most
effectiveness.
Imaging has direct neurological consequences
Mental imaging of physiological effort has direct neurological
implications, that is, the same areas of the brain are active is similar
manners during imaging a task as when actually performing the task.
Magnetic resonance imaging and other brain scanning methods have
shown that real and imagined movements share a common physiological
substrate, but changing agency, perspective, viewing angle, and sensory
modality changes areas of the brain that are active. Some researchers have
shown that reflex excitability is increased when imaging a muscle or
movement, suggesting that thinking about movements causes a spinal cord
facilitory effect on muscle activation. Care must be taken in interpreting
these data, however, as the relationship between actual and imagined
movements differ between skilled and unskilled performers and with an
uncertain rationale for why. Holmes and Calmels (2008) cautioned that
brain activity due to real or imagined movements may not be functionally
equivalent.
Imagery and observation as practice methods
Holmes and Calmels (2008) suggest that observation of motor acts
provides a better practice tool than imagery. We suggest that observation
of motor acts before imagery puts the right context of imagery into place.
Observation activates the motor resonance system, thereby giving the
observer information on movement action, intention, and behavioral state
of mind. For example, observing opponents, and then imaging oneself
within the observation, theoretically takes advantage of the neural
substrates supporting both observation and imagery.
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Intention as mental practice contributes to neurophysiological adaptations
and improved physical proficiency
From the prior section it is evident that the characteristics of
imaging and observation activate the brain ways that are profound and
specific. These findings imply that to receive the desired physiological or
motor response that the nature of the mental activity should be specific
toward that response.
A number of studies support this view. Albeit somewhat
controversial, there are studies showing that weeks of mental imaging of
weight lifting improves muscle strength. Studies showing effective mental
strength training (Yue & Cole, 1992, Ranganathan et al., 2004) have used
a first person perspective with external focus imagery in which the
movement outcome, like moving an attached force transducer or lifting a
table, is the intention. Such improvements have been ascribed to better
central commands that are able to provide more activation and more
efficient inter and intra muscle coordination. The key finding from these
imagery studies is that the essential ingredient to the mental training is
intention.
Intention as the mental framework for physical practice leads to
better physiological adaptations. Consider the elegant experiment by
Behm & Sale (1993), who had
subjects perform ankle
max
dorsiflexion strength training
for 3 days per week over 16
weeks. One ankle was trained
Force
isokinetically at a fast speed,
the other ankle trained
isometrically. Under both
0
0
50
100 150 200 250 300
conditions the subjects tried, or
Isokinetic Speed (d/s)
intended, to do rapid ballistic
movements. The graph shows
that the isometric-trained leg did not improve isometric strength, but
rather, had the best improvement in high speed strength. Coinciding with
the power increases were increases in muscle activation speed, faster
muscle relaxation, and several other neurophysiological changes. These
results apparently violate the specificity of training principle in that the
isometrically trained limb had the least gains isometrically and the most
gains at high speed, that is, unless specificity includes the intent and effort
of the motor act. The authors concluded that the key training stimulus
appears to be the motor command and resultant motor unit activation
Post Test-Isometric
Post test-Isokinetic
Pre test
143
patterns associated with high velocity movements. Put differently, the
mind-set of the individual as revealed by movement intention, led to
measurable neurophysiological adaptations that were as important as the
actual physiological effort itself. In this way, mental practice should be
considered an equal partner with physical practice and training.
Putting it All Together: A Model of Practice
Given the guidelines for feedback, practice organization, and
mental practice, is there an overriding framework or model for designing
and conducting practice sessions? Current theories and approaches suggest
that the deliberate practice model proposed by Ericsson et al. (1994) is
the most effective and unifying model. We will discuss the deliberate
practice model, but first, we will examine two building block models that
begin to integrate instructional and practice features thus far discussed.
The first of these is Singer‘s 5-Step Approach and the second is
Discovery Learning.
The five step approach emphasizes mental preparation
Singer and his colleagues developed the 5-step approach to
learning and performing motor skills. The steps are (1) systematically
ready oneself, (2) image the act, (3) focus attention on a cue, (4) execute
without thought, and (5) evaluate the act and previous steps.
The most important aspects of this process are the focus of
attention and the execution without thought, which is also why this is
called the non-awareness strategy. For example Singer et al. (1993) found
the best learning when people do not think about how the movement
―feels‖ or do not pay attention to various other movement-related items.
When given a cue (e.g., center of the target to focus on) and then
instructed to ―just do it‖ the people learned better and faster and performed
the skill better. In a sense, the 5-step approach is attempting to force the
automaticity behaviors of expert performers. This strategy falls in line with
research demonstrating that an external focus of attention is much better
than an internal focus when learning and performing skills. The 5-step
approach fits within the deliberate practice model and also fits within a
discovery learning model discussed below.
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Discovery learning emphasizes individual control over learning
Discovery learning, or exploratory learning, is fundamentally
rooted in an individual trial and error approach to learning. It requires the
learner to search for optimal strategies to do a task, given the constraints of
the task. This process includes finding the best perceptual cues or
variables to produce motor responses that are specific to the environment
and task constraints, and fit within the individual‘s own physiological and
psychological makeup. Discovery learning, thus, fits precisely within the
dynamical systems theory.
Perceptual information can be descriptive or prescriptive, and can
be in the form of the individual‘s own sensory feedback or augmented
feedback. In order to effectively couple the body to the demands of the
environment requires solving movement problems. For example,
performers must analyze patterns of light and sound bouncing off
environmental surfaces to regulate movement timing, and must integrate
this information with vestibular, proprioceptive, and tactile sensory flow to
coordinate their body in the environment. According to discovery learning
theory, the learner must figure this out on his or her own. But how do they
do this? And is it necessary for an instructor to be involved?
In discovery learning explicit skills are not taught, but rather, the
learner is taught or led how to learn the skill by him or herself. The
instructor‘s role is very important in addition to being very difficult.
Instead of providing prescriptive instructions or precise modeling, the
instructor leads the learner through a progression of problems using
limited augmented FB in the traditional sense. One of the first strategies of
the instructor is to reduce the degrees of freedom and provide the optimal
environment to learn. Consider, for example, a child learning to walk. The
child sees the parents and others modeling walking, which encourages
them to walk and gives them basic movement ideas. In all likelihood,
watching others walk is not entirely necessary, in the same manner that the
infant does not have a crawling model when learning to crawl. The
parents‘ main role is to create a learning environment. Encouragement,
hand holding (reducing the degrees of freedom and provides confidence),
and encouraging walking on a rug (safety, good grip) are several ways
parents optimize the learning environment to encourage the child to
explore walking. The infant discovers for herself what movements she
should make, how to make them, why to make them, and the obstacles and
constraints to walking. Instructors, 'get inside' the learning situation to
uncover obstacles, but do not provide prescriptive FB. Prescriptive FB is
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only used to direct the learner's attention toward something important, or
to tip them off.
How is it that someone can learn skills without being told what to
do? With too much modeling and too much augmented FB, the learner
may divide attention between what the movement should look like or
should be (e.g., the form) and what needs to be done to do the movement
(e.g., forces, positions, etc.). With discovery learning the learner has no
preconceptions about the movement form and focuses attention on the task
purpose and meaning. During learning exploration the learner become
more sensitive to sensory FB and learns to interpret or understand it. In
addition, if one learns on their own, then they use the resources that they
have available rather than trying to copy someone else‘s techniques that
are based on that person‘s strengths and weaknesses.
How do we reconcile the concepts of exploratory learning with the
previous discussions of augmented FB and modeling of motor skills?
Discovery learning seems contrary to these concepts, and in some cases, it
is. We can reconcile and understand this information if we consider two
things. First, much of the specific information about providing augmented
FB and modeling was based on research from very simple movements
done in a laboratory with artificially manipulated feedback conditions.
From this research we have learned much about the types of feedback, but
other research on more real life activities has given much more insight on
how this feedback should be used. The second thing to consider is that all
the research points to the need for learners to rely on their own sensory
systems and own perception. An essential role of the instructor, thus, is to
promote the learner‘s awareness of perceptual information, provide an
environment in which problem solving and interpretation of sensory
information can take place, and overall give the performer opportunities to
modify and refine their own movements.
Discovery learning seems, and is, incompatible with common
instructional methods in which explicit techniques are rigidly modeled and
precise augmented feedback given. Golf and tennis swings are two such
examples. Gabriele Wulf, after finding consistent results showing that
focusing attention on precise movement techniques slowed learning and
reduced performance, questioned the use of teaching explicit techniques.
Teaching explicit techniques and biomechanical methods prevents
individuals from exploring and exploiting their individual psychological
and physiological abilities. Different individuals cannot perform the exact
same movement or accomplish the task in the same manner. Close
inspection of the top performers in rigidly constrained biomechanical
movements, like golf, reveals very different mechanics even if the overall
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movement seems similar. That is, they accomplish goals (lifting a weight,
shooting a basket, etc.) by different means.
The deliberate practice model provides a unified framework for practice
Ericsson and his colleagues over the past 15 years have done an
abundant amount of research documenting the acquisition of expert
performance. Using musicians primarily, but drawing upon research on
athletes and other professionals, these authors identified a number of key
factors that characterized how the experts practiced. The posited that
maximal performance, even elite performance, is not gained because of
innate abilities, nor is gained through more and more practice, but is a
result of what they termed deliberate practice. These authors suggested
that there is a direct or monotonic relationship between the time spent in
deliberate practice and improvement in performance. Since the original
framework was developed, other researchers have investigated its
applicability to both individual and team sports, and have made suitable
adjustments to the model that we include here.
The features of deliberate practice
Deliberate practice is characterized by six elements; (1) a task
designed to take into account previous knowledge of the performer, (2)
immediate feedback to the performer, (3) repetition of tasks or similar
tasks, (4) a specific intention to improve skill or overcome weaknesses, (5)
a strong motivation to improve, and (6) maximal effort.
Task Based on Learner Knowledge. Simply put, practice must be
designed for the individual based on their abilities and existing skill set.
These abilities may also include physiological or psychological
characteristics. The performer and the coach must be able to recognize
what this previous knowledge is and build upon it. This feature requires
the instructor, as in discovery learning, to get inside the learning situation
match the performer‘s abilities, needs, and wants, with the practice
environment.
This concept also applies to team sports, in which team practice is
designed around the attributes of the collective team abilities. Team sports
pose a challenge to practice, because individuals must not only improve
their individual skills, but must integrate these skills within the team.
Immediate feedback/knowledge of results. This feature seems
incompatible with discovery learning, but is not necessarily so. It does not
mean that the performer gets augmented FB from a coach on every trial.
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What is does mean is that the performer, with effort and intention,
continually analyzes they do in order to improve, which, of course,
requires feedback. For example, teams simply do not run through
offensive or defensive plays over and over again. They analyze what went
wrong and correct it the next time. Augmented FB from coaches is
sometimes descriptive or prescriptive, but the best feedback is designed to
encourage individuals and teams to figure out a solution on their own. In
this regard, augmented feedback is often in the form of a question, even
something as simple as, ―What are you going to do to avoid your opponent
next time‖?
Repetition of the task or similar tasks. Ericsson‘s data from
musicians revealed that practice was highly repetitive. This should not be
construed to mean that there was little or no variation. The nature of
instrument playing makes it look like the repetition is consistent, but
expert performers are constantly modifying their intentions, emotions, and
approach to playing. Data from sport research reveals that considerable
time is spent on the relevant tasks, including individual training, individual
practice, and team practice. The basic tenet of ―do it, do it again, keep
doing it until it is done right, and then do it more until it is better than
right,‖ still holds true.
Repetition of tasks is familiar to anyone attempting to learn a
motor skill, from riding a bike and driving a car to weaving a basket and
running hurdles. From our prior discussion of variable versus massed
practice, it would seem that pure repetition would not be consistent with
the idea that variable practice is better than massed practice. But repetition
is more complex than it first seems. Nikolai Bernstein, a Russian
neurophysiologist in the mid 1900s from whom many theories of motor
control have been derived, once commented that repetition is not repeating
the movement solution, but repeating the process of solving the movement
or finding a movement solution. Each movement, for example each stroke
of a tennis forehand drive off a ball machine, is a unique movement in that
it attempts to be a better movement than the one before it. This can only
happen effectively, of course, if the individual is intentionally attempting
to do so. Bernstein‘s research on blacksmiths found that these highly
skilled hammerers produced very precise patterns of hammer head
movement, but that the movements of the associated limbs and joints
varied a great deal. He observed that this was repetition without repeating,
and highlights that the nervous system is continually striving to modify
and adapt the large number of degrees of freedom to solve the movement
problem.
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Varying the movement context, such as adding contextual
interference, promotes complex problem solving and thus trains
information processing. Promoting information processing is a strength of
the discovery learning approach and enables a much better transfer of
motor performance from the practice setting to the game setting. This can
be done even when the movement is ―repeated‖ over and over again.
Specific intention to improve skill and/or overcome weaknesses in
performance. The previous deliberate practice tenets are only useful if
practice is intentional. The goal of practice is not simply the overarching
goal to get better, but each practice session must have some improvement
in some factor. Even if the course of learning results in a performance
decrement (remember plateaus and learning stages), there must be a
specific outcome and process goal to direct the course of practice and the
performer‘s mind set. Put differently, the intent of practice is not to play,
not to work hard, not to have fun, but all effort is focused toward
improvement. Of course, this intentionality drives attention.
Intention must be a combined effort of the instructor and learner,
and based on the learner‘s level of performance, skills and abilities, and
the identification of a pathway to expert performance. This pathway
necessarily includes the practice of activities that are the most challenging,
the most aversive, or that have the most room for improvement. Experts
continually strive to learn the next step or overcome the next obstacle
rather than continually practice what they already know. The expertise of a
coach in matching the individual to a practice roadmap is a hallmark of
successful coaching and cannot be underestimated.
In order to overcome weaknesses athletes need to engage in a
variety of activities to identify the weaknesses and overcome them. Helson
and his colleagues (1998), for example, noted that soccer players and field
hockey players engaged in individual training such as weight lifting and
video analysis, team practice, sport specific learning like journaling,
imaging, and coaching, and tailored everyday life activities around their
sport, like sleeping and studying.
A strong motivation by the individual to improve. Achieving a
high level of performance is a long hard road filled with setbacks. Teasing
out the smallest amount of improvement may take years and is thus not
very motivating. The highest level performers not only have a strong
motivation to succeed, but to improve and master performance.
A maximal effort given in practice. Without maximal effort
maximal improvement cannot be achieved. From previous chapters, we
know that effort is both a psychological and physiological process. Effort
must be maximal day in and day out, and year in and year out, with the
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caveat that rest it vital. Effort during practice is directed differently than
effort during work or play, based on intentionality. Effort during work is
designed to produce a quality product reliably, and often automaticity and
efficiency are desired. Therefore, exploring new methods of unknown
reliability are overlooked in favor of well-entrenched methods that
produce reliable results. Practice, however, should be intent and effortful
toward improvement and thus reliability becomes less of a concern.
The constraints of deliberate practice are difficult to overcome
The characteristics of deliberate practice have associated with them
constraints, making it difficult to actually engage is sufficient deliberate
practice. These constraints, as observed by Ericsson and his colleagues,
have come under some debate in recent years in regard to sport
performance. These constraints are (1) time, (2) resource availability, (3)
motivation, and (4) effort.
The Time Constraint. According to deliberate practice theory,
performers must engage in deliberate practice over at least 10 years to
achieve expert performance, and over this time the experts accumulate
more hours of purposeful practice than their less successful counterparts.
This does not mean that a 16 year old gymnast engaged in 4 hours of hardcore practice at age 6, but does mean that she engaged in some form of
gymnastics-relevant training at that age. Ericsson noted that the 10 year
rule applied to those who began as children, because during the maturing
years adaptation is more pronounced. Beginning an Olympic quest at age
20 does not fit the 10 year rule.
Cote and his colleagues have extensively studied Australian and
Canadian elite athletes and have determined that these athletes engage in
three phases of sport commitment over time; the sampling years (ages 512), the specializing years (ages 13-15), and the investment years (16+).
During the sampling years the children begin developing and refining a
variety of motor skills from various sports and games. The number of
sporting activities lessens during the specializing years as the athletes
begin to focus their time and effort toward specific activities. In the
investment years there is total commitment to the sport and expert
performance becomes a life focus. These authors have categorized the
nature of practice over the childhood development years as free play,
deliberate play, structured practice, and deliberate practice. Deliberate play
differs from deliberate practice in that the main outcome is fun rather than
improvement. Note, however, that structuring the play environment
requires the performer to take charge of their own practice environment to
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meet intentional goals, and provides a backdrop to begin improving skills
that ultimately increases participation enjoyment.
The time frame tenet appears to hold true for both individual
athletes and team athletes, though the nature of practice may differ.
According to Helson et al. (1998) elite level team sport athletes not only
spent more accumulated time in deliberate practice, but especially spent
more time in team practice as they became more experienced.
The Resource Constraint. Deliberate practice requires time, energy,
and the availability of resources such as coaches and facilities. It also
requires willing parents and often times, money. The resource constraint is
more obvious in activities like gymnastics and figure skating, and is less
obvious in sports like long distance running. In fact, elite distance runners
have often come from resource poor countries like Ethiopia and Kenya. In
these cases it is necessary to look at the resources that are available and
how they contribute to success. In the case of Ethiopian distance runners,
the abundant resources may be cultural support, time, difficult running
terrain, and opportunities to run. Money and winter training facilities are
less important.
The relative age effect highlights the resource constraint. It is well
recognized that in team sports, which are divided up by age groupings, that
the older children in the age grouping are more successful due primarily to
advanced physical development and emotional maturity. The children then
tend to be more successful at higher age groups as well, which according
to a number of researchers (Ericsson et al., 2009; Mujika et al., 2009) is
due to them receiving more resources. Because of their early success the
children are afforded more time, coaching, and encouragement by parents
and other influential persons.
The Motivation Constraint. Ericsson‘s data from musicians
indicated that motivation to practice and commit to a life of singular focus
was difficult, particularly because of a lack of rewards for practice and the
lack of enjoyment engaging in practice activities. Data from athletes (e.g.,
Helson et al., 1998) suggests that athletes tend to enjoy engaging in a
number of different practice activities, but motivation is still a problem for
many. Ericsson et al. (2009) commented that it is plausible that motivation
may be an inheritable characteristic; that enjoyment in domain specific
activities, a penchant for hard work, and even a desire to be the best may
have a genetic root.
The Effort Constraint. Because maximal effort – both physical and
mental – must be given in each practice session and over years, it is easy to
become fatigued and it is necessary to take time for recovery. Generally,
maximal effort cannot be given for more than 4 hours per day, and 2 hours
151
may be a more realistic time. Longer practices should be split up with
times for recovery, which is especially important for athletes. The amount
of time (per day and days/week) increases with adaptation to practice, but
does not necessarily includes activities related to practice, like watching
game films.
Genetics versus practice; can we resolve the nature versus nurture
question?
Stories abound of child prodigies attaining high level performance
in activities ranging from chess to music to sport. These stories suggest
that expert performance can be obtained without years of practice, and that
genetic qualities supersede practice. These stories, however, generally
overstate the actual achievements of children (remarkable for age, but not
expert compared to adult experts), and underestimate the amount of
practice the children have had even at a young age. Nevertheless, it is clear
that genetic qualities contribute to success. The genetic contributions to
performance are easy to infer in young children, but it does not mean that
these qualities are not obtainable, or even necessary, for expert
performance in later years. Ericsson and his colleagues, and many sport
science researchers like Baker and Cote, maintain that regardless of the
existence or non-existence of genetic qualities that it is practice and not
genetics that leads to expert performance. These authors note that genetic
qualities may lead to domain selection, but after that the precocious child
prodigy may simply get more attention and resources, and hence face
fewer constraints, thus allowing them to achieve a higher level of
performance.
There are others, of course, that maintain that genetics provide the
fundamental capabilities specific to certain sports and activities, and
without them expert performance is impossible to achieve. Muscle fiber
type, for example, is suggested to be important for more than simply
domain selection. We will not attempt to answer this question, but have
only provided a framework that regardless of genetic makeup, can enable
individuals to reach their highest potential.
Creating the Environment for Practice and Training
Knowing how to create a training environment based on dynamic
systems theory, discovery learning, and deliberate practice seems to be a
daunting task. Ives and Shelley (2003) laid out a four-step process to do so
they termed psychophysical training, specifically for the development of
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sport specific strength and power. The goal of psychophysical training is to
maximize the specificity of physiological adaptations to sport settings.
These guidelines focus on the functional training goal of bringing the
situational needs and constraints of real-life activities into the training
environment to enhance training effectiveness. Some researchers (Bobbert
& Van Soest, 1994; Voigt & Klausen, 1990) have reported that simply
improving strength may not lead to enhanced power or speed of complex
movements unless an athlete undergoes task-solving practice with their
newly enhanced muscle strength. Thus, the athlete must blend the trining
with the right environmental task constraints. This environment includes
many psychophysical elements that are specific to individual sports.
Altering movement intent and attention elements is a starting point for
manipulating the cognitive environment necessary for enhancing the
opportunity for sport-specific physiological adaptations to take place.
The four steps are:
1. Determine the physiological, perceptual, and psychomotor
factors and skills required for successful performance. This information
can come from the scientific literature as well as coaches and athletes
themselves. It may be necessary to draw upon data from similar sports if
that is the only data available. It is imperative that sport-specific
characteristics be identified, because the psychological skills for one sport,
or generic skills, may not work for another sport (Birrer & Morgan, 2010).
2. Determine the specific constraints that influence movement and
performance outcomes and the obstacles that need to be overcome for
learning to take place. Define these obstacles and constraints as problems
to be solved. This list should be specific to individual athletes based on
their unique abilities, strengths, and weaknesses.
3. Create a training environment that addresses strength or power
as well as the psychomotor and mental factors necessary for performance.
As a starting point, address mental effort, attention, and intention to
determine the mental factors necessary for training. Training need not
address all of these factors at once and can progress from simple to more
complex.
4. Carefully present constraints, obstacles, and cues in a fashion
that allows the athlete to discover on their own the best way to accomplish
goals. Monitor progress and present new constraints and obstacles when
learning plateaus.
A number of researchers have used similar guidelines with a high
level of success. For example, Hewett et al. (1996) reported remarkable
improvements in teenage girls' (volleyball players) jump height and power.
They also found changes in neural coordination that the authors' linked to
153
improvements in injury prevention mechanisms. These improvements
were far more than what is normally seen after a normal training program,
and can likely be attributed to the unique training method used. Their
plyometric training was more than just physiological effort. They used
structured jumping and landing practice, emphasized on technique, and
used verbal and visual cues.
Summary and Application
In this chapter the basic guidelines for organizing the practice
environment and ways to provide feedback to learners was presented. The
common feature of practice and of feedback was that it works best when it
promotes intentional problem solving by the learner. Mental practice, in
the form of imagery, was seen as an important component of practice
when done intentionally. Setting an intentional mind set was suggested to
be a component of mental practice leading to direct physiological
adaptations necessary for improved performance.
Three frameworks for practice were examined. Singer‘s 5-step
approach confirms previous discussions of the important of an external
focus of attention, intention, and imagery. Combining discovery learning
tenets with deliberate practice provides a strong theoretical and practical
framework for conducting practice based on focusing practice toward
individual needs while promoting individual exploration of movement
solutions. Movement solutions must be relevant to environmental, task,
and individual constraints as indicated by dynamical systems theory. The
role of the instructor in creating the most effective learning environment is
essential to this process, and is very difficult.
The ideas presented in this chapter, particularly discovery learning
and deliberate practice, are not new. Performers, coaches, and instructors
for centuries have used these principles, which have now been formalized
and streamlined based on research findings. These principles apply not
only to improving motor skill performance, but also in improving the
fundamental physiological abilities through training. The concepts of
feedback, intention, attention, effort and motivation, scheduling, and
competent instruction are just as applicable in the training setting.
By using deliberate practice strategies, coupled with an
understanding of the critical role that neuromuscular control principles
play in strength, power, speed, and in the training of specific sport skills,
coaches and conditioning specialists can enhance athletic performance by
more effective training in the weight room and on the field.
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UNIT 3
MIND, BODY, AND
BRAIN
Up to this point we have looked at the psychological and physiological
aspects of controlling movements. We have seen evidence of mind and
body interaction, but only on a limited basis for 'real' movements. In this
section the physiological and psychological are integrated together and
the full psychophysiological ramifications of training mind and body is
examined. We will then look at how movements performed in real world
circumstances are produced. We will discuss muscle tone and posture —
important in their own right and basic properties of almost all other
movements. Then we will look at training methods.
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CHAPTER 10
THE NEUROPHYSIOLOGY OF
LEARNING AND TRAINING
Chapter Outline
I. Central Nervous System Adaptations to Learning
II. Exercise Neuroscience
III. Summary and Application
f the mind and body are truly connected then there should be
direct evidence on how they influence one another. In this
chapter we look at this evidence, first through learning effects on the brain
and then exercise effects on the brain.
I
Central Nervous System Adaptations to Learning
In a previous chapter it was emphasized repeatedly that one‘s
mindset during practice and training influences the physiological
adaptations that arose from the training. In this chapter we will look at the
changes to nervous system that also accompany practice and training, or in
other words, the neurophysiological changes that reflect learning.
CNS changes reflects efficiency and resource adaptation
It has been demonstrated by magnetic resonance imaging (MRI),
electroencephalography (EEG), cerebral blood flow (CBF), and other
imaging techniques that as a task is learned various areas of the brain
become more and some areas become less active. Brain activity is revealed
by changes in blood flow, metabolism, and electrical activity. Generally,
after weeks of motor skill practice, less brain area is active during
performance of the task. It is thought that this reflects some level of
automaticity and freeing up of resources as the brain becomes more
efficient in task execution. It has also been found in some cases that more
brain areas are active after learning, which is thought to reflect use of
previously unused resources in order to maximize movement capability.
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In some cases it is not more or less brain area, but different brain areas that
are used. It is speculated that how the movement is organized or planned
appears to changed – even using different brain areas – but the nature of
this change is speculative.
Heavy strength training may increase the amount of "neural drive"
to the muscles, in part due to increased descending commands (from
supraspinal centers) and increased motor neuron excitability or reduced
presynaptic inhibition in the spinal cord (Aagaard et al., 1998). Overall, is
it believed that as learning takes place the brain adapts to devote the
necessary resources to produce movements that are more efficient, more
capable, and more functional to the environment.
Morphological changes are many
Along with changes in resource use, there is good evidence for
changes in neuronal structure. More synaptic connections, more
neurotransmitter receptor sites, and more efficient neurotransmitter
receptor sites are formed and the most efficient neural pathways are found
and used to a greater extent than other pathways.
These changes reveal that the brain is quite plastic. It can change
its morphological structure (e.g., new synapses), and even the somatotopic
map of motor and sensory areas (the Brodmann areas and perhaps the
homonculus) can be altered (Carroll et al., 2001; Classen et al., 1998;
Jancke et al., 2000; Karni et al., 1998; Petersen et al., 1998; Smith et al.,
1999.)
Similar changes appear in the spinal cord. In general, it looks as if
more synaptic connections can be made and certain neuronal pathways can
be facilitated. The motor neurons themselves may become more excitable.
These changes appear to be important in the development of enhanced
motor drive related to strength and power development.
Adaptation to the neurochemical systems
The brain communicates with the body via two pathways. The first
is the direct neuronal transmission system in which signals are passed back
and forth through neurons. The second system, sometimes called the
parallel neurochemical system, uses neurochemicals (hormones,
neurotransmitters) to relay information. This transmission of information
may happen within the brain itself or between brain and body. Some
neurochemicals are released directly by neurons whereas others are
released by glands and organs after being signaled by the nervous system.
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Neurons can directly secrete chemicals to a wide-ranging area though
terminations with blood vessels, thus releasing substances into the blood
(e.g., neurohormones). Alternately, some neuron release chemicals just to
the interstitial space surrounding the neuron (e.g., paracrines).
Some neurochemicals have specific and direct synaptic targets, like
other neurons, and are thus precise in their influence. Other
neuorchemicals float around in blood or other fluids until they bind to
appropriate receptors on specific cells that may be widely distributed
throughout the body. These neurochemicals have widely varying actions
on the target cells. They may serve as on-off switches, increase enzyme
production, promote growth and protein synthesis, change the diffusion
properties of the membrane, alter metabolism, change secretory and
electrochemical properties, and likely other influences that have yet to be
discovered.
How the parallel communication system works on a grand,
integrated scale is complex and not fully understood, and so some
speculation is in order. We can speculate strongly that what happens in
the brain is chemically transmitted to the body. For example, during
stressful conditions the brain secretes certain neurochemicals that bind to
receptors in particular areas of the brain, giving rise to emotions like
anxiety. Moreover, the same type of brain receptors are found in the
intestines, giving rise to ―gut feelings.‖ In another example, the same brain
receptors found to bind to neurochemicals associated with depression and
similar emotions are also found on immune system cells. These
neurochemicals may bind on immune cells and decrease the cells'
functional ability.
Even less in known about the adaptations this systems undergoes,
but it is speculated that the amount and types of neurochemicals, and the
affinity of receptors to these chemicals, changes according to practice and
training. Evidence to this effect can be best found in the study of behaviors
on the immune system and health, a field of study known as
psychoneuroimmunology (PNI). Chronic stress or depression may cause
a relatively long-term depression of immune function through the receptorneurochemical connection. The evidence of stress-related disease
reinforces this association.
But what about motor behavior? Much less in known on this topic
than PNI, but sometimes emotions are said to be stored in the body. More
specifically, storage of negative emotions in the muscles is termed
muscular guarding or emotional armor. It is well known that the peripheral
biochemical system adapts a great deal to exercise or lack thereof. For
example, to get more glucose into the muscle cell during exercise, more
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glucose carriers are put into the muscle cell membrane to aid glucose
transport into the cell. Insulin promotes this increase in glucose carriers
after the insulin binds to insulin receptors on the cell membrane. Chronic
adaptations to aerobic exercise include an increase in the number of
insulin receptors and an increase in the affinity of these receptors to
insulin, making the cells more responsive to circulating insulin.
The essential issue here is that psychological state, including
emotions, intent, effort, cognitive processing, influence how and what
physiological adaptations occur. It also means that getting out of a bad
motor habit or performance staleness (e.g., a plateau in weight lifting)
takes considerable effort and intent and constant attention to avoid
backsliding.
Detraining and delearning are not the opposite of training and learning
The neurophysiological changes that occur as a result of learning
are not necessarily reversed in conditions of detraining and delearning.
Muscles and tissues undergo atrophy and well understood metabolic
changes, but detraining changes in the nervous system are not as well
understood. Animal model studies suggest that chemical adaptations and
dendritic sprouting due to training are lost after detraining, but these
studies simply have not been conducted on humans. Studies on humans are
equivocal on the loss or preservation of neural drive due to detraining
caused by immobilization of a limb.
Detraining and delearning in humans is generally the result of
injury or disease. A simple view is that neurological adaptations and motor
performance that occur during these times is simply deteriorates back to its
pre-trained state or even further. However, the ―original‖ state cannot be
obtained because of knowledge and experience that does not go away. The
body must also make adaptations to the deteriorated condition. For
example, if the muscles are weakened then the body might need to adapt
entirely different coordination patterns to accommodate the weak muscles.
This is a common phenomenon in injury or disease; people acquire
entirely different movement patterns such as posture and gait to
compensate for dysfunctional systems. Consider also that psychosocial
factors quickly and dramatically influence motor behavior. Anxiety,
tentative actions, and so forth result in modified movements. Researchers
have classified some persons rehabilitating from injury as copers, adaptors,
and non-copers, identifying their level of functional mobility. It is
unknown at this point what physiological or psychological factors may
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contribute to the recovery and subsequent classification from coper to noncoper.
Getting back to top form may require entirely new approaches,
even to the extent of unlearning compensatory movements. There are no
easy answers but the remarkable capabilities and plasticity of the
neurological and musculoskeletal systems will certainly allow
considerable changes to take place.
Exercise Neuroscience
Exercise neuroscience is the study of the influence that physical
exercise has on brain neurophysiology and brain function. Most research
in this area has examined the role of exercise on mood state and cognitive
function (exercise psychology), neurophysiological modifications in the
brain resultant from fitness training, and central nervous system fatigue.
Exercise likely has a positive influence on mood state
Exercise – primarily aerobic exercise – is often recommended as a
mental health wellness strategy. An abundant amount of research supports
this recommendation, with evidence that mood can be enhanced, anxiety
reduced, self-efficacy and positive affect improved, self-esteem improved,
mild depressive symptoms reduced, and possibly a reduction in
physiological reactivity to psychological stressors. These exercise effects
can be experienced from an acute exercise bout or following chronic
exercise. However, despite what seems to be a compelling amount of
research and anecdotal evidence, these findings are not universal nor are
they without problems. Much of the data are beset by methodological
issues, like expectation effects, gender-related changes, issues regarding
the exercise environment, and publication bias. For example, researcher
Thomas Plante has shown that many people feel better before exercise,
suggesting expectancy effects and not some exercise-induced
psychophysiological adaptations.
Researchers have yet to uncover if mood state alterations are
rooted in biological adaptations. It is known that the parallel
neurochemical system is highly active during exercise, for example,
hormones contribute to amino acid (neurotransmitters such as tryptophan
and serotonin) formation and uptake in the brain, which is hypothesized to
modulate pain and CNS fatigue, but the data are unconvincing.
Endogenous opioids and monoamines (e.g., endorphins, dopamine, and
serotonin) can be released and have pain-reducing and mood altering
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effects, but their exact role is unknown. At this point the best explanation
for the effects of exercise on mood is a complex biopsychosocial model,
that is, that a confluence of physiological processes, and social and
psychological issues contribute to mood state and mental health outcomes.
Exercise may influence cognitive function in elders
Exercise is also recommended as a cognitive health strategy. A
large number of individual reports showing improvement in cognitive
function, memory, and learning, or delayed loss in executive function, in
fit or exercising elders supports this view. Meta-analyses, though, show a
weaker association between exercise and elderly cognitive function.
Despite what is commonly reported in the popular press, the effect of
exercise on slowing dementia is unknown, and there is a scarcity of data
regarding the role of exercise in influencing cognitive function in young
and middle-aged adults. The limited data on these populations suggests
that acute exercise may improve short term cognitive performance,
perhaps by maintaining goal orientation.
Regardless of the uncertainty over cognitive outcomes due to
exercise, there are clear and demonstrable neurobiological effects in elders
who exercise, or are fit, or who maintain motor skill proficiency.
According to a review by Cottman et al. (2007), human and animal models
suggest many brain-related changes, including cell proliferation, increased
blood flow, alterations in brain chemistry, neurotransmitters, receptors,
synapses, capillarization, an overall slowing of brain tissue loss, and
changes in brain activation areas have all been reported. Even with these
data it is difficult to come to strong conclusions about the role of exercise
and cognition function in elders. Outcome data is supported by brain
imaging data, but there are psychosocial and self-selection interactions that
come into play.
A model of neurological protective mechanisms arising from exercise. Cotman et al.,
TINS, 30:464-472, 2007)
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Exercise as a cognitive enhancer for children has little support, but is
widely practiced
Exercise has long been promoted to improve academic
performance in school children, and indeed most data suggest a positive
relationship between physical activity and academic performance. The
evidence, though, is generally weak, short term only, and without a strong
causal link. For example, is the exercise effect a neurobiological cause, or
is it self-efficacy, or is it psychosocial, or some aspect of concentration? It
is difficult to tease out these influences, in part because the sociocultural
and socioeconomic interactions are large. The effect of exercise on
learning disabilities like ADHD and dyslexia is highly controversial, and is
without a great deal of supporting data.
Central fatigue accompanies muscular fatigue
Fatigue is defined as an inability to produce the required or
expected force or work, though the behavioral expression of fatigue often
does not correlate with the physiological indices. It is well known that
faltering muscle physiological and biochemical mechanisms are associated
with fatigue. Along with depletion of ATP and other energy substrates, the
accumulation of lactate and other metabolic byproducts impair action
potential propagation and cellular function. Researchers have shown that
muscular fatigue is not the only site of fatigue, but that the central and
peripheral nervous system may also falter. For example, there is
speculation that excessive work leading to muscle weakness or fatigue
may disrupt performance (e.g., balance performance) because of
alterations to proprioceptive mechanisms (Johnston et al., 1998). There is
strong evidence that fatiguing exercise (e.g., triathalon) reduces reflex
sensitivity (e.g., stretch reflex is difficult to elicit and is weak). This could
be due to disfacilitation (removal of facilitation from muscle spindles
afferents) or presynaptic inhibition of the reflex circuitry (Avela et al.,
1999). It could be that free nerve endings in the muscle (group II and IV -mostly chemoreceptors and nocioceptors) respond to a buildup of
metabolic wastes. These free nerve endings have powerful effects on
inhibitory interneurons connecting to motor neurons in the spinal cord.
Experiments have shown that electrical stimulation given to
fatigued muscles during maximal voluntary contractions elicit a stronger
contraction than the voluntary effort alone, strongly suggest that the CNS
has an involvement in fatigue. Other experiments have shown that
unilateral fatiguing exercise results in fatigue on the contralateral limb,
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further supporting the idea of central fatigue. It is speculated that fatiguing
conditions lead to a loss in central drive, perhaps from lowered oxygen
levels. It has been hypothesized that non-motor areas in the brain begin
integrating signals differently which may alter sensations and behavioral
states, and some evidence points to disruptions in neurochemical systems,
including serotonin, acetylcholine, and dopamine. How these changes
contribute to behavioral alterations, and how the behavioral alterations
contribute to neurological changes, remain to be seen.
Summary and Application
Movement training, either through practice or exercise, has a real
and measureable effect on the central nervous system. Morphological
changes, neurochemical changes, and topographical changes highlight the
considerable plasticity exhibited in the human brain that comes about from
both generalized exercise training and specific practice. Though the
neurophysiological changes are measureable, changes in cognitive
function and mood are harder to pinpoint, in part due to many confounding
factors.
The application of this information is that exercise and practice
must be thought of as nervous system training as much as body training.
Psychophysiological outcomes are specific to the practice and training
variables, and thus practice and training should be directed toward the
desired outcomes.
Bibliography and Other Sources
Classen, J., Liepert, J., Wise, S., Hallett, M., & Cohen, L. (1998).
Rapid plasticity of human cortical movement representation induced by
practice. Journal Of Neurophysiology, 79(2), 1117-1123.
Jäncke, L., Shah, N., & Peters, M. (2000). Cortical activations in
primary and secondary motor areas for complex bimanual movements in
professional pianists. Brain Research. Cognitive Brain Research, 10(1-2),
177-183.
Karni, A., Meyer, G., Rey-Hipolito, C., Jezzard, P., Adams, M.,
Turner, R., & Ungerleider, L. (1998). The acquisition of skilled motor
performance: fast and slow experience-driven changes in primary motor
cortex. Proceedings of the National Academy of Sciences, 95(3), 861-868.
Petersen, S., van Mier, H., Fiez, J., & Raichle, M. (1998). The
effects of practice on the functional anatomy of task performance.
Proceedings of the National Academy of Sciences, 95(3), 853-860.
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Smith, M., McEvoy, L., & Gevins, A. (1999). Neurophysiological
indices of strategy development and skill acquisition. Brain Research.
Cognitive Brain Research, 7(3), 389-404.
Cotman et al. A model of neurological protective mechanisms
arising from exercise. TINS, 30:464-472, 2007
Herrington L, & Fowler E. (2006). A systematic literature review
to investigate if we identify those patients who can cope with anterior
cruciate ligament deficiency. Knee, 13(4):260-265.
Pert, CB, Dreher, HE, & Ruff, MR. The psychosomatic network:
foundations of mind-body medicine. Alternative Therapies in Health and
Medicine, 4(4), 30-41, 1998)
Aagaard et al., J. Sports Sci., 16:400-401, 1998)
Avela et al., 1999
Carroll et al., Exer. Sport Sci. Rev., 29:54-59, 2001;
Johnston et al., 1998
Pert, C. Molecules of Emotion, (1997)
Thomas Plante
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CHAPTER 11
MUSCLE TONE, POSTURE, AND
BALANCE
Chapter Outline
I. Muscle tone
II. Posture and Balance
III. Measuring Posture and Balance
IV. Posture, Balance, Core, and Low Back Pain
V. Summary and Applications
uscle tone and postural control are the foundation from
which all goal-directed movements are produced. They are
not generally considered motor skills themselves, but rather, are
components of motor skills. Stability (i.e., balance) and biomechanical
alignment (i.e., posture) are outcomes of tone and postural control. The
importance of training these components have reached the popular fitness
and sport settings, but with little understanding and little scientific backing
for training rationale. Core training, for example, is an application of
posture training that has exploded in its popularity but in our estimation
generally lacks a thorough basis. In this chapter we look at balance as
being an outcome of postural control, and muscle tone being a primary
mechanism to control posture.
M
Muscle Tone
The definition of muscle tone is much simpler than implied by
fitness training centers that advertise ―toning and sculpting.‖ Muscle tone
refers simply to the force with which the muscle resists lengthening, that
is, its stiffness. High tone means the muscle is stiff and resistant to stretch;
low tone means the muscle is compliant and stretches easily. High and low
stiffness are both desirable at times, and therefore the idea that ―toning‖
the muscle is desirable has little meaning for healthy persons.
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Tone is a function of elastic elements and neural activation
Muscle tone is dependent on two factors, (1) the viscoelasticity of
the muscle and tendon elastic elements and (2) the level of neural
activation of the contractile elements. Muscles with rigid connective tissue
and muscles with contracted muscle tissue have more tone than muscles
without rigid tissues and muscles in a relaxed state. For example, a
chronic baseline level of neural excitability, which often coincides with a
sensitive muscle spindle, creates more tone by slightly contracting the
muscle tissue which in turn tugs on the elastic elements. In deep relaxation
the majority of the tone is provided by the inherent properties of the
passive elastic elements because the muscle tissue is compliant.
Pathological conditions reveal how these two elements contribute
to tone. Excessive muscle tone, called hypertonia or rigidity, is often a
result of spasticity. In spasticity and related pathologic conditions,
hypertonia is a result of uncontrolled muscle contractions that keep the
muscle in a stiffened state. Removal of supraspinal inhibition of reflexes
causes the reflexes to go uncontrolled, thus resulting in hypertonia. The
site of the CNS dysfunction will impact where the hypertonia appears.
Some transient pathological conditions, like cramping, lead to increased
muscle activation through dysfunction to the muscle membrane or
peripheral neurons.
Hypotonia is a pathologic condition of too low a level of muscle
tone, and is generally a result of too little muscle activation. Hypotonia is a
symptom of conditions like upper motor neuron disease, which causes low
neural activation even at rest, and the inability to fire the muscles to stiffen
them. This makes ―background‖ postural actions and trunk stabilization,
like sitting up, difficult.
Other conditions, albeit not necessarily pathological, influence
tone. Circulating reproductive hormones in women during menstrual
phases and pregnancy increase the elasticity of muscle and connective
tissue, thus reducing tone. Increased temperature increases muscle
elasticity, muscle damage from exercise or sickness may increase tone and
result in pain.
Measuring tone is subjective
The ―right‖ amount of tone is vague and transient and hard to
measure. The right amount of tone is that which enables effective and
skilled posture and movement, although poorly constructed movements do
not automatically imply faulty tone. Conversely, it is foreseeable that
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improvement in tone and posture may improve upon even skilled
movements. For these reasons tone is a muscle quality commonly
measured despite the inherent measurement difficulties.
Muscle tone in healthy persons is often measured by the amount of
passive ROM of the joint and muscle length tests, but these measures are
also dependent on many other factors like joint health. A better measure of
tone is by using a force gauge to measure how much force it takes to move
a limb through its ROM, though this measure is also problematic due to
the influence of other joint factors.
In clinical settings, for example pediatric physical therapy,
hypertonicity and hypotonicity are often determined by palpation of the
muscle tissue, muscle weakness, and observation of rigidity in the muscle
in addition to assessing passive ROM. Poor muscle tone is often diagnosed
when basic movement patterns, like sitting upright, are difficult. Palpation
and observation of muscle tissue form and bulk are sometimes used to
evaluate tone in healthy persons, particularly in comparing symmetry of
muscle groups. Muscles that are flattened or sagging compared to their
contralateral counterparts are sometimes suggested to be hypotonic due to
inhibition, and muscles appearing tight and bulky are said to be
hypertonic. The reliability and validity of these subjective measures have
not been thoroughly investigated.
Muscle tone has three primary functions
Muscle tone is regulated for three main purposes (1) to maintain
―background‖ posture and joint stability, (2) to regulate the storage and
release of elastic energy, and (3) to regulate force dampening. In
maintaining posture
and joint stability,
stiffness of the relevant
muscles are kept at a
specific level to resist
lengthening, thus
limiting the sway
amount or joint
movement. Tone is set
at a level to maintain a
background level of
posture and stability,
that is, a baseline level
necessary for function.
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For example, along the length of the spine, the small paraspinal muscles
like the intertransversus and interspinalis muscles are stiffened to increase
vertebral joint stability and strategically relaxed to enable movement.
As we saw in previous chapters, the muscle elastic elements store
energy and then release it. This is especially true in walking and running
and makes movement more efficient. Altering tone is one way to regulate
the amount of energy stored and released. For example, during running the
gastrocnemious is stiffened to better and faster transmit force from the
muscles to the ground and take advantage of the stretch-shorten cycle. The
diagram below shows a landing sequence with low gastrocnemius tone
(left figures) and the high gastrocnemius tone (rightmost figures). A
compliant muscle on the left results in an inability to stop ankle
dorsiflextion, thus the heel crashes down and transmits high forces
throughout the skeletal system. The rightmost figures have high stiffness,
preventing the heel from hitting the ground.
Coinciding with the
regulation of energy storage
and release, the elastic
elements help dampen rough
movements to smooth them
out and make them less
jerky. Altering tone stiffens
or slackens the elastic
elements, thus regulating the
amount of dampening.
Compliant Tone
Stiff Tone
Controlling the level of tone
begins reflexively
The neural system actively controls the amount of tone. At a low
level contraction the muscle begins tugging on the elastic elements,
thereby creating a stiffer muscle. Most of this neural control is done
automatically by the muscle spindles in a typical reflex feedback manner.
If the muscle is stretched too far because of low tone, the spindle is
excited, which activates the homonymous muscle, which increases the
stiffness of the muscle to counteract the stretch.
The gain in the spindle feedback system refers to how strong a
stretch is needed to elicit a contraction. A high gain, also known as high
sensitivity, means that a small stretch will cause a large contraction. A
low gain means a large stretch will result in a small contraction. This gain
can be adjusted in several ways, it is sufficient to understand that the gain
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can be controlled automatically by spinal and supraspinal centers and
consciously from supraspinal centers.
Tone is influenced by behavioral state and chronic adaptations
Albeit controversial, there is some evidence to suggest that acute
and chronic behaviors influence tone, generally leading to excessive
tonicity and associated postural changes. In particular, fear responses and
startle behaviors cause reflex potentiation and stereotypical movement
behaviors, such as a cowering posture. Repeated trauma (physical and
psychological), fear, and associated stressors may result in conditioned and
chronic muscular actions, generally in the form of high tone (stiff muscles)
and further resulting in maladapted postures, like
tightened shoulders and a lowered head and
Several movement re-education
neck. For example, it can be speculated that
methods, for example the
years of repeated harassment and ridicule in
Feldenkrais Method and the
Alexander Technique, are
young girls who are highly sexually developed
purported to address movement
for their age may lead them to minimize their
dysfunction arising from muscular
guarding. Proponents of these
development with forward shoulders, forward
methods maintain that by engaging
in patterned and self-aware
head, and an overall scrunching in of the body. It
movements that emotional stress
is possible that this ―hiding‖ type of response
carried in the muscles can be
released, thereby freeing up mind
moves from an emotional response to being a
and body. Countless anecdotes
permanent fixture. A cowering posture, or
support this idea, but solid
experimental and clinical evidence
aspects of it, is probably not uncommon to
is lacking.
others who have spent periods of time in fear of
physical or mental abuse. Consider also the
startle response. When startled or frightened, the shoulders move up and
the head and neck retract. A large amount of neck and shoulder stiffness is
created, which conceivably might lead to a chronic tension in people who
are frequency subject to startle and fear. The important point to remember
is that supraspinal centers use all of the information at their disposal to
help regulate tone.
An expanded view on the psychophysiology of tone comes from
examining the effects of emotion on gait. Biomechanical and observational
studies have shown that emotional state (e.g., depression) is so reflected in
gait that gait biomechanics can be used as a psychotherapy diagnostic tool
(e.g., Sloman et al., 1987). Gait differences in genders, cultures, settings
reveal that gait is a very strong body language. Attempts to capture the
emotion in motion range from biomechanical studies to dance evaluation
using Labanonotation. Labononotion is a measurement tool to evaluate
dance through what he termed body, effort, shape, and space. This
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evaluation addressed the mechanics of
movement as well as the emotion and
other underlying psychological aspects
contributing to the expression of the
dance.
Posture and Balance
Posture is most commonly understood or defined as the way we
stand, and indeed, the most common posture measurements evaluate the
biomechanical alignment of standing. Alignment is a component of
posture, but posture is much more than that. Posture is broadly defined as
the carriage and orientation of our body parts to
one another (e.g., biomechanical alignment)
Turning a double play is a study in postural
and the body to the environment at any given
control and controlled disequilibrium The
shortstop‘s trunk must be stabilized to enable a
point in time. The purpose of postural control
hard throw to first base, all while constrained
is to maintain both alignment and spatial
to touch second base and avoid being taken out
by the runner. The body must also be stabilized
orientation, in other words, to orient the body
to enable the legs to avoid the runner, but ready
in a stable position to enable effective
for an anticipated impact from the runner.
movement. Stability may be whole body
stability to prevent falling, body part stability
to enable other body parts a firm foundation to
move, or joint stability. The amount of knee
varus or valgus, for example, is a measure of
knee posture. Whole body postural stability is
one function, or one outcome, of postural
control, and is more commonly referred to as
balance. Balance is typically defined as the
ability to maintain the center of mass (COM)
within the base of support (BOS). Another
definition is that balance is the ability to
maintain the body in equilibrium and controlled disequilibrium.
Postural control means more than standing still; it is maintaining a
stable position that is ready for diverse actions while walking or running or
falling. For example, good postural control will allow one to maintain a
stable position even while reaching out and grasping something
unexpectedly. Good postural control enables effective limb movements
during off-balance situations, such as a targeted grasp of a hand railing
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while falling. All of these situations fall under the heading of posture, and
all are outcomes of postural control mechanisms.
Posture relies on tone to support purposeful movement
The relationship between tone and posture and
purposeful movement is shown in the illustration
(Wiesendanger, 1997). Person 1, standing on the
shoulders of person 2, represents purposeful movement.
Person 2 represents posture, and he is supported by
person 3, who is tone. Purposeful movement will fail if
either posture or tone is insufficient. Postural orientation
can vary widely, but it cannot do so without tone
―pushing‖ with the right magnitude and timing.
Many different systems contribute to postural control
Postural control actions are dependent on or
influenced by many different systems. At the most basic
level postural control involves reflexes. Postural
reactions are triggered by sensory inputs from the muscle, vestibular
system, and visual system. Constantly ongoing is subcortical regulation of
tone initiated by reflexive action and abrupt reflexive postural corrections,
both of which aim to keep the body‘s center of mass in line with the
support base using continual feedback and correction. Postural movements
also result from ocular (visual) inputs, but normally in an open loop
fashion. Visual systems, as we learned in an earlier chapter, provide
information to anticipate and prepare for upcoming events; in postural
control this is one aspect of what is termed anticipatory postural control
(more on anticipatory postural control below). Auditory feedback also
allows anticipatory control, but not to the same extent as vision. All
sensory inputs are integrated in the CNS and weighted to provide the CNS
with the most relevant data regarding ongoing balance and orientation
requirements. For instance, under conditions of poor vision, or challenging
vestibular conditions, the CNS may rely more on proprioceptive inputs.
Postural control also relies on inherent neuromuscular systems and
synergies, like CPGs and coordinative structures. Musculoskeletal
components and function influence postural control, like elastic element
stiffness, muscle strength, and muscle and joint health. Biomechanical
constraints, both internal and external, impose limits on the control
systems. Finally, postural control, particularly anticipatory control, is
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influenced by psychological and perceptual mechanisms based on
experiences, attention demands, emotional state, and intention.
These systems – reflexive, sensory integration, neuromuscular,
musculoskeletal, biomechanical, and psychological all contribute to three
levels of postural control; (1) reflexive, (2) autonomic, and (3) voluntary.
Standing body sway and righting reflexes are two notable examples of
reflex mechanisms working in the background to maintain balance. Even
during ―quiet‖ standing the body sways back and forth and side to side. As
the body sways forward (due to gravity) the dorsal muscles, primarily the
triceps surae, stretch. This stretch activates the muscle spindles, causing a
stretch reflex contraction to stiffen the dorsal muscles and bring the body
back into correct vertical alignment. Gravity then pulls the body forward
again, and the process is repeated for every moment of standing. Spindle
sensitivity is set to regulate the amount of sway and the vigorousness of
the corrective response. Vestibular and neck reflexes work in conjunction
with the muscle spindles at a subtle background level, and also at an more
abrupt level during postural instability, such as an arm thrust designed for
landing impact.
Reflexive, autonomic, and voluntary systems combine for postural
strategies
Regardless if the postural reflex is initiated with a functional
stretch reflex, or vestibular, or visual input, the
postural mechanisms generally begin at the point in
In our labs we‘ve seen some
contact with the support surface (e.g., ankle). Then,
students unable to break from
using a stepping strategy even
through a series of sequenced, coordinated, and
under the smallest of perturbations.
minimized stretch reflex activations the body is
This is a learned response, similar
to our observations that dancers
balanced. If this does not work to balance the body,
and gymnasts struggle to not use a
hip strategy during large
such as when standing on slippery ice, then another
perturbations. Why?
strategy is adopted. For example, reflex activations
may start at the knee or hip instead of the ankle.
Whole body adjustments to maintain balance generally begin at the
ankle. This ankle strategy provides the quickest way to maintain balance
under normal circumstances. If the ankle strategy is not sufficient to
maintain balance, the hip strategy may be used. The hip strategy enables a
larger amount of correction. In more extreme balance challenges a
stepping strategy is employed. Another strategy, the suspensory
strategy, involves going into a crouching flexed behavior to lower the
center of mass. This is most often done by those afraid to fall or those in
an entirely unfamiliar environment. The elderly and very young are more
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likely to use this strategy. Although there seems to be a natural progression
from one strategy to another, many physiological, biomechanical,
psychological, or experiential factors can influence which strategy is
employed. Ankle problems, for example, will lead one to use an
alternative strategy.
Automatic and conscious control of posture is highly task specific
Working on top of postural reflexive actions are automatic
subconscious postural systems and fully conscious voluntary actions.
Automatic postural systems are a combination of both learned behaviors
and modified reflexive actions that work as coordinative structures and
synergistic movements. Automatic postural movements are generally
specific to specific movements or specific perturbations, and occur without
awareness or conscious initiation. For example, a loud warning of an
incoming projectile, like ―Heads up!‖ results in different postural
movements in people with different experiences. In most individuals this
warning results in controlled startle response, with head down and arms up
to protect the head. The body tightens up. Experienced individuals may
respond with an abrupt arm protective action while maintaining an upright
head to look for the projectile.
Voluntary postural control is conscious control over postural
systems to maintain stability, and is most often displayed in anticipation of
an upcoming perturbation. Consider, for example, a novice exerciser
playing catch with a heavy medicine ball. The first time the ball is caught
the person may be knocked over due to the unanticipated force of the ball.
After this unpleasant introduction the novice begins to voluntarily stiffen
the trunk and legs, and take on a crouched and stable athletic posture in
preparation to catch the ball. After considerable practice the catching
posture becomes less stiff, more efficient, and automatic. The exerciser no
longer needs to think about postural stiffening as this becomes a
component of the catching action.
Threat and uncertainty may increase voluntary control
It is beneficial that postural control is largely reflexive and
automatic, for this frees up cognitive and motor resources. During postural
threats and uncertain environmental conditions, however, voluntary
postural control often takes over. Numerous research reports have shown
that with activities of increasing balance challenge (e.g., a swaying
platform or changing visual references) that reaction time slows, which
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indicates that cognitive resources like attention are going to postural
control (Redfern and Jennings, 1998). Others (e.g., Benjuya and Melzer,
1998) have shown that a demanding cognitive task can reduce standing
posture steadiness, which may be more prominent in the elderly (Rankin et
al., 2000). Reflex gain is often reduced under conditions of poor vision
and unstable surfaces (Hoffman and Koceja, 1995). In particular, with no
vision the reflex gain is reduced (less reflexive strength, less chance to be
activated). The same was true for the unstable surfaces. Some of these
results may be due to changes in afferent input from visual and cutaneous
receptors, but it could also be supraspinal in origin. Similar results have
been found for walking on a balance beam – the amount of reflex gain is
reduced when on the beam compared to walking on a treadmill (Llewellyn
et al., 1990). What these studies show is that with increasing complexity
(no vision, unstable surfaces, balance beam) individuals tend to not rely on
the automatic processes, but rather, take over control of the postural
balance more voluntarily and thus reduce reflex influences.
Postural control is reactionary and anticipatory
Postural control actions are designed to react to disturbances as
well as prepare for anticipated disturbances. Reflexive and automatic
postural actions predominate reactionary control, whereas automatic and
voluntary predominate anticipatory control. Supraspinal control over
postural reflexes is also a part of anticipatory control.
Anticipatory postural control comes
in two basic forms. The first is based on
upcoming or expected environmental
circumstances or bodily actions. These
postural adjustments are based largely on
visual inputs and previous knowledge. For
example, prior to stepping on ice the trunk
may stiffen. The second form is referred to
as anticipatory postural adjustments or
APAs. APAs are postural movements that
accompany all or most all movements. They
are designed to stabilize joints and body
parts or the whole body prior to the
execution of the motor skill. They are, in
fact, a component of the motor skill. The
figure on the right illustrates how APAs
work. The subject in the figure pulls on the
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lever (biceps b. contraction) in reaction to an auditory stimulus. Reaction
time of the elbow flexion is about 200 ms. Before the biceps b. contracts is
an APA contraction of the gastrocnemius; at a reaction speed (125 ms) that
is faster than voluntary reaction time. The gastrocnemius contracts to
stabilize the body to counteract the pulling force of the elbow flexion. This
experiment reveals that the motor plan has two parts, the first is a postural
stabilization and the second is the goal-directed movement. The APA may
be an innate mechanism, but it is modifiable to environmental and task
conditions, and individual characteristics.
APAs are necessary components of even the most fundamental
motor skills. During running, for example, leg stiffness is adjusted by the
runner to meet the needs of different ground surfaces, even before the leg
strikes the new surface. It has been shown that vertical movement of a
runner‘s center of mass and head does not vary from a hard surface to a
soft surface, indicating that postural stiffness is automatically adjusted to
the ground softness (Ferris, Liang, Farley, 1999). Among the most
dramatic illustrations of anticipatory postural control is during falling or
landing from a jump. While in flight and prior to ground contact, the
impact-absorbing limbs (legs or arms) contract to stiffen the muscles in
order to prepare for impact forces. The precise coordination of this preactivation, such as the muscles involved and the timing and strength of
contraction, is highly dependent on the task itself and is a preprogrammed
phenomenon (Avela et al., 1996). In other words, the pre-activation
landing sequence is sent down from the CNS and appears to work with
and be modified by inputs from visual, vestibular, and proprioceptive
sensory systems. Moreover, this whole coordination mechanism appears
to be alterable through practice.
Note that anticipatory postural adjustments can be turned off by the
CNS in cases of high postural instability. This is probably because the
APAs might actually destabilize the body is such cases, so they are
reduced (Aruin et al., 1998). Proximal and distal muscles have different
roles during APAs; proximal and trunk muscles seem to be more patterned
and active with normal and expected movements, distal and limb muscle
APAs may be more active during more unusual postural disruptions
(Shiratori & Latash, 2000).
According to Leonard (1998), APAs accompanying voluntary
movement have four characteristics; (1) they can be either reactionary or
anticipatory in order to minimize body displacement during the voluntary
movements, (2) they are adaptable to conditions and contexts of
movement, (3) they are influenced by an individual's intent and emotional
state, and (4) they are modifiable through learning and experience. The
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role of intention in postural adjustments was demonstrated in an elegant
experiment by Earl and Frank (1992). These authors showed that leg and
trunk postural control changed when subjects had to lift a tray with wine
glasses versus tumblers. The fragile and unstable wine glasses required
more precision, which modified the postural control. These authors also
showed that postural control changed if the task was self-paced versus a
timed pace.
Measuring Posture and Balance
Research based evaluation of postural control typically employs
EMG to evaluate muscle activation patterns of postural support muscles
during goal directed movements or during perturbed movements. In
addition, sophisticated measures of sway (e.g., sway velocity and
magnitude) and balance using force platforms or stabilometers are
common research tools used to infer postural control mechanisms. Clinical
evaluation of postural control is most often measured by evaluating static
posture (standing or seated), sway, and various aspects of balance.
The ideal posture is elusive
The ―ideal‖ standing static posture is shown at right. Theoretically,
with all the joints in alignment there is less stress through the
musculoskeletal system, and therefore, less chance of
developing chronic musculoskeletal pain and a decreased risk
of injury. Despite the intuitive rationale of this suggestion,
there is little evidence to support the idea that small or
moderate deviations from postural alignment cause movement
dysfunction and pain. Clearly some postural deviations are a
result of pain, injury, disease, emotional guarding, or habitual
mis-use, but the extent to which postural deviations cause
pain, injury, emotional affect, or movement dysfunction has
proven difficult to quantify. Part of the difficulty in classifying
―good‖ posture or ‖poor‖ posture is that some musculoskeletal
systems are simply not able to be in alignment and individuals
live perfectly well with mis-alignment. Indeed, many athlete
groups, such as gymnasts, wrestlers, and soccer players have
been found to have poorer static alignment than non-athletes.
The cause and effect relationship between posture and
performance is unknown. Similarly, there exists some data
showing a correlation between poor back and shoulder posture
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and injuries, but causal and effect factors and co-founding variables have
not been identified.
Balance measures emphasize sway and stability
Balance is an outcome of postural control, and for this reason
balance is used to infer postural control mechanisms. Balance measures
vary widely in their nature and sophistication, ranging from simple timing
of single leg standing to center of pressure measures on tilting
computerized force platforms (also called stabilometers). Sway
characteristics, including direction, magnitude, and velocity, are among the
most common measures of balance
and stability. Sway is objectively
Functional limitation tests include the Romberg test and the
functional reach test, and test batteries like the Performance
measured on computerized platforms
Oriented Mobility Test and the Berg Balance Scale.
and also by visual observation. Large
Strategy tests include the Clinical Test for Sensory
and jerky amounts of sway are
Integration and Balance (CTSIB) and tests that evaluate
ankle, hip, and balance strategies.
considered to reflect poor postural
control. Though standards and norms
have been established for some
balance measures (generally by
equipment manufacturers) and some
balance measures have been
associated with injury and
impairments, interpreting many
balance tests for otherwise healthy
individuals are often ambiguous. For
example, large sway magnitudes have
been positively correlated with an
increased risk of falls, yet some
training program like Tai Chi have
Tests for underlying impairments that may influence postural
control the most. Lower extremity muscle strength, ankle
been shown to increase sway
ROM, Somatosensation and other sensory tests
magnitude while decreasing fall risk.
Balance tests are best used to
identify problems, and the potential source of the problem or implication
of the problem. To do so, balance tests are designed to test for (1)
functional capabilities or functional limitations, (2) motor or sensory
strategies, and (3) underlying sensory or motor or cognitive impairments.
These tests are best suited in cases of dysfunction, for example examining
sway characteristics following a concussion, or comparing single leg
stability of a non-injured leg to an injured leg.
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Posture, Balance, and Core Training
Over the past 10 years there has grown a greater appreciation of the
role of postural control in supporting and maintaining efficient movement.
This has been followed by a host of exercise programs aimed at improving
posture, balance, and core strength. Many of these programs are directly
aimed at overcoming musculoskeletal problems like low back pain that
purportedly stem from postural control dysfunction.
Core training may be effective in reducing musculoskeletal problems
Muscles of the ―core‖ specifically refer to the intrinsic
musculoskeletal system of the trunk, but in practical usage must include
the musculoskeletal system that attaches the trunk to the extremities and
function more to stabilize and orient rather than move limbs. Trunk
flexors, extensors, rotators, and lateral flexors (abdominal muscles, erector
spinae, small paraspinal muscles, quadratus lumborum) are considered the
main core muscles, but hip movers like the small rotators, illiacus and
psoas, gluteals, and scapular stabilizers may also be considered core
muscles. Core training, thus, aims to improve strength, endurance, and
control of the core muscles. In practice this includes a variety of
callisthenic type exercises, balance exercises
Core training has two purposes, to (1) stabilize the spine and pelvis
to prevent low back injury and pain, and (2) to provide a stable center base
from which limb movements and associated motor skills can be effectively
carried out. Core training almost always includes trunk flexion, extension
and rotation movements, but only recently have isometric exercises, like
lateral planks, become popular. Research from Stuart McGill and his
colleagues at the University of Waterloo have identified a series of
exercises useful to stabilize the spine and prevent low back injury. These
exercises include a strong measure of isometric actions with the purpose to
build endurance and neuromuscular control more so than strength.
Exercise training has an uncertain effect on athletic performance or
postural alignment
Although one purpose of core training is to create a stable trunk in
order to improve motor skill execution, there is little evidence in athletes
and relatively healthy persons that core training actually improves
performance. This lack of data, however, should not necessarily be
interpreted that core and balance exercises do not work. Rather it reflects a
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lack of data in general and difficulty in determining the contribution of
abilities into specific motor skill performance.
For literally hundreds of years exercise has been prescribed to fix
misaligned posture, including severe abnormalities like scoliosis. Because
posture abnormalities may be associated with muscle tightness and
weakness and asymmetries, it is plausible that exercise training, in the
form of stretching, calisthenics, and resistance training, may be an
effective treatment. On the whole, however, there is little evidence
showing demonstrable effects of exercise on posture. Even exercise
programs touted to improve posture and carriage, like Pilates-based
exercise, have only been shown to be minimally effective at best.
Limited evidence does show some improvement in scoliosis when
treated early in children, and there are scattered reports of specific postural
improvements, such as hip and shoulder symmetry, following exercise
interventions in injured persons or those with dysfunction. Exercise in
these situations may aid in restoring postural alignment back to pre-injury
levels.
Balance training is best when task specific
Generic balance exercises, such as wobble board exercises and
movements on highly cushioned mats, have been shown to improve
various laboratory measures of balance, and have been shown to improve
some functional performance like walking speed in impaired individuals.
Balance exercises have even been shown to improve reflex responses to
perturbations in elderly subjects. Generic balance exercise may improve
some aspects of motor performance in otherwise healthy persons, for
example single leg balance training may improve leg strength, but
specifically focused balance training can have a much larger impact on
skills and abilities like vertical jump height, hopping stability, strength,
and injury prevention. Taube and colleagues‘ review of balance training
noted that balance training for postural stability has direct consequences to
sensory systems, motor systems, and the CNS sensorimotor integration.
The best balance training methods are task specific, which
coincides with data showing that balance is not a general motor ability. For
example, gymnasts have been shown to have better balance than other
athletes, but only under conditions of reduced vision, implying a trainingrelated adaption.
Effective balance training for injury prevention illustrates that task
specificity is a psychophysical issue. Early work from Hewitt and his
colleagues showed that jump training emphasizing biomechanically
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correct landing (stable landings) within a game specific attentional focus
environment was critical in the success of their program.
Summary and Applications
Postural control is controlled by three systems working in unison
with one another. The ―lowest‖ level is purely reflexive – largely by
muscle spindles – that controls sway, joint (e.g., spinal column) stability,
and overall muscle tone. The second level is autonomic. Autonomic
control is based on both innate (e.g., CPGs, coordinative structures) and
learned behaviors that become automatic responses to movement or in
preparation for movement. The final level is purely voluntary. These are
willful postural adjustments to maintain stability, generally in anticipation
of an upcoming postural threat.
Two outcomes of postural control are biomechanical alignment
(―posture‘) and balance. Identifying very poor posture is relatively easy,
but uncovering the causes of poor posture and prescribing effective
training solutions is difficult, and may not exist. Balance problems are also
easy to identify, and with proper balance testing the underlying postural
control dysfunction may be identified and rehabilitated.
Posture training may only be useful in extreme cases, but balance
training can have dramatic and far reaching influences on motor behavior.
Generic balance training may have some effect on clinical populations, but
task specific balance training can have large effects on both clinical and
healthy – even athletic – populations.
Bibliography and Other Sources
Taube W, Gruber M, Gollhofer A, Spinal and supraspinal
adaptations associated with balance training and their functional relevance.
Acta Physiologica 2008 Jun; Vol. 193 (2), pp. 101-16
Hawes MC, The use of exercises in the treatment of scoliosis: an
evidence-based critical review of the literature. Pediatric Rehabilitation,
2003 6 (3-4), pp. 171-82;
Hrysomallis C, Goodman C, A review of resistance exercise and
posture realignment. Journal Of Strength And Conditioning Research,
2001 15 (3), pp. 385-90
Kuo YL, Tully EA, Galea M,P Sagittal spinal posture after Pilatesbased exercise in healthy older adults. Spine, 2009, 34 (10), pp. 1046-51
Rankin, J., Woollacott, M., Shumway-Cook, A., & Brown, L.
(2000). Cognitive influence on postural stability: a neuromuscular analysis
184
in young and older adults. The Journals Of Gerontology. Series A,
Biological Sciences And Medical Sciences, 55(3), M112-M119.
Hoffman, M., & Koceja, D. (1995). The effects of vision and task
complexity on Hoffmann reflex gain. Brain Research, 700(1-2), 303-307.
Shiratori, T., & Latash, M. (2000). The roles of proximal and distal
muscles in anticipatory postural adjustments under asymmetrical
perturbations and during standing on rollerskates. Clinical
Neurophysiology, 111(4), 613-623.
Sloman et al., 1987
Wiesendanger, 1997
Redfern and Jennings, 1998).
Benjuya and Melzer, 1998)
Llewellyn et al., 1990
Ferris, Liang, Farley, 1999
Avela et al., 1996
Aruin et al., EEG Clin. Neurophysiol., 109:350-359, 1998
Leonard (1998),
Earl and Frank (1992
185
CHAPTER 12
ORTHOPEDIC INJURY,
REHABILITATION, AND
PREHABILITATION
Chapter Outline
I. Orthopedic Injury
II. Controlling Joint Stability
III. Orthopedic Rehabilitation and Prehabilitation
IV. Summary and Application
n the previous chapter balance training was seen to be an
effective intervention for a number of movement dysfunctions.
In this chapter we will look at common orthopedic injuries – namely joint
injuries – and their effects on the neuromuscular system.
I
Orthopedic Injury
Injuries to the bones, joints, and muscular system result in damage
that extends beyond the main tissues. Joint injuries, in particular, typically
involve damage to the identifiable tissue (e.g,. meniscus, ligament), but to
surrounding tissues and sensory and motor systems. Furthermore, surgical
interventions also cause damage.
In a typical joint injury, the knee for example, the ligaments may
be the primary injured tissue, but it likely that cartilage, the joint capsule,
tendons, bursae, tendon sheaths, the surrounding skin, and other tissue in
the area may be damaged. Each of these tissues has a specific function to
maintain joint function, from providing mechanical stabilization to
producing nutrients or lubrication. Nearly all tissues in the joint are likely
to have at least one type of sensory ending, and often three to four different
receptor types. These receptors may participate directly in reflex arcs, act
as modifiers to muscle spindle activity, help maintain and monitor tissue
homeostasis like inflammation, provide pain signals, and provide feedback
to the CNS regarding joint integrity and joint action. The abundance and
variety of receptors in some tissues marks these tissues as highly important
186
―stimulus receivers,, and underscores the role that sensory detection plays
in maintaining joint stability.
Joint stability is compromised by more than mechanical damage
Following a joint injury the stability of the joint may be
compromised for several reasons. The most obvious is a reduction in
mechanical stability due to weakened and damaged tissues. The second
reason is that damage to the tissue alters the mechanical properties of the
tissue, thereby changing the nature of the stimulus-response characteristics
of the receptors within the tissue and the nature of the information sent to
the CNS. Receptors may respond differently to changes in force, velocity,
or acceleration, or may not longer be directionally tuned after tissue
damage. Joint stabilizing reflexes may no longer work satisfactorily. The
third reason is that this change in proprioception and other sensory
signaling after injury must be re-interpreted by the CNS in regards to joint
movement, joint health, and joint stability. That is, the brain must re-learn
the meaning of the altered sensory signaling, and if it does not, joint
stability may remain compromised. For example, arthrogenic muscle
inhibition may continue long after injury, weakening the surrounding joint
musculature. The last reason is that sensory ending and neurons
themselves may be damaged, leading to a loss in sensory function.
Data from Hogervorst & Brand, JBJS, 80-A:1365, 1998
187
Controlling Joint Stability
The diagram below illustrates that joint stability is much more
involved than reliance on musculotendinous and ligamentious mechanical
support. At rest these are important systems, but during dynamic actions
joint stability relies on postural control mechanisms, both reactionary and
anticipatory.
Reflex responses acting to stiffen muscles surrounding joints are a
well-recognized phenomenon. Receptors in the anterior cruciate ligament,
for example, have a direct reflex arc to activate the hamstrings
musculature, helping to pull the tibia back into place following anterior
displacement forces. Shoulder capsule sensory systems appear to have
similar functions in maintaining glenohumeral positioning and stiffness.
Despite the actions of these reflexes, which in some cases can be less than
50 ms in latency, they are typically too weak or too slow to maintain
stability against large perturbations. A growing body of evidence points to
feedforward and
anticipatory postural
control to maintain and
ready the joint for large
disturbances. Preactivation
of knee and ankle
musculature, for example,
not only controls
dampening and force
transmission, but braces
the joints against
destabilizing forces.
Furthermore, in highly
trained individuals,
feedforward and
anticipatory control not only prepares the joints for expected stresses, but
also for unexpected stresses and perturbations. Movement training to
prepare for the unexpected, as described below, is the key element in
successful injury prevention programs.
The influence of joint receptors often extends far beyond the
homonymous joint. Consider that the function of knee ligament receptors
is often more to excite gamma motoneurons of the muscle spindles than to
directly excite the alpha motoneurons of the skeletal muscle. That is,
ligament receptors may act more to modulate the muscle spindle stretch
reflex than directly activate skeletal muscle. Regardless, these receptors
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are active not only when the joint goes to its limit, but during normal range
of motion. When the ACL or other ligament is damaged, the sensory
signals often result in aberrant reflexes or poor kinesthesia. Furthermore,
distal joints and muscles can be affected, for example, ankle problems
have been shown to affect gluteal muscle action and hip motion. Or, reflex
response times can be lengthened. Generic pain can also affect muscle
activation. For example, low back pain may alter the subconscious and
automatic activation of gluteal muscles during gait. In all of these cases
the poor motor control can be considered to be a result of inappropriate
sensory functioning or inappropriate perception combined with adaptive
voluntary motor control strategies. Mechanical insufficiency by the
supporting connective and muscle tissue can most likely be overcome by
traditional rehabilitation training, but it is just a part of the overall
mechanisms that control the joint's stability. The nervous system,
including perception, must be trained.
Orthopedic Rehabilitation and Prehabilitation
Traditional rehabilitation following joint or musculoskeletal injury
focuses on tissue healing followed by range of motion and strength
exercises, then followed by functional task specific activities. However,
despite gains in strength and normal clinical findings, individuals may
continue to have joint instability and fatigue – often appearing during
performance. A large amount of data is emerging to indicate that
improvements can be made to this approach.
Newer models of musculoskeletal rehabilitation often begin the
rehabilitation process sooner, stressing tissues even as they are healing.
Typical strength and range of motion exercises are still necessary, but
there is an earlier start to adding functional activities to the strength and
range of motion exercises, for example, beginning sooner with closed
chain exercises.
The most notable changes in rehabilitation programs, and the key
features of prehabilitation programs, are the move away from typical
calisthenics, running, cutting, and jumping exercises designed stress the
injured musculoskeletal system in task-specific ways. Instead,
rehabilitation and prehabilitation focus on training better movement
quality. Many of the same exercises are used in the new models, but the
intention of the exerciser is different. The goal is to produce high quality
movements within a task-specific framework, that is, to train coordination
for injury prevention. These movement training programs have been
labeled sensorimotor training, neuromuscular training, balance training,
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jumping and landing training, and the misleading ―proprioceptive‖
training. Because these programs specifically target joint stability via
better movement quality and improved postural control, we believe the
most descriptive term is simply joint stability training, which is consistent
with strength training and aerobic training in describing the intended
outcome of the training program.
Hewitt et al. (2006) summarized several key features of effective
programs for knee and ankle injury prevention based on an extensive meta
analysis of the literature. All programs – successful and non-successful –
involve various forms of jumping, leaping, or hopping, generally in the
form of plyometric training. Most programs incorporated running and
cutting, and some use strength training. The successful programs all
emphasized movement quality and postural control over fitness
development, and teaching movement quality was the foremost
responsibility of instructors. The successful programs had similarities in
how movement quality was taught. The first was the use of critical
analysis of movement technique and the use of feedback by instructors.
Sport specific injury prevention strategies, such as landing techniques,
were identified. Second, athletes were encouraged to use imagery
alongside instructor verbal and visual cues in order to formulate movement
solutions, rather than simply follow prescriptions. Third, athletes were
encouraged to evaluate movements, for example using video, and devise
their own prevention strategies.
The programs shown to be effective follow deliberate practice and
exploratory learning strategies. They are designed to overcome weaknesses
(poor biomechanics and poor movement patterns), and movements are
repeated in different contexts to solidify the basic movement patterns and
to make them adaptable to changing environments. Though instructors
have identified where the athlete needs to be (e.g., reducing valgus knee
motion), it is up to the athlete to figure out the best way to reach that goal.
From what we have learned in previous chapters, this type of training
targets the psychophysiological systems as much as musculoskeletal
systems.
Proper exercise may influence sensory system repair
Joint and postural stability training aims to improve sensory and
motor integration and overall coordination mechanisms, but this raises the
question of what happens when the sensory system is absent, such as in the
case of tendon or ligament grafting. In ligament reconstruction surgery the
damaged ligament is removed and replaced by the person‘s own tissue, but
190
no nervous system tissue is replaced. In an ACL reconstruction the new
tissue is stapled to the bone and is left to heal. There may be sensory
endings in the tissue, but no innervation by sensory neurons means that the
tissue cannot serve as a proprioceptive device. Recent evidence, however,
shows that these tissues may reinnervate and provide sensory signaling
after months of healing. For example Tsuda et al. (2003) showed that these
grafts can (but not always) regenerate new mechanoreceptor afferent
pathway and reflex arcs. It is thought that existing mechanoreceptors may
grow new afferent neurons, and it is unknown if new receptors can also be
grown. Why some persons had regenerated, or strongly restored, sensory
pathways and others did not is not clear, but there is some evidence that
the level of regeneration was tied to the amount or quality of rehabilitation
exercises.
Whereas reinnervation may occur in cases of injury repair, there is
a paucity of evidence of other sensory morphological changes as a result of
training. For example, there is no evidence of intrafusal fibers
hypertrophy, but there is some animal evidence of intrafusal fiber
metabolic changes. Chronic changes in reflex behavior may happen,
perhaps by more synaptic connections in the spinal cord or by more
supraspinal enhancement of the reflex response. Long term morphological
adaptations to GTO pathways are not known. What is clearly the case in
altering sensorimotor behavior is that perception and resultant automatic
and non-automatic voluntary response to the perception is changed.
Summary and Application
Musculoskeletal injuries are common in activities of daily living
and athletics. Among the most serious of these injuries are traumatic
injuries to the joints involving cartilage or ligaments. These types of
injuries result in degradation of tissue mechanical performance and
dysfunction to sensory and motor systems responsible for maintaining
tissue integrity and joint function. Rehabilitation programs aimed at
restoring function and prehabilitation programs aimed at preventing injury
must focus on restoring/maintaining tissue integrity and sensory and motor
functional performance.
Joint and posture stability programs must focus on regional
neuromuscular function and overall body motor behavior such as
improved biomechanical movement control. This type of training, best
called joint and postural stability training, should be a necessary addition
to traditional physiological training designed to enhance physiological
capabilities like strength, range of motion, and aerobic capacity. Joint and
191
postural stability training is done to prevent injury and generally prepare
the body for the stresses of competition or life. When directly done to
prevent injury or prepare for occupational stresses, it is termed work
hardening.
Bibliography and Other Sources
Hewett TE, Ford KR, Myer GD. (????). Anterior cruciate ligament
injuries in female athletes: Part 2, a meta-analysis of neuromuscular
interventions aimed at injury prevention., The American Journal of Sports
Medicine, 34 (3), 490-498.
Myers JB, Lephart SM. (2002). Sensorimotor deficits contributing
to glenohumeral instability. Clinical Orthopaedics and Related Research,
400, 98-104
Caraffa, A., Cerulli, G., Projetti, M., Aisa, G., & Rizzo, A. (1996).
Prevention of anterior cruciate ligament injuries in soccer. A prospective
controlled study of proprioceptive training. Knee Surgery, Sports
Traumatology, Arthroscopy, 4(1), 19-21.
Hewett, T., Lindenfeld, T., Riccobene, J., & Noyes, F. (1999). The
effect of neuromuscular training on the incidence of knee injury in female
athletes. A prospective study. American Journal of Sports Medicine,
27(6), 699-706.
Tsuda, E., Ishibashi, Y., Okamura, Y., & Toh, S. (2003).
Restoration of anterior cruciate ligament-hamstring reflex arc after anterior
cruciate ligament reconstruction. Knee Surgery, Sports Traumatology,
Arthroscopy, 11(2), 63-67.
Hogervorst & Brand, JBJS, 80-A:1365, 1998
192
CHAPTER 13
STRENGTH, POWER, SPEED, AND
AGILITY
Chapter Outline
I. Strength and Power
II. Psychophysical Mechanisms of Strength and Power Production
III. Functional Strength and Power and the Rise of Psychophysical
Training
IV. Speed and Agility
V. Determining Strength, Power, Speed, and Agility Components
VI. Summary and Application
Strength and Power
A
rguably the most well recognized attributes of athletes in
most sports is strength and power. Feats of strength and
power, from throwing projectiles to wrestling opponents to
jumping and lifting weights, are ubiquitous across nearly every sport,
including sports once considered aerobic in nature. Strength and power
training are so recognized as essential to the development of athletic
performance that numerous lay and scholarly journals are devoted to this
type of training.
The fundamental tenets of strength training have been around since
before the early Greeks, but considerable debate still rages about training
variables. The purpose of this chapter is not to lay out these variables, but
rather, to focus on what is known about strength and power training and
how these variables can be applied in a psychophysical training regimen.
Strength and power come in many varieties
Strength is defined as the maximum force or torque one can exert
under specific task constraints. That means that strength can be determined
by a one-repetition (1-RM) max bench press, a maximal voluntary
isometric (MVIC) squat lift, a knee extension on an isokinetic
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dynamometer, or the weight of rocks one can lift. The task constraints may
include movement speed (e.g., fast versus isometric), movement type (e.g.,
concentric versus eccentric; isoinertial versus isokinetic), postures, and
muscle involvement, and so forth. Power as used in the context of strength
training and conditioning is defined as the rate in which strength or force
is exerted, or force x velocity. Maximum power is the point at which the
force exerted multiplied by the speed of movement is maximal.
Numerous subcategories of strength and power have been
identified. Among these are high speed strength, low speed strength,
reaction strength, explosive strength, and skill strength. High speed
strength is maximal force production using relatively light loads (e.g., <
30% of max strength) done at maximal velocity, high load strength is
maximal force developed using high loads at maximal concentric velocity.
High speed strength and low speed strength could alternately be labeled
high speed power and low speed power. The figure below illustrates the
relationships among low speed, high speed, and peak power areas on the
force-velocity curve. Reaction strength is capability of the neuromuscular
system to withstand stretch-shorten cycle contractions, that is, contractions
with a high eccentric load and a rapid eccentric to concentric reversal.
Explosive strength is measured by the
fastest rate of force development (RFD) of a
max: 100%
contraction, or the amount of time it takes to
low speed strength
reach a specific level of force. Skill strength
Strength
involves functional performance measures
peak power
of skills and abilities that are task specific.
30%
high speed strength
For example, box lifting for material
0
handling evaluation and two step approach
0
with a vertical jump for volleyball players
max:100%
Shortening Velocity
are skill strength measures.
Strength and power are defined in
different ways because tasks require different variations of strength and
power, and strength and power are not necessarily generalizable across the
strength and power spectrum. Though there is some measure of transfer,
strength and power performance and strength and power training are
largely specific.
Psychophysiological Mechanisms of Strength and Power Production
The mechanisms of force production are well known and are
described in basic kinesiology and exercise physiology textbooks. Briefly,
force and power production are dependent on muscle mass, muscle
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morphology (motor unit type), stretch-shorten cycle and other elastic
element factors, biomechanical and anthropometric characteristics, and the
neural control of motor unit behavior, including intramuscular and
intermuscular coordination. The most important of these factors, the neural
factors, are also highly modifiable in producing different forms or
expressions of strength and power.
The fundamental characteristics of training are also well known,
including overload and specificity. Training with very high loads to induce
motor unit firing changes has been termed neural training, training with
lower loads but large number of repetitions to induce fatigue and muscle
growth is called hypertrophy training, and training at the midpoint of the
force velocity curve has been termed peak power training and sometimes
ballistic training.
Identifying the contributions of these factors to the expression of
force production has largely come from controlled laboratory experiments,
few of which bear resemblance to the use of muscle force in activities of
daily living or sporting activity. The use of strength and power tests, for
example, hold little predictive value in categorizing high level athletes, nor
do they associate well with other abilities like speed and agility.
Among the confounding issues with strength and power tests are
psychological and skill-related factors. Cognitive strategies, generally in
the form of ―psyching up‖ or focused attention contribute to greater
strength production, at least in novice and intermediate level exercisers.
MRI evidence indicates that psyching up strategies may increase CNS
arousal and activation, which in turn may facilitate neural motor
commands. Among the most challenging factors to address in the
assessment and training of strength and power are skill related factors.
Even the most simplified strength testing protocol requires technical skill
to perform, and learning the technique may increase force output
dramatically. It is these skill-related factors that make the transition from
laboratory measures of strength to real world expressions of strength the
most difficult, and have given rise to functional strength and power tests.
Speed and Agility
In combination with strength and power, speed and agility are
considered essential components of athletic success. Speed is defined as
linear velocity and is measured by sprint times, typically 100m, 40m, or
10m. Agility is defined as the capability to stop and start and change
directions, and typically implies the ability to move laterally in a nonstandard gait, such as slide steps or carioca. Agility is measured by running
195
tests involving rapid cuts and changes in direction. Quickness is a term
that is often used to describe either speed or agility, but is more related to
agility. Quickness refers to acceleration or how fast speed can be
developed, particularly from a stationary start. Straight line acceleration is
inferred from 0-5m or 0-10m sprint times, or by taking split times in
sprints. Quickness in cutting maneuvers or in accelerating from a direction
change is the same as agility.
Agility and acceleration are often reactionary
Speed, acceleration, and agility rely on numerous physiological
abilities, such as muscle fiber type and body size. However, factors once
thought to be predictive of speed and agility, such as strength and power,
are now in question. The capability of strength tests like isokinetic knee
extension tests and squat tests to predict speed and agility performance is
highly influenced by methodological and individual factors such as test
familiarity, making such predictions difficult at best. Evidence of low
correlations between speed and agility also reveal the independent nature
of these abilities.
Perhaps even more challenging in determining speed and agility
factors are the differences between laboratory and actual performance
environments. As much as any underlying factor contributing to sports
performance, agility and straight line quickness are open skills dependent
on environmental circumstances. The rapid changes in direction or speed
are nearly always prompted from an external stimulus, and therefore have
a reaction time component. Not only is the speed of the agility movement
dependent on reaction time, but the quality of the movement is dependent
on the decision making during the reaction period. Recent research
comparing closed skill agility tests and open skill agility tests have
confirmed that the decision making component of agility is separate from
the movement component, and is a more important predictor of high level
performance.
Determining Strength, Power, Speed, and Agility Components
Understanding an individual‘s needs in order to maximize training
and practice is essential to the deliberate practice model, and training for
strength, power, speed, and agility are among the most difficult skills and
abilities to fit within the deliberate practice model. According to Newton
and Dugan (2002) the key biomechanic features of the movements must be
identified, either through direct testing, discussions with experts, or
196
scientific literature searches. Contraction type, range of motion, and speed
of movement are just a few of the movement characteristics that need to be
clarified. Analysis of high level performers may reveal certain qualities
these athletes‘ possess and provide starting points for training.
Ives and Shelley (2003) maintained that the perceptual challenges
of the sport or specific task needs to be examined, including reaction time,
decision making, environmental stability, and other psychological
constraints. Like the biomechanical, environmental, and task specific
constraints, these constraints must be introduced into the training
environment.
Functional Performance and the Emergence of Psychophysical
Training
A football lineman exploding from a crouched position is a
precisely crafted motor skill taking into account a multitude of
environmental, task, and individual specific constraints. Footing, timing,
characteristics of the opponent, game circumstances, tendencies of
teammates, fatigue, injuries, and desire are just a few of the factors that
play a role in the formation of the explosive motor commands. The typical
laboratory measure of explosive strength is sufficient in determining basic
muscle capabilities, but not necessarily the use of those capabilities on the
field. The need for more specific tests has given rise to functional strength,
power tests, and agility tests, and subsequently, functional training
programs.
Functional strength and power training has been used for centuries,
in fact, is seems that isolation of strength from the environment and the
reduction of strength down to its constituent components is a relatively
new phenomenon. The reemergence of functional strength and power tests
begin in rehabilitation, spread to occupational and sports settings, and is
just now beginning to make its way into wellness settings. Functional tests
are characterized by constraining the test to important aspects of real world
performance. Strength tests used in occupational settings, for example,
may require boxes be lifted and placed on shelves rather than
straightforward arm and leg strength tests.
Psychophysical training adds decision making and attention demands
Recently, functional tests and training have begun to add
psychological constraints to further mimic real world applications. These
psychological constraints mostly center on decision making and focus of
197
attention, both of which are driven by intention. For example, vertical
jumps while reaching for a basketball creates a rebounding intention and
focus of attention. Jump training up against a wall mimics the physical
barrier of a volleyball net and forces movement adaptations. Moreover, the
wall is an attention-demanding obstacle that distracts from the primary
objective and creates injury threats.
Designing and implementing psychophysical training programs
was described in an earlier chapter. Ives and Shelley (2003) laid out the
framework for identifying the psychological and perceptual constraints
within sport related tasks, and inserting these constraints into effective
strength and power training programs. Psychophysical training is not a
replacement for training aimed squarely at physiological adaptations, nor
should it be considered motor skill training, but rather, a bridge between
the two.
Summary and Application
Strength, power, speed, and agility are seen as critical components
to athletic success, yet the nature and extent of their association to success
has been difficult to quantify. Furthermore, the routine use of strength and
speed based training programs has not always been shown effective in
improvement in athletic performance. We believe a major issue in transfer
of abilities gained in the weight room to the playing field is the lack of true
functional training methods, that is, training methods incorporating
psychophysical aspects.
Psychophysical training brings the perceptual aspects of the task
and the environment into the training program, such that physiological
systems are stressed both psychologically and physiologically.
Knowledgeable trainers and coaches are able to bring the appropriate task
and environmental constraints into the training environment in order to
maximize transfer.
Bibliography
Aasa U, Jaric S, Barnekow-Bergkvist M, Johansson H. Muscle
strength assessment from functional performance tests: role of body size.
Journal Of Strength And Conditioning Research, 2003, 17 (4), pp. 664-70
Abernethy L, Bleakle C. Strategies to prevent injury in adolescent
sport: a systematic review. British Journal of Sports Medicine, 2007; 41
(10), pp. 627-38
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Abernethy P, Wilson G, Logan P. Strength and power assessment.
Issues, controversies and challenges. Sports Medicine, 1995; 19 (6), pp.
401-17
Gabriel DA, Kamen G, Frost G. Neural adaptations to resistive
exercise: mechanisms and recommendations for training practices. Sports
Medicine, 36 (2), pp. 133-49, 2006.
Ives JC, Shelley GA. Psychophysics in functional strength and
power training: review and implementation framework. Journal Of
Strength And Conditioning Research, 2003 17 (1), pp. 177-86
Ives, JC and BA Keller. Functional training for health. In: JK
Silver & C Morin (Eds.), Understanding Fitness. How Exercise Fuels
Health and Fights Disease. Westport, CT: Praeger Publishers, 2008.
Jaric S. Role of body size in the relation between muscle strength
and movement performance. Exercise And Sport Sciences Reviews, 2003
31 (1), pp. 8-12
Marcovic G. Poor relationship between strength and power
qualities and agility performance. The Journal of Sports Medicine and
Physical Fitness, 47 (3), pp. 276-83
McGuigan MR, Ghiagiarelli J, Tod D, Maximal strength and
cortisol responses to psyching-up during the squat exercise. Journal of
Sports Sciences, 2005 23 (7), pp. 687-92
Nedeljkovic A, Mirkov DM, Bozic P, Jaric S. Tests of muscle
power output: the role of body size. International Journal of Sports
Medicine 2009; 30 (2), pp. 100-6
Nedeljkovic A, Mirkov DM, Markovic S, Jaric S. Tests of muscle
power output assess rapid movement performance when normalized for
body size. Journal of Strength And Conditioning Research, 2009 23 (5),
pp. 1593-605.
Newton, RU, Dugan, E. Application of the strength diagnosis.
Strength & Conditioning Journal, 24(5): 50-59, 2002.
Sheppard JM, Young WB, Doyle TL, Sheppard TA, Newton RU.
An evaluation of a new test of reactive agility and its relationship to sprint
speed and change of direction speed. Journal of Science And Medicine in
Sport 2006 9 (4), pp. 342-9
Tod D, Iredale F, Gill N. 'Psyching-up' and muscular force
production. Sports Medicine, 2003; 33 (1), pp. 47-58
199
CHAPTER 14
PSYCHOPHYSICAL TRAINING FOR
FUNCTIONAL HEALTH
(Chapter adapted from Ives, JC and BA Keller. Functional training for health. In: JK Silver & C
Morin (Eds.), Understanding Fitness. How Exercise Fuels Health and Fights Disease. Westport,
CT: Praeger Publishers, 2008.
Chapter Outline
I. Psychophysical Training for General Populations
II. Functional Training for Functional Health
III. Functional Health Evaluation
IV. Exercise Prescriptions for Functional Health
Psychophysical Training for General Populations
P
sychophysical and functional training concepts are gradually
making their way from the rehabilitation and athletic settings
to fitness centers for use by relatively healthy adults. In the
past, functional training has not included psychological concepts, but in
this chapter, as elsewhere in this text, psychophysical training and
functional training are synonymous concepts. The application of these
concepts, however, is not often straightforward. In this chapter we
describe the use of functional training for relatively healthy adult
populations who are training to improve wellness and performance in
activities of daily living, decrease the risks of injury and falls, and prevent
decline in function later in life.
Functional training begins with purpose
Functional training for relatively healthy adults has become a
buzzword applied to training modes that have certain characteristics.
These characteristics include posture and balance, agility, ―core‖ training,
free form resistance training (e.g., medicine balls and elastic bands),
marital arts (e.g., Tai chi, yoga), and choreographed calisthenics. None of
these characteristics, however, makes an exercise program functional. It is
the purpose of exercise, not the type of exercise, that distinguishes
functional training.
200
Functional training is broadly defined as training to improve realworld physical performance, otherwise known as activities of daily living.
These activities of daily living (ADLs) are just that; they are the things
people do on a daily or weekly basis. Some activities are home-based, like
getting out of bed, bathing, gardening, walking up and down stairs,
cooking, lugging grocery bags, carrying children, and housework. Some
activities predominate at work, such as computer use, truck driving, tool
and machine use, assembly work, firefighting and rescue, and any number
of other occupational tasks. Other activities are specific to hobbies or
leisure time activity. People often struggle to do these activities effectively
and without pain, but prior injury or illness, overuse and maladaption to
chronic use, deconditioning, or biological degeneration due to aging, may
make that difficult. Functional training aims at improving either general
movement qualities or specific movement skills so that these movements
become easier, freer, more adaptable, and more comfortable when done in
their real-life context.
Functional training aims to improve functional health
The counterpart to functional training, functional health, is one‘s
capability to participate effectively in wide ranging activities of daily
living, regardless of any underlying pathology or mental or physical
illness. An adaptable motor system characterizes functional health,
enabling a diverse repertoire of movements that permits individuals to
engage in physical activities that are both necessary and desirable
components of a rich and fulfilling life. The purpose of functional training
is foremost to help one develop this repertoire to enable effective
movements with confidence and without discomfort during normal daily
activities at home, work, and play.
This objective of functional training differs from that of
conventional exercise regimens. The purpose of conventional
cardiovascular and muscle fitness training is to enhance the basic
physiological workings of the body, like increasing cardiac output,
boosting cellular metabolism, and hypertrophying muscle tissue. Enhanced
physiological systems are certainly a good thing – improving overall
health and lowering disease risk – but this does not mean an automatic
improvement to function efficiently and relatively pain-free throughout
normal activities of daily life. The relationships among physiological
mechanisms and real-life performance can be better understood by looking
at the model of disablement, a framework sanctioned by the World Health
Organization to track the progression from disease to disability.
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The model of disablement shows the areas targeted for functional training
The model of disablement describes a sequence of debilitating
effects beginning with pathology, and moving toward impairment,
functional limitation, and ending with disability. Pathology, the underlying
disease or physiological abnormality, contributes to impairment in how
tissues or systems operate. These systems may be physiological or
psychological. Impairment contributes to functional limitation, which is
difficulty in performing ADLs. If functional limitation disrupts ability to
function in society, it becomes a disability. The figure below illustrates
that this model is not a simple continuum; for the progression from
pathology to disability is an interaction of multiple factors, and can even
progress backward, as in the case of functional limitations and disabilities
that lead to inactivity and hypokinetic diseases. The same impairment may
result in a functional limitation in one person, a different limitation in
another person, and no impairment in still another. Progression is linked to
the extent of the impairment, the number of other impairments and comorbidities, psychosocial factors, strategies one uses to adapt to
dysfunction, and a host of genetic and acquired risk factors that can
predispose one to more serious consequences.
exercise
medical
functional training
strategies
PATHOLOGY
IMPAIRMENT
FUNCTIONAL
LIMITATION
DISABILITY
Progression along the continuum is mostly left to right (hence the double
arrows), but not always (single arrow). It is not always direct as indicated by the
curved arrows. Numerous risk factors influence if and how one level progresses
to the next. Key risk factors are:
-Demographic (e.g., age, socioeconomic status, education)
-Physiological (e.g., body size, diet, gender)
-Environmental (e.g., housing, climate, occupation)
-Co-morbidities (e.g., hypertension, diabetes, obesity)
Notice the overlap among the medical, exercise, and functional training
interventions, but that functional training targets a broader scope than other
methods. An important target for functional training is the development of
effective strategies to prevent functional limitations from becoming disabilities.
202
The traditional medical and exercise approach addresses problems
primarily at the pathological and impairment level, which potentially can
have a positive effect on functional limitations and disability. This is
certainly the right approach in many instances, but the complexity of
disablement model means that even if a pathology or impairment restores
to normal, the functional limitations and disability may remain. What is
deemed normal or acceptable by rehabilitative standards may still include
a tolerance of asymmetric movement or restricted joint motion that may be
exacerbated with normal use or with a traditional exercise program.
Likewise, often times the pathology or impairment cannot be reversed,
forcing individuals to learn to live with the disabling consequences of
chronic health problems. The functional training approach is designed to
address functional limitations, and to a lesser extent, disability, thereby
improving functional health.
Functional Training for Functional Health
There are two categories of health issues; therapeutic and
preventative, that can benefit from functional training. Therapeutic health
issues are functional limitations brought about by known health problems,
such as osteoarthritis and low back pain. The therapeutic label should not
be misunderstood to mean that the health issues are so bad as to require
medical attention. Many lingering health problems remain after even
successful medical interventions, or are not severe enough for individuals
to believe medical intervention is necessary (e.g., sprained ankle, chronic
low back discomfort). Preventive health issues include strategies to
maximize current performance and minimize risks of future functional
limitations. In this category are generally healthy individuals training for
vocational readiness (work hardening and prehabilitation training),
recreational activity-specific training including that for the weekend
athlete, and those trying to prevent later functional decline, such as with
mobility and fall prevention for older adults. There is considerable overlap
between therapeutic and preventative functional training, as a program can
address both current limitations and prevention of further decline in
function. This is especially true in older adults, who often need to address
current health issues and train to prevent disabling problems like falls.
This situation is illustrated in the case study presented at the end of the
chapter.
Therapeutic: Musculoskeletal and Other Chronic Health
Problems. Therapeutic functional training may improve physical function
and reduce discomfort, even in the face of disease process or damaged
203
tissues that can lead to a number of movement problems. For example,
arthritis, multiple sclerosis, old tissue damage from injury or disease,
cardiovascular disease, and a large number of other chronic health
problems, result in painful and dysfunctional movement patterns that
cascade into more dysfunction and pain. Even minor problems considered
by many to be simply bothersome or just a part of normal aging, like
muscle aches, restricted joint range of motion, and muscle weakness, may
contribute to the cascade of dysfunction and pain. Many of these health
problems are found in the elderly, but by no means are middle aged and
younger adults invulnerable. In fact, it is likely that most adult members of
fitness centers exercise to overcome nagging musculoskeletal problems,
and similar problems run rampant in both blue and white collar
occupational settings.
A large number of scientific studies have reported successful
functional training outcomes. Factory workers have overcome chronic
neck and shoulder musculoskeletal pain, young and middle-aged
individuals have recovered from low back pain and learned to manage
joint pain from prior injury. Knee and ankle injury prevalence have been
reduced in young athletes, carpal tunnel syndrome and other repetitive
strain injuries alleviated in office and factory workers, and better
functioning in daily activities have been reported in sufferers of
osteoarthritis and multiple sclerosis. Functional training has helped
individuals with very poor exercise capacity due to cardiopulmonary
problems to overcome some of their disability through improved
functional strength and efficiency of movement. Seemingly, an impressive
result for sure, but functional training is no cure all. It has also proven
ineffective in many instances where, for example, degenerative or
damaged joint architecture precluded normal joint range of motion.
Preventative: Fall Prevention and Activities of Daily Living.
Numerous reports over the past 20 years generally indicate that fall
prevention programs are effective in relatively healthy elders, and frail and
institutionalized elders suffering from physical and mental impairments.
Often these programs include multiple strategies alongside functional
exercise, like reducing psychotropic drug doses, safety education, and
reduction of environmental risk factors. In recent years there have been
several ―systematic reviews‖ that summarized scientific studies on
functional training. These reviews indicate that functional exercise
programs improve performance on functional laboratory tests (e.g.,
walking speed, grip strength, rising out of a chair), but real world
performance like reducing the number of falls, has been difficult to
measure. Even Tai Chi, widely popularized over the past 15 years in part
204
due to a few studies that showed large benefits for improving elderly
mobility, has not shown to produce consistently positive effects. Part of
the problem, as concluded by researchers like Verhagen and her colleagues
at the Erasmus Medical Center in Rotterdam, is simply that many of these
scientific studies do not sufficiently tease out the complexities that
contribute to functional declines. Researchers do agree that effective
exercise training programs tend to be multimodal (e.g., strength and
balance and gait training) and individually targeted. The success of a
functional training program hinges largely on the ability of the program
exercises to carry-over to real-life activities.
If there is one thing that has emerged from the science, it is that
there is a great deal of individual variation in how one responds to training
and how training adaptations transfer to the real world. Some individuals
show remarkable improvements whereas others doing the same training
program show none. This stands in contrast to standard fitness programs in
which the vast majority of participants who engage in the same exercise
mode of sufficient intensity realize some physiological improvements.
This illustrates that most scientific studies of functional training lack the
essential ingredient of providing individual based training prescriptions.
Prominent geriatric exercise physiologist, Jack Rejeski, Ph.D, and his
fellow scientists at Wake Forest University noted the that it is difficult to
prescribe a standardized functional training programs, and assert that the
large role sociocultural factors play in influencing real world performance
is often overlooked. These scientists believe that functional training
programs must, within the actual context of training, address beliefs and
symptoms that influence how one performs physical tasks.
Functional Health Evaluation
Effective functional training requires careful client evaluation and
observation to determine the individual needs of the client, the goals of the
functional training program, and the exercise techniques to accomplish
those goals. Unfortunately, there is no one-size-fits-all or gold standard of
testing because the functional impairments and needs vary widely across
individuals and populations. Thus, ingredients for an effective functional
training program, whether therapeutic or preventative, should satisfy the
following criteria to improve functional health; (1) identify individual
needs, (2) application to real-world physical challenges, (3) appropriate for
current level of physical function, (4) systematic increase in physical
challenge, and (5) accessible for user in the environment in which the user
205
is most likely to function. Of course, these criteria fit precisely within the
dynamic systems model of the individual, the task, and the environment.
The functional health evaluation begins with individual needs
Identification of individual needs begins with a functional health
evaluation. The part of the process is the most challenging, in part because
the majority of functional health evaluation protocols (also called
functional performance evaluation) have been developed and used for
unhealthy persons (physical rehabilitation and frail elders) and for specific
vocational settings, and may not work well for relatively healthy adults.
Nevertheless, by looking at the functional health evaluation process
several general strategies for use in relatively healthy populations can be
found.
Functional health evaluation aims at understanding what
movements and tasks are dysfunctional, why that movement is
dysfunctional, how the individual deals with it, and finally, the goals of the
individual. Typically, this includes a subjective assessment of the client
based on questionnaires, medical history and quality of life (what, how and
why of client‘s current state); an objective assessment of the client based
on functional performance tests (what can/can‘t client do?); and finally,
interpretation of subjective and objective information to evaluate degree of
limitation and identification of goals.
Functional performance assessment for relatively healthy middle
aged adults and high functioning elders is scarce, but there have been some
attempts to provide guidelines in testing these individuals based on
modifications to functional training assessments for frail and unhealthy
adults. Because low back pain is such a common condition among adults
who consider themselves otherwise healthy, it is appropriate to assess risk
factors for low back pain.
Initial health screening begins with a medical history and a general
assessment of the client‘s health-related quality of life, such as the SF-36.
The SF-36 questionnaire measures eight dimensions from physical
functioning and bodily pain to mental health and social functioning.
Results from the initial screening may indicate the need for functional
performance testing, but even if not, administering a limited number of
general functional performance tests that have a sound basis for prediction
of later functional limitations, is prudent. The functional performance test
batteries provided here have reasonable test reliability, plausible validity to
predict later disability, and are able to discriminate between higher
functioning and moderate functioning individuals, and older versus
206
younger people. These tests focus on strength of the arms and legs,
postural control, balance, and gait. They are described here with criterion
values purposely omitted, only to help the reader understand the nature of
the tests, because the actual testing and interpretation of the results
requires some level of knowledge. Careful observation of movement
quality during test performance is also essential. Stuart McGill, Ph.D., a
spine biomechanist at the University of Waterloo, and author of what may
be the evidence-based bible of low back function, Low Back Disorders;
Evidence-Based Prevention and Rehabilitation, has devised several low
back screening tests. One of his simpler tests, also listed with reference
values, again, is for informational purposes only.
Functional Test Batteries for Relatively Healthy Adults
General Functional Performance
General Functional Performance (Suni et al., Arch
(Curb et al., J Am Geriatr Soc., 54:737-742, 2006)
Phys Med Rehabil, 79:559-569, 1998)
- Balance: unassisted single-leg stand, arms
crossed (seconds)
- Balance: computerized platform, foam pad,
eyes closed (computer measures of sway)
- Leg Strength: knee flexion/extension strength
(isometric)
- Arm Strength: elbow flexion/extension
strength (isometric)
- Hand Strength: grip dynamometer (isometric)
- Leg Strength/Endurance: chair stands (10
timed stands, no arm use)
- Walking Function: rapid 10 foot walk
(seconds)
- Walking Function/Aerobic: 6-minute walk
(distance)
- Balance: one leg stork stand balance, eyes
open (up to 60 s)
- Muscle Endurance: back extension (time up
to 4 minutes)
- Leg Strength: one-Leg squat/lunges (with up
to 30% of bodyweight)
- Arm Strength: modified push ups (# of
pushups in 40s
- Leg Power: jump and reach (jump height in
cm)
- Hip Flexibility: hamstring stretch (leg flexion
range of motion)
- Flexibility: side bending; left and right (cm)
- Walking Function/Aerobic: 2 km walk test
(time and heart rate to predict V02max)
Low Back Function
(McGill, Low Back Disorders: Evidence-Based Prevention and
Rehabilitation, Human Kinetics, 2002)
Right side bridge
Left side bridge
Extension
Flexion
Flex/Ext ratio
RSB/LSB ratio
RSB/Ext ratio
LSB/Ext ratio
Men
95 s
99 s
161 s
136 s
.84
.96
.58
.61
Women Concern*
75 s
78 s
185 s
134 s
.72
> 1.0
.96
.40
> 0.75
.42
> 0.75
*Unbalanced ratios suggest unbalanced muscle
endurance, which may indicate problem areas
Note: these data are from young adults of average
age of 21. These numbers may not apply well to
middle-aged and senior adults.
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In summary, functional testing for unhealthy adults, and relatively
healthy or frail older adults, requires knowledge and familiarity with
functional assessment, to identify the appropriate testing methods, conduct
the tests reliably and safely, and interpret the tests correctly. Functional
health testing for healthy middle aged and highly functioning older adults
is still in the developmental stage, but some gait, posture, and muscle
function tests hold promise in providing guidelines for functional exercise
prescription.
Exercise Prescription for Functional Health
Numerous exercise regimens have been passed on as functional
training, but exercise mode is only important if it satisfies a functional
purpose. Training to improve functional task outcomes requires
understanding of the movements, environments, and circumstances in
which activities are performed. Functional training brings the situational
needs and constraints of the actual activity into the training environment
and creates situations where there can be both training overload and
exaggerated situational needs and constraints. Only by incorporating
environmental situations and task demands into the training program can
training be considered truly functional.
Taken collectively, functional training for fall prevention, general
mobility, specific ADLs can be addressed by basic fitness, functional
mobility challenge training, and self-efficacy improvement. Functional
training aimed at overcoming specific musculoskeletal and chronic health
problems requires additional steps to train movement patterns that
alleviate discomfort and avoid making the problem worse. This step
requires more than can be covered here, and so we will focus on the three
basic steps.
Basic fitness must come first when dealing with unfit and frail persons
First addressed are the basic components of fitness (strength,
aerobic, flexibility), particularly in frail older adults and others who are
highly deconditioned. The specific fitness demands of the task are
emphasized while also taking into consideration impairments shown to be
strongly associated with later functional declines. Leg and arm strength are
important components of many tasks; and a lack of strength is implicated
in many functional declines, and thus can be a starting point for many
functional training programs. General mobility and movement training is
then added, with increasing level of challenge, variability, and uncertainty
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to focus on functional needs. The purpose of this functional ―mobility
challenge‖ training is to enhance the response to balance threats that are
necessary for real-life environments, develop adaptable and responsive
postural control strategies, improve movement ease and effectiveness, and
develop self-efficacy. The strategies devised in the mobility challenge
training draw upon the environmental and task issues illustrated in Figure
5 and the functional impairments revealed through testing. Examples
include walking over obstacles and on unstable or slippery surfaces,
asymmetric load carrying while pivoting, ―speed‖ walking against the flow
of foot traffic, reduced lighting, dual task challenges like engaging in a
conversation while walking, reaching and stretching while walking, and
combinations of the above. These first two tiers of the framework address
the multiple biological and functional problems associated with falls and
mobility problems.
Development of self-efficacy is often ignored. It should be
incorporated into the entire functional training package to facilitate
transfer of the training to real life circumstances, and the sociocultural
environment. Self-efficacy, or one‘s belief in their competence to perform
or carry out tasks, is an important contributor to functional health and selfregulation of health behaviors like adherence to training. Understanding
the self-efficacy beliefs of individual clients requires purposeful inquiry
and careful observation and is a vital aspect of assessing the functional
training needs in elders and those with low back pain and other chronic
health problems. Training for self-efficacy may include educational
sessions or just a careful progression of exercise challenges that develop a
sense of mastery and empowerment in the clients.
Notes on Posture and Balance Training. Posture and balance
training are important components of many functional training programs,
but often misunderstood and misapplied. A variety of different balance
training exercises appear to be effective in training better automatic
postural control, but like most functional training methods, the techniques
are specific to the desired movement outcome and the individual‘s
psychological and physiological characteristics. For example, jumping and
landing training that emphasizes biomechanically stable landings can help
prevent some knee and ankle injuries, but computerized balance training
may not. Some types of back exercises – with and without psychosocial
interventions – have been successful in reducing low back pain, as have
some mental imagery training programs. Movement training and postural
awareness approaches can be successful in helping office workers alter
their movements and thereby reduce repetitive strain injuries to the wrists
and shoulders, but sitting on a Swiss ball probably will not. The important
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similarity among successful posture and balance techniques is inclusion of
training that mimics actual task demands and environmental challenges.
Functional training is appropriate for healthy adults as well
What about functional training for healthy adults with no
functional limitations? Can non-specific functional training prevent
widespread functional decline in later years? The current trend in posture
and balance training for healthy adults, such as wobble board balance
exercises, Swiss ball training, and low intensity martial arts, certainly aims
in this direction. However, it is unlikely that non-specific training will
prevent multiple potential deficits. Generic postural training may enhance
some balance mechanisms that contribute to some functional limitations.
In addition, there is evidence that a challenging balance program may help
maintain some sensory-motor systems (e.g., vestibulo-motor), and slow
the development of impairments. To some extent, fitness training aimed at
overcoming impairments (e.g., strength, stamina, flexibility, agility) can
include functional challenges. In this way, fitness becomes integrated with
motor skills and postural control and thus, more useful. Even if functional
improvement is secondary to fitness training, it is still best to target the
functional training toward prevalent functional health problems that are
likely to arise. These prevalent health issues include fall prevention and
limitations arising from back and shoulder musculoskeletal problems.
There is no preferred mode, alone or in combination of other
techniques, of training. Tai Chi may help prevent falls in some elders,
strength training may be a better solution for others, and gait challenge
training better for someone else. Body awareness and posture training has
been shown to help workers overcome neck and shoulder pain at work, but
then, so has relaxation training and some forms of strength training. In
some workers these interventions have had no success. Unfortunately,
even a rational and evidenced-based functional training program may end
up being ineffective. If so, it is necessary to approach the problem from a
different perspective and try again. Regardless, awareness and intention of
the client to apply functional training concepts in all aspects of daily life
are important ingredients for success.
Summary and Application
Functional training is truly only functional if it addresses
psychophysical and functional health needs. As in sport and rehabilitation
based training, functional training begins with assessing individual needs
210
taking into account environmental and task specific constraints. Assessing
functional needs and functional health can be challenging for relatively
healthy persons, but there is a small but growing body of evidence that
these persons can engage in preventative functional training to at least
delay or reduce eventual functional decline.
Though exercise programs should begin with basic fitness in order
to improve general health and physical capabilities, exercise programs
should progress to more functional programs aimed at improving specific
functional performance measures. It is important that these programs,
particularly for those with functional decline, aim at improving selfefficacy.
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