Download - Chapter 5 Impairment In Muscle Performance
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Chapter 5Impairment In Muscle
Performance
Copyright 2005 Lippincott Williams & Wilkins
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 magnitude2. Changing the moment arm
length3. 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 contractionsRepeated dynamic contractionsRepeated 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.
Z AH I
Actin MyosinTitin
Relaxed Sarcomere
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 X-bridge 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 FibersI
TonicSO
Slow OxidativeS
Slow
II A FOFast Oxidative
FRFast Fatigue
ResistantII AB FOG
Fast Oxidative plus Glycolytic
FIFast Intermediate
FatigueabilityII B FG
Fast GlycolyticFF
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 type2. Fiber diameter3. Muscle size4. 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 well-being.
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 alcoholEffects of corticosteroids
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Causes of Decreased Muscle Performance
Neurologic pathologyMuscle strainDisuse and conditioningLength-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 strengthManual muscle testing (consider imbalances,
length–tension relationships, and positional weakness when choosing positions)
Handheld dynamometersIsokinetic dynamometersDynamic 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.