Chapter 5 Impaired Muscle Performance

1. Chapter 5 Impaired MusclePerformance

2. 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.

3. 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. Torque = Force X Moment arm

4. Moment Arm Perpendicular distance from the line of action of the force to the axis of rotation. Axis Moment arm Vector of force

5. Torque can be altered by • Changing the force magnitude • Changing the moment arm length • Changing the angle b/t the direction of force and momentum

6. 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. Power = Work/Time Work = Force X Distance

7. 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

8. 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

9. 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.

10. Muscle Fibers Strength is related to fiber diameter, not type. Type I fibers typically have smaller diameter than type II fibers.

11. 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. Emphasis of therapeutic exercise intervention should be on restoring normal length and tension development at appropriate point in the range, rather than just strengthening the muscle.

12. Changes in Numbers of Sarcomeres

13. Positional Strength

14. Muscle Architecture • The force the muscle can produce is directly proportional to the cross-sectional area (more sarcomeres in parallel). • The velocity and working excursion of the muscle are proportional to the length of the muscle (more sarcomeres in series). Muscles w/ shorter fibers and a larger cross sectional area – designed to produce force Muscles w/ long fibers – designed to produce excursion and velocity.

15. Clinical Considerations Many factors impact effectiveness of exercise program: • Medications • Physical health • Age • Program design All can impact ability to participate and physical response to training stimulus.

16. Morphology and Physiology of Muscle Performance Improving muscle performance often translates into improvements in functioning by the patient.

17. Dosage Can be Altered in a Variety of Ways: • Increasing intensity/load • Changing relationship to gravity • Increasing lever arm length • Increasing sets/repetitions • Decreasing rest interval • Increasing frequency Intensity, duration, frequency are related and considered “training volume”. All must be considered when designing a program. Resistive exercise must progress functional activity to transition intervention at impairment level to a functional situation

18. Sequence • Generally – Multijoint exercises for strength and power gains. • For patient’s – First – Specific isolated training for impaired muscle performance. • Isometric to multijoint, slow to fast speeds, For General Strength: • Large muscle groups before small • Multijoint before single-joint “activities” • When training individual muscle groups, perform higher intensity exercises before lower intensity exercises

19. More Factors Affecting Muscle Performance • Program Design – looking at the overall training session. • 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). • Muscle Soreness – Some activity is still advised!

20. 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.

21. Puberty • Body composition changes to 27–40% of body mass (Boys). • Onset of puberty, strength of boys and girls diverges remarkably. • General strength training is recommended. • Avoid heavy loads (epiphyses remain vulnerable to injury).

22. 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.

23. Middle Age • Decrement of strength must be differentiated. • Training for as little as 2 hours per week can positively influence strength. • Small amount of training increases the difference b/t active and inactive persons. • Leisure time activities account more for existing strength than professional demands

24. Advanced Age • Possible to reverse muscular weakness in old age. • Resistive exercise should be directed toward muscles susceptible to atrophic changes. (e.g. deep neck flexors, scapular stabilizers, abdominal muscles, pelvic floor muscles, gluteal muscles, and quadriceps) • Training considerations should include power and strength.

25. More Factors Affecting Muscle Performance • Cognitive aspects of performance (e.g.visualization) • Effects of alcohol • Effects of corticosteroids

26. Causes of Decreased Muscle Performance • Neurologic pathology • Muscle strain • Disuse and conditioning • Length-associated changes

27. Physiologic Adaptations to Resistive Training • Improvement in muscle performance • Positive effects on cardiovascular system, connective tissue, and bone Improved Functioning

28. 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

29. Endurance Muscle’s response to endurance training different from its strength or power training. Muscles trained for endurance: • Demonstrate cells with increased mitochondrial size, number, and enzymatic activity • Delays onset of muscular fatigue. • Demonstrate increased local fuel storage (up to 2-fold). • Increase fatty acid use and decreases use of glycogen as fuel. • Allows more exercise before fatigue. • Improves oxygen delivery system by increasing the local capillary network, producing more capillaries per muscle

30. 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 AND MORE

31. Activities to Increase Muscle Performance • Isometric Exercise (strength base for dynamic exercise) • Dynamic Exercise (weight machine exercise, free-weight exercise, plyometric exercise) • Isokinetic Exercise (provides maximum resistance throughout entire ROM)

32. Methods of Resistance Training

33. 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.

34. 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.

35. 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).

36. Therapeutic Exercise Intervention for Impaired Muscle PerformanceProgram Initiation • What muscle or muscle group(s) need training? • What type of training is required at this stage? • Should muscle be isolated or worked as a synergist? • What activity will best accomplish this goal? • What is their current performance status? • Based on tests, what resistance will they tolerate and for how many repetitions? • What is the best mode to perform the exercise

37. Program Progression • Exercises can be progressed many ways (e.g. increasing exercise intensity, to changing complexity of exercise. • Goal is to narrow/eliminate gap b/t the patient’s current status and desired functional status.

38. Therapeutic Exercise Intervention for Prevention, Health Promotion and Wellness • Dosage for Strength Training • Dosage for Endurance Training • Dosage for Power Training • Dosage for Advanced/Elite Athlete • Plyometrics Similar training (and safety) strategies employed for athletes as for patients. Focus of sport or state of wellness tends to dictate level of exercise intensity and difficulty.

39. 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. • Dynamic action is the preferred term over isotonic.

40. Summary (cont.) • Dynamic actions can be further divided into concentric and eccentric actions. • The sliding filament theory describes the events that occur during muscle contraction. Force gradation occurs by rate coding and size principles. • Basic muscle fiber types are slow oxidative, fast glycolytic, and fast oxidative glycolytic. • Force gradation occurs by rate coding and the size principle.

41. 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.

42. Summary (cont.) • 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. • Dynamic exercise may include free weights, resistive bands, pulleys, weight machines, or body weight.

43. Summary (cont.) • Dosage of exercise depends on the goal. • Precautions and contraindications must be known to ensure safety.