Chapter 5
Impairment In Muscle
Performance
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Definitions
Strength – The maximum
force that a muscle can
develop during a single
muscle contraction, and
is the result of complex
interactions of neurologic,
muscular, biomechanical,
and cognitive systems.
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Definitions (cont.)
Force – Agent that produces or tends to produce a
change in the state of rest or motion of an object.
Kinetics – Study of forces applied to the body.
Torque – The ability of a force to produce rotation.
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Moment Arm
Perpendicular distance from the line of action of
the force to the axis of rotation.
Axis
Moment arm
Vector of force
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Torque can be altered by
1. Changing the force
magnitude
2. Changing the moment arm
length
3. Changing the angle b/t the
direction of force and
momentum
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Power and Work
Power – Rate of performing work.
Work – Magnitude of force acting on an
object multiplied by the distance
through which the force acts.
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Endurance
The ability of a muscle to sustain forces
repeatedly or to generate forces over a
certain period.
Evaluate using:
Isometric contractions
Repeated dynamic contractions
Repeated contractions using isokinetic
dynamometer
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Muscle Actions
Isometric – contraction w/o motion
about an axis (force is product)
Dynamic (NOT isotonic) – Concentric
(shortening contraction), eccentric
(lengthening contraction)
Isokinetic – Concentric or eccentric w/
constant velocity
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Morphology and Physiology of Muscle
Performance
Improving muscle
performance often
translates into
improvements in
functioning by the
patient.
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Gross Structure of Skeletal Muscle
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Ultrastructure of Skeletal Muscle
Sarcomere – Functional unit of
contractile system in muscle.
A
Z
H
I
Relaxed Sarcomere
Titin
Myosin
Actin
Contracted Sarcomere
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Events During Contraction and
Relaxation
1. Depolararization of T-tubules – release of Ca2+
from SR.
2. Calcium binds to troponin/tropomyosin
complex.
3. Actin combines with myosin-activated myosin
ATPase. ATP splits, energy produces power
stroke of X-bridges – tension is created.
4. ATP – binds to myosin X-bridge, allowing Xbridge to dissociate from actin.
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Events During Contraction and
Relaxation (cont.)
5. X-bridging activation continues as long as Ca2+
concentration is high enough to inhibit action of
troponin/tropomyosin complex.
6. When stimulation ceases, Ca2+ returns to SR.
7. Removal of Ca2+ restores inhibitory action of
troponin/tropomyosin. In the presence of ATP,
actin and myosin remain in the relaxed state.
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Muscle Fibers
I
Tonic
SO
Slow Oxidative
S
Slow
II A
FO
Fast Oxidative
FR
Fast Fatigue
Resistant
II AB
FOG
Fast Oxidative
plus Glycolytic
FI
Fast Intermediate
Fatigueability
II B
FG
Fast Glycolytic
FF
Fast Fatigueability
Strength is related to fiber diameter, not type. Type I fibers typically have smaller
diameter than type II fibers.
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Factors Affecting Muscle Performance
1. Fiber type
2. Fiber diameter
3. Muscle size
4. Force – velocity relationship:
Active force continually adjusts to the speed
at which the contractile system moves.
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Length–Tension Relationship
Capacity to produce force depends
on the length at which muscle is
held with maximum force delivered
near the muscle’s normal resting
length.
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Changes in Numbers of Sarcomeres
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Positional Strength
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Muscle Architecture
1. The force the muscle can produce is directly
proportional to the cross-sectional area (more
sarcomeres in parallel).
2. The velocity and working excursion of the
muscle are proportional to the length of the
muscle (more sarcomeres in series).
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More Factors Affecting Muscle
Performance
Training Specificity – Muscle responds to the
specific ROM, posture, type in which it’s
trained.
Neurologic Adaptation – Initial increase in
strength is neural adaptation (2–4 weeks).
Muscle Fatigue – Dosage of resistive exercise
is limited to “form fatigue” (sacrifice of
technique).
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Lifespan Considerations
Prepuberty
20% of child’s body mass is muscle.
Benefits of exercise – improved muscle, motor
performance, body composition, sense of wellbeing.
Moderate resistance training is acceptable.
Heavy resistance should be avoided.
Focus on neurologic aspects of training.
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Puberty
Body composition changes to 27–40% of body
mass.
Onset of puberty, strength of boys and girls
diverges remarkably.
General strength training is recommended.
Avoid heavy loads (epiphyses remain vulnerable
to injury).
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Early Adulthood
Biologic structures are in a state of
excellent adaptability.
Emphasis should be based on balanced
fitness program for cardiopulmonary
fitness, muscle performance, and flexibility.
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Middle Age
Decrement of strength must be differentiated.
Training for as little as 2 hours per week can
positively influence strength.
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Advanced Age
Possible to reverse muscular weakness in
old age.
Resistive exercise should be directed
toward muscles susceptible to atrophic
changes.
Training considerations should include
power and strength.
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More Factors Affecting Muscle
Performance
Cognitive aspects of
performance
Effects of alcohol
Effects of corticosteroids
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Causes of Decreased Muscle
Performance
Neurologic pathology
Muscle strain
Disuse and conditioning
Length-associated changes
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Physiologic Adaptations to Resistive
Training
Improvement in muscle
performance
Positive effects on
cardiovascular system,
connective tissue, and bone
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Possible Physiologic Adaptations to
Resistive Exercise
Muscle – in fiber size and mitochondrial
density
Connective tissue – ligament and tendon
strength and collagen content may
Bone – density may
Cardiovascular system – HR, systolic and
diastolic BP, cardiac output and VO2 max,
cholesterol
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Examination and Evaluation of Muscle
Performance
Tests include an analysis of functional muscle strength
Manual muscle testing (consider imbalances,
length–tension relationships, and positional
weakness when choosing positions)
Handheld dynamometers
Isokinetic dynamometers
Dynamic strength test
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Therapeutic Exercise Intervention for
Impaired Muscle Performance
Enhancing performance via therapeutic
exercise is at the core of the intervention
program for many patients.
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Activities to Increase Muscle
Performance
Isometric Exercise (provides strength base
for dynamic exercise)
Dynamic Exercise (weight machine
exercise, free-weight exercise, plyometric
exercise)
Isokinetic Exercise (provides maximum
resistance throughout entire ROM)
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Dosage – Intensity, Duration,
Frequency, Sequence
Intensity – Perform exercise to substitution of
form fatigue.
Duration – Vary rest intervals dependent upon
volume (total repetitions) and rest intervals.
Frequency – Depends on rehab goals.
Sequence –Affects the development of strength.
Rehab generally specific isolation training and
graduate to multi-joint exercises, small-large
movements.
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Dosage Varies
Strength Training – 60–70% of
1RM, 8–12 reps.
Power Training – 1–3 sets 30–60%
of 1RM.
Endurance Training – 10–15 reps,
10–25 reps (advanced). Shorter
rest periods.
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Precautions and Contraindications
Avoid use of valsalva maneuver.
Use isometrics with caution (persons at risk –
high BP).
Overtraining/overwork (may lead to mood
disturbances).
Caution should be used with prepubertal,
pubertal children and adolescents (minimize
stress to epiphyseal sites).
Acute or chronic myopathy (exercise is
contraindicated).
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Summary
 Muscle performance = strength, power, and
endurance.
 Clarify when using “strength” as a qualifier in
terms of force, torque, and work.
 Muscle actions – static and dynamic.
 Muscle morphology – thorough knowledge is
needed for appropriate prescription of
intervention.
 Force gradation occurs by rate coding and size
principles.
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Summary (cont.)
 Overload training – changes in hypertrophy
(primarily) and hyperplasia.
 Strength – must be evaluated relative to
muscle length.
 Specificity of training exists.
 Adaptation to training – initially neurologic and
precedes morphologic changes.
 Form fatigue – point at which individual must
discontinue exercise or sacrifice technique.
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Summary – (cont.)
 Resistive training – dose and goals differ.
Beneficial late childhood through old age.
 Impaired muscle performance – results from
neurologic pathology, muscle strain, disuse, or
length-associated changes.
 Adaptations to resistive exercise include bone,
connective tissue & cardiovascular system.
 Activities to improve muscle performance –
isometric, dynamic, plyometric, and isokinetic
exercise.
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Summary – (cont.)
 Dynamic exercise may include free weights,
resistive bands, pulleys, weight machines, or
body weight.
 Contractions during exercise include
concentric, eccentric, and combinations
thereof.
 Dosage of exercise depends on the goal.
 Precautions and contraindications must be
known to ensure safety.
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