Measuring
Musculoskeletal
Fitness (Chapter 7)
PE 254
Human Body Muscle Diagram
Behavioral Properties of the
Musculotendinous Unit

Behavioral properties of muscle tissue:
◦
◦
◦
◦

Extensibility
Elasticity
Irritability
Ability to develop tension
Behavioral properties common to all
muscle:
◦ Cardiac, smooth, skeletal
Extensibility and Elasticity
Extensibility
 Elasticity
 Two components:

◦ Parallel elastic component (PEC)
◦ Series elastic component (SEC)
Contractile component
 Visoelastic (Having flow-resistive as well
as stretchy properties)

Irritability and the Ability to
Develop Tension

Irritability
◦ The ability to respond to electrical or
mechanical stimulus.
◦ Response is the development of tension.
 Not necessarily a contraction
Structural Organization of Skeletal
Muscle

Human body has approx. 434 muscles
◦ 40-45% of total body weight in adults
◦ 75 muscle pairs responsible for bodily
movements and posture
Muscle Fibers
 Motor Units
 Fiber Types
 Fiber Architecture

Muscle Fibers
Contain:
sarcolemma
sarcoplasm
nuclei
mitochondria
myofibrils
myofilaments
Sarcomere
Z lines
M line
A band
myosin filaments
I band
actin filaments
H zone
Motor Units
Fiber Types




Fast Twitch (FT)
◦ Type IIa
◦ Type IIb
Slow Twitch (ST)
◦ Type I
Peak tension reached in FT in 1/7 time of ST
ST and FT compose skeletal muscles
◦ Percentages of each range from muscle to muscle and
individual to individual.
Slow Twitch (Type I)
The slow muscles are more efficient at using oxygen to generate more fuel (known as ATP)
for continuous, extended muscle contractions over a long time. They fire more slowly than
fast twitch fibers and can go for a long time before they fatigue. Therefore, slow twitch
fibers are great at helping athletes run marathons and bicycle for hours.
Fast Twitch (Type II)
Because fast twitch fibers use anaerobic metabolism to create fuel, they are much better at
generating short bursts of strength or speed than slow muscles. However, they fatigue
more quickly. Fast twitch fibers generally produce the same amount of force per
contraction as slow muscles, but they get their name because they are able to fire more
rapidly. Having more fast twitch fibers can be an asset to a sprinter since she needs to
quickly generate a lot of force.
Type IIa Fibers
These fast twitch muscle fibers are also known as intermediate fast-twitch fibers. They can
use both aerobic and anaerobic metabolism almost equally to create energy. In this way,
they are a combination of Type I and Type II muscle fibers.
Type IIb Fibers
These fast twitch fibers use anaerobic metabolism to create energy and are the "classic"
fast twitch muscle fibers that excel at producing quick, powerful bursts of speed. This
muscle fiber has the highest rate of contraction (rapid firing) of all the muscle fiber types,
but it also has a much faster rate of fatigue and can't last as long before it needs rest.
Fiber Types

Effects of training:
◦ Endurance training can increase ST
contraction velocity by 20%
◦ Resistance training can convert FT fibers from
Type IIb to Type IIa
Elite athlete fiber type distribution does
not significantly differ from untrained
individuals
 Affected by:

◦ Age and Obesity
Recruitment of Motor Units
CNS enables matching of speed and
magnitude of muscle contraction to
requirement of movement.
 Threshold activation

◦ ST activated first (low threshold)
◦ With an increase in speed, force, and/or
duration requirement, higher threshold motor
units are activated (FT fibers)
Change in Muscle Length with
Tension Development

Concentric
◦ Bicep shortening with the bicep curl (flexion)

Isometric
◦ Body builders develop isometric contraction
in competition

Eccentric
◦ Acts as a breaking mechanism to control
movement
Roles Assumed by Muscles

Agonist
◦ Primary & Secondary
Antagonist
 Stabilizer
 Agonists and Antagonists are typically
positioned on opposite sides of a joint.

Muscular Strength, Power, and
Endurance
Muscular Strength
 Muscular Power
 Muscular Endurance
 Muscular Fatigue
 Effect of Muscle Temperature

Factors Impacting Force Production
 Torque: turning
effect of an eccentric force
◦ T= Applied Force * Force Arm
 Force arm is the perpendicular distance between
the applied force and the axis of rotation
 Eccentric
force: applied in a direction not
in line with center of rotation of nonmoving axis
Muscular Strength
The ability of a given muscle group to
generate torque at a particular joint.
 Two orthogonal components:

◦ 1) Rotary Component
◦ 2) Parallel to bone

Derived from:
◦ amount of tension the muscles can generate
moment arms of contributing muscles with
respect to joint center.
Muscular Power
The product of muscular force and the
velocity of muscular shortening.
 The rate of torque production at a joint
 Max. power occurs at:

◦ approx. 1/3 max. velocity, and
◦ approx. 1/3 max concentric force

Affected by muscular strength and
movement speed
Muscular Endurance

The ability to exert tension over a period
of time.
◦ Constant: gymnast in iron cross
◦ Vary: rowing, running, cycling
Length of time dramatically effected by
force and speed requirements of activity.
 Training involves many repetitions with
light resistance.

Muscular Fatigue
Opposite of endurance
 Characteristics:

◦ Reduction in force production
◦ Reduction in shortening velocity
◦ Prolonged relaxation of motor units between
recruitment

Possible causes?
Modes of Exercise
Isotonic: alternating concentric and eccentric
muscle activation that moves a body part through
an arc of motion against resistance
 Isokinetic: exercise that involves specialized
equipment that provides "accomodating
resistance" so that the joint moves at a constant
angular velocity
 Isometric: muscle action that is performed against
resistance at any point in a joint's range of motion,
for periods of 5-10 seconds, and that produces no
joint movement
 Plyometric: exercise that requires eccentric
activation of muscles against a resistance, followed
by a brief amortization period, followed by
concentric activation

Overload

Overload induces muscles to adapt,
to increase their ability to generate
force.

Once muscles have adapted to
overload, the overload stimulus
must be increased to produce
further training effects (progressive
overload).
Effect of Muscle Temperature
Increased body temperature, increases
speed of nerve and muscle function
 Fewer motor units needed to sustain
given load
 Metabolic processes quicken
 Benefits of increased muscular strength,
power and endurance
 Key point: Be sure to warm-up!

Common Muscle Injuries

Strains
◦ Mild, moderate or severe

Contusions
◦ Myositis ossificans (A condition in which calcium,
and eventually bone, become deposited in muscle;
often the quadriceps)
Cramps
 Delayed-Onset Muscle Soreness (DOMS)
 Compartment Syndrome (A painful condition

caused by increased pressure within a muscle
compartment)
Brzycki's equation to determine
max load

The Brzycki equation is as follows:
Weight ÷ [1.0278 - ( 0.0278 ×
Number of repetitions ) ]
Group Activities

Muscular training for athletes for 2012
Summer Olympics:
Boxing
Volleyball

Soccer
Rowing
Gymnastics
Wrestling
Apply: Frequency, Intensity, Time, and Type(s)



Agonist muscles
◦ Primary & Secondary
Antagonist muscles
Stabilizer muscles
Video Segments
http://www.youtube.com/watch?v=4dAfseVa
qUw
 http://www.videojug.com/interview/musclefitness-2

Monday, October 12th

Please meet at the Fitness Lab (PE 2A) for
muscular endurance/strength activities.