chapter 5 impairment in muscle performance

Copyright 2005 Lippincott Williams & Wilkins

Chapter 5Impairment In Muscle

Performance


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.


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.


Moment Arm

Perpendicular distance from the line of action of the force to the axis of rotation.

Axis

Moment arm

Vector of force


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


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.


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


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


Morphology and Physiology of Muscle Performance

Improving muscle performance often translates into improvements in functioning by the patient.


Gross Structure of Skeletal Muscle


Ultrastructure of Skeletal Muscle

Sarcomere – Functional unit of contractile system in muscle.

Z AH I

Actin MyosinTitin

Relaxed Sarcomere

Contracted Sarcomere


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.


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.


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.


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.


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.


Changes in Numbers of Sarcomeres


Positional Strength


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).


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).


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.


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).


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.


Middle Age

Decrement of strength must be differentiated.Training for as little as 2 hours per week can

positively influence strength.


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.


More Factors Affecting Muscle Performance

Cognitive aspects of performance

Effects of alcoholEffects of corticosteroids


Causes of Decreased Muscle Performance

Neurologic pathologyMuscle strainDisuse and conditioningLength-associated changes


Physiologic Adaptations to Resistive Training

Improvement in muscle performance

Positive effects on cardiovascular system, connective tissue, and bone


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


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


Therapeutic Exercise Intervention for Impaired Muscle Performance

Enhancing performance via therapeutic exercise is at the core of the intervention

program for many patients.


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)


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.


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.


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).


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.


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.


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.


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.

chapter 5 impairment in muscle performance

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