The Role of Muscles
Applied Kinesiology
420:151
Agenda
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Introduction to muscles
Attachments
Structural classification
Types of muscle action
Factors affecting muscle function
Coordination of muscles
Types of movements
Introduction to Muscles
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Movement occurs via:
Internal force
External force. Examples?
Introduction to Muscles
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Properties of skeletal muscle:
Extensibility
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Contractility
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50% decrease
Only muscle
Elasticity
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50% increase
Tendons too
Tendons too
Irritability
Agenda
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Introduction to muscles
Attachments
Structural classification
Types of muscle action
Factors affecting muscle function
Coordination of muscles
Types of movements
Attachments
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How does skeletal muscle attach to
bones?
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Directly?
Connective tissue coverings (tendon)
Tendons:
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Round cord, flat band, aponeurosis
Embedded within bone
Attachments
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Origin and insertion
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Tendon length
Stability/mobility tendency
Proximal/distal tendency
Proximal and distal attachment
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Less error
Example (arm curl vs chin-up)
Attachments
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More terms
Extremities: Proximal and distal
Diaphragm: Peripheral and central
Head/Neck/Trunk:
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Vertical lines of pull: Upper and lower
Horizontal lines of pull: Medial and lateral
Agenda
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Introduction to muscles
Attachments
Structural classification
Types of muscle action
Factors affecting muscle function
Coordination of muscles
Types of movements
Structural Classification
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Fiber arrangement
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Longitudinal
Quadrate
Triangular (radiate)
Fusiform
Unipenniform
Bipenniform
Multipenniform
Longitudinal
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Structure:
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Long
Strap-like
Consistent diameter
Examples:
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Sartorius
Rectus abdominis
Figure 8.7
Quadrate
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Structure:
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Four-sided
Usually flat
Examples:
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Pronator quadratus
Rhomboid
Figure 3.3
Triangular (Radiate)
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Structure:
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Fibers radiate from
narrow to broad
attachment
Examples:
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Pectoralis major
Gluteus medius
Figure 3.3
Fusiform
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Structure:
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Rounded
Tapered endings
Examples:
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Biceps brachii
Brachialis
Figure 3.3
Unipenniform
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Pennate  Feather
Structure:
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Series of short parallel
fibers
Feather-like arrangement
from side of tendon
Examples:
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Extensor digitorum
longus
Tibialis posterior
Figure 3.3
Bipenniform
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Structure:
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Similar to
unipenniform
Two sets of fibers
Examples:
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Flexor hallucis
Rectus femoris
Figure 3.3
Multipenniform
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Structure:
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Similar to
bipenniform
Multiple tendons
Examples:
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Middle deltoid
Marieb & Mallet, 2001, Figure 11.3
Effect of Fiber Arrangement
on Force Output
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Concept #1: Force directly related to
cross-sectional area  more fibers
Example: Thick vs. thin
longitudinal/fusiform muscle?
Example: Thick fusiform/longitudinal vs.
thick bipenniform muscle?
Concept #2: As degree of pennation
increases, so does # of fibers per CSA
Agenda
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Introduction to muscles
Attachments
Structural classification
Types of muscle action
Factors affecting muscle function
Coordination of muscles
Types of movements
Types of Muscle Action
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Contraction vs. action
Concentric
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Eccentric
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Internal = external = 0 work
Isotonic
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External > internal = - work
Isometric
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Internal > external = + work
Is this really possible?
Isokinetic
Agenda
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Introduction to muscles
Attachments
Structural classification
Types of muscle action
Factors affecting muscle function
Coordination of muscles
Types of movements
Factors Affecting Muscle
Function
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Line of pull
Angle of attachment
Length-tension relationship
Force-velocity relationship
Stored elastic capabilities
Line of Pull
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The direction of any movement caused by a
muscle is due to:
#1: Joint structure
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Example: Elbow flexion (biceps brachii) vs. knee
extension (rectus femoris)
#2: The relation of the line of pull to the joint
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Example: Upper fibers pectoralis major as
abductor/adductor
The location of the line of pull in
relation to the joint center determines
the movement in this case
Figure 3.4
Angle of Attachment
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The angle of attachment affects the
efficiency of the movement
Internal forces have two components
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Rotary force
Parallel force
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Stabilizing
Dislocating
Parallel forces do not cause movement
therefore reduce efficiency
Perpendicular
No Parallel Force
Stabilizing or
dislocating?
Maximum
efficiency
Hamill & Knutzen, 2004, Figure 3.23
Stabilizing or
dislocating?
More or less?
Hamill & Knutzen, 2004, Figure 3.23
Length-Tension Relationship
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Optimal length rule  Slightly longer
than maximum resting length
Too short  no force  why?
Too long  no force  why?
Active + Passive
Optimal?
Active
Too long?
Too short?
Passive
Figure 3.7
Force-Velocity Relationship
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Concentric actions
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Inversely related
Vmax = F0  vice-versa
Why? Cross-bridges take time
Eccentric actions
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Directly related until . . .
Figure 3.8
Stored Elastic Capabilities
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Rapid stretch  concentric action =
more work
Why? Stored elastic energy
As speed increases so does effect
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Up to a certain point
Addition of stretch reflex  SSC
Agenda
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Introduction to muscles
Attachments
Structural classification
Types of muscle action
Factors affecting muscle function
Coordination of muscles
Types of movements
Coordination of Muscles
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Role of muscles
Biarticular muscles
Role of Muscles
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Agonists
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Synergists
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Directly responsible for movement
Stabilizers
Neutralizers
Antagonists
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Reciprocal inhibition
Braking
Synergists as Stabilizers
Support of limb  Deltoid example
Figure 3.9
Synergists as Neutralizers
Pectoralis minor and serratus anterior
Biarticular Muscles
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Proximal/distal attachments cross 2
joints
Not long enough for full ROM
Result? Tension of one biarticular
muscle transferred to opposite muscle
Example: Hamstrings and rectus
femoris
Advantage over monoarticular muscles?
Concurrent Movement
Biarticular Muscles
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Concurrent vs. countercurrent
movements
Maximum ROM
Passive/active insufficiency
Agenda
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Introduction to muscles
Attachments
Structural classification
Types of muscle action
Factors affecting muscle function
Coordination of muscles
Types of movements
Types of Movements
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Passive
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Active:
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Example: Partner stretch or falling to ground
Slow  Constant force = inefficient
Rapid  Ballistic = efficient
How to stop ballistic movement
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Antagonist
Passive resistance of connective tissue and
eccentric action
External object
Review
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The muscle fiber (pp. 46-48)
Fast vs. slow twitch (pp. 48)