Interventions for Physiologic Impairments During Rehabilitation

IMPAIRED MUSCLE PERFORMANCE - Study Notes

1. Definitions and Key Concepts

• Strength - the ability to produce force (torque) against resistance
• Power - the rate of force production (force x velocity)
• Endurance - the ability to sustain repeated contractions over time

2. Types of Muscle Contraction Used in Rehabilitation

3. Isometric Exercise

• Foundational exercise - often precedes dynamic training
• Used to pre-tension muscles before eccentric contractions
• Preferred when joint motion is painful or contraindicated (e.g., post-op, unstable joint)
• Essential to prevent strength loss during immobilization
• Combined with dynamic exercise to address a "sticking point" in the ROM
• Muscle re-education after nerve injury
• Core stabilization programs

4. Resistance Training Principles

The Overload Principle (foundational)

Dose-Response for Strength Gains

• Strength increases approximately 30% in the first 6-8 weeks of a resistive training program in previously untrained individuals
• Gains plateau after ~10 weeks at a given loading stimulus - load must be progressively increased (progressive overload)
• In elderly sedentary individuals, where severe atrophy has occurred, strength gains exceeding 100% are achievable

ACSM Sequencing Recommendations (for general population)

• Large muscle groups before small
• Multi-joint exercises before single-joint exercises
• Alternate upper body and lower body when training all major muscle groups in one session
• When training upper/lower on separate days, order within each session follows the same large-before-small principle

Rehabilitation Sequencing (injured patient)

• Single-joint (isolated) exercises first, before fatigue sets in - this is reversed from the general population recommendation
• Follow isolated exercises with multi-joint functional movement patterns
• Unstacking exercises (alternating between different muscle groups) is preferred in early rehabilitation to allow active rest and prevent overwork
• As rehabilitation progresses, stacking (sequential exercises for the same muscle group) can be introduced

5. Muscle Hypertrophy

1. Increased number of myofibrils proportionate to hypertrophy
2. Up to 120% increase in mitochondrial enzymes
3. 60-80% increase in phosphagen metabolic system components (ATP, phosphocreatine)
4. Up to 50% increase in stored glycogen
5. 75-100% increase in stored triglyceride (fat)
6. Overall increase in maximum oxidation rate and efficiency of the oxidative metabolic system by ~45%

• Guyton & Hall Textbook of Medical Physiology

6. Fast-Twitch vs. Slow-Twitch Fiber Considerations

7. Eccentric Training

• A common mechanism of muscle strain injury (therefore must be trained to prevent injury)
• Associated with greater force production per unit of cross-sectional area than concentric
• The basis for tendinopathy protocols (e.g., Alfredson protocol for Achilles tendinopathy)
• Effective at producing hypertrophy, including in weakened/atrophied muscle

• Dynamic resistive exercises with strong eccentric loading
• Flexibility exercises
• Appropriate warm-up before activity
• Attention to fatigue levels

8. Positional Strengthening and Length-Tension Considerations

• Positionally weak muscle (e.g., chronically lengthened/inhibited): strengthen in the shortened range
• Globally weak muscle: strengthen dynamically throughout the full range
• The goal is restoring the muscle's ability to generate force at the appropriate point in the ROM for function - Brody's Therapeutic Exercise (Lippincott)

9. Muscle Imbalance and Therapeutic Targeting

1. Disuse atrophy - rapid losses begin within 24-48 hours of immobilization; predominantly affects Type II fibers initially
2. Neurologic inhibition - pain, effusion, and swelling reflexively inhibit local muscles (e.g., quadriceps inhibition with knee effusion)
3. Overuse/muscle imbalance - overactive muscles become shortened and inhibit their antagonists; underused muscles weaken
4. Inflammatory myopathy - acquired metabolic disturbance contributes directly to impaired muscle performance via immune-mediated fiber damage

• Identify and strengthen underused muscles to reduce overuse demands on susceptible muscles
• Restore muscle balance around joints before advancing to high-load functional training

10. Modalities and Adjuncts for Muscle Performance

11. Stages of Motor Control (Framework for Exercise Progression)

1. Mobility - achieve basic ROM and initiate muscle activation (isometric, AROM)
2. Stability - co-contraction to stabilize the joint; static weight-bearing
3. Controlled mobility - proximal movement on a fixed distal segment; dynamic stability
4. Skill - high-speed, coordinated, task-specific movements

12. Rehabilitation vs. Fitness Programming

• Sustain and build on rehabilitation gains
• Prevent injury recurrence through continued eccentric loading, flexibility, and appropriate progression

13. Special Populations

• Elderly/sarcopenic patients: Significant muscle atrophy from inactivity may respond with >100% strength gains from resistance training. Resistance exercise is the primary intervention for sarcopenia.
• Neurologic patients (stroke, SCI): Progressive resistance exercises, virtual reality, aquatic exercise, elastic bands - no evidence that strengthening induces spasticity. NMES and FES are adjuncts.
• Inflammatory/rheumatic disease: Exercise reduces pro-inflammatory cytokines (IL-6, TNF-α), promotes IL-10; aerobic and resistance exercise are both effective and safe during remission.
• Post-COVID/critical illness: Patients with muscle weakness from prolonged hospitalization require rehabilitation, though optimal protocols are still being defined.

14. Quick Reference: Training Variables

Summary

• Early phase: Isometrics, NMES, neuromuscular re-education, aquatic exercise, low-load isotonics
• Middle phase: Progressive resistance exercise, eccentric loading introduced, functional movements, muscle balance restoration
• Late phase: High-load/power training, sport-specific or task-specific movements, eccentric emphasis, prevention program
• Transition: Fitness program with ACSM-based progressive overload, eccentric components, and continued attention to flexibility and fatigue management

Interventions for Physiologic Impairments During Rehabilitation

IMPAIRED ENDURANCE - Exam Notes

LEVEL 1 - THE BASICS (Start Here)

What is Endurance?

• Cardiorespiratory (aerobic) endurance - the ability of the heart, lungs, and circulation to deliver oxygen to working muscles during prolonged activity
• Local muscular endurance - the ability of a specific muscle group to perform repeated contractions without fatigue

What is Impaired Endurance?

• Prolonged bed rest / immobilization
• Cardiac or respiratory disease
• Post-surgical deconditioning
• Neurologic or musculoskeletal conditions
• Inflammatory disease (e.g., rheumatoid arthritis, myopathies)

LEVEL 2 - KEY CONCEPT: VO₂max

• It represents the maximum rate at which the body can consume oxygen during maximal exercise
• Normal: ~38 mL/kg/min in active healthy men; ~29 mL/kg/min in active healthy women
• Exercise training increases VO₂max - this is the primary goal of endurance rehabilitation
• A 1-MET increase in exercise capacity after cardiac rehabilitation = 13% reduction in mortality risk; in low-fitness patients, this rises to 30% reduction
• Fuster and Hurst's The Heart, 15th Ed.

MET Levels - Simple Reference

• Goldman-Cecil Medicine

LEVEL 3 - THE FITT-VP PRINCIPLE (Exercise Prescription Framework)

LEVEL 4 - MODES OF AEROBIC EXERCISE

LEVEL 5 - TWO MAIN TRAINING APPROACHES

A. Continuous Endurance Training (CET)

• Patient exercises at a constant, moderate intensity for the entire session
• Example: Walk at 3.4 mph for 30 minutes
• Best for: Most rehabilitation populations; easy to teach and monitor
• Builds: Aerobic base, cardiovascular efficiency, walking endurance

B. Interval Training

• Alternating periods of high-intensity exercise with rest or low-intensity activity
• Work:Relief ratios vary by goal:

• A longer work interval (≥3 minutes) trains the aerobic system - requires shorter recovery
• A shorter, high-intensity bout trains the phosphagen/anaerobic system - requires much longer recovery
• Relief interval can be passive (rest) or active (light activity, stretching)
• Brody's Therapeutic Exercise (Lippincott)

LEVEL 6 - HIGH-INTENSITY INTERVAL TRAINING (HIIT)

Why HIIT Matters in Rehabilitation:

• More effective than moderate-intensity continuous training for improving cardiorespiratory fitness
• Completely eliminates non-responders to exercise training when performed at high volume + high intensity (a key finding: low volume/low intensity exercise still leaves ~40% non-responders)
• Safe in patients with cardiovascular disease when properly supervised
• In COPD: periods of high-intensity exercise (20-30 sec) alternated with low-intensity or rest (30-40 sec) produces comparable gains to continuous training - ideal for patients who cannot sustain continuous exertion
• In cardiac rehabilitation: HIIT produces greater improvement in VO₂peak than moderate continuous exercise
• Fuster and Hurst's The Heart, 15th Ed.; Murray & Nadel's Respiratory Medicine

HIIT Protocol Example:

4 x 4 minutes at 85-95% max HR, with 3-minute active recovery at 50-70% max HR between bouts (the "Norwegian" HIIT protocol used in cardiac rehab)

LEVEL 7 - MONITORING EXERCISE INTENSITY

1. Heart Rate Methods

• Target Heart Rate (THR) = most common clinical method
• Karvonen Formula: THR = Resting HR + (Intensity% × Heart Rate Reserve)
  • HRR = Max HR - Resting HR
• Max HR estimate: 220 - age (simple) OR 208 - (0.7 × age) (more accurate)

2. Rating of Perceived Exertion (RPE) - Borg Scale

• RPE 12-16 = the usual target zone for rehabilitation endurance training
• RPE may be affected by psychological state, medications (especially beta-blockers), and unfamiliarity with exercise equipment

3. METs

• Prescribe activity within a target MET range based on the patient's baseline functional capacity (e.g., start at 3-4 METs if patient tolerates 5 METs on initial testing)

4. Talk Test

• Simple: Patient should be able to speak in short sentences but not carry on a full conversation = appropriate moderate intensity

5. 6-Minute Walk Test (6MWT)

• Safe, low-cost field test used to both assess baseline and prescribe exercise intensity
• Target HR at end of 6MWT is used to set training heart rate in cardiac and pulmonary rehab
• Murray & Nadel's Respiratory Medicine

LEVEL 8 - PHYSIOLOGIC ADAPTATIONS TO ENDURANCE TRAINING

• Increased stroke volume (cardiac hypertrophy - "athlete's heart")
• Decreased resting heart rate (vagal dominance)
• Increased cardiac output during maximal exercise
• Improved coronary blood flow

• Increased mitochondrial density and oxidative enzyme activity (+45% in aerobic metabolic system efficiency)
• Increased capillary density in skeletal muscle
• Improved oxygen extraction (wider arteriovenous O₂ difference)
• Shift toward fat as fuel (sparing glycogen)
• Increased stored glycogen and triglycerides in muscle

• Guyton & Hall Medical Physiology; Medical Physiology (Boron & Boulpaep)

LEVEL 9 - SPECIAL CONSIDERATIONS IN REHABILITATION

COPD / Pulmonary Rehabilitation

• Endurance training is the cornerstone of pulmonary rehabilitation
• Target intensity: 60-80% of maximal workload for greatest gains
• Low-intensity exercise (<50% max) still provides benefit in severely limited patients
• Walking-based training improves walking endurance more than cycling
• Cycling preferred when there is significant oxygen desaturation with walking
• One-legged cycling (single-leg): trains smaller muscle group → allows higher intensity, less ventilatory demand → greater VO₂ gains
• Interval training is the preferred alternative when patients cannot tolerate continuous exercise
• Optimize bronchodilators before exercise to allow higher training intensities
• Supplemental O₂ during exercise for hypoxemic patients improves endurance and allows higher training loads
• Murray & Nadel's Textbook of Respiratory Medicine

Cardiac Rehabilitation

• Each 1-MET increase = 13% reduction in mortality; up to 30% in low-fitness patients
• High volume + high intensity training eliminates exercise non-responders
• HIIT is more effective than moderate continuous training for improving VO₂peak
• Heart failure patients benefit from gradual volume increase + aerobic + resistance combination
• Fuster and Hurst's The Heart

Musculoskeletal / Arthritis / Post-Surgical

• Aquatic exercise in early stages when weight-bearing is limited
• Transition to land-based exercise as pain and function improve (land exercise improves aerobic capacity and pain more than aquatic long-term)
• Combine aerobic + resistance training for optimal outcomes
• Goldman-Cecil Medicine

Inflammatory Myopathies (PM/DM)

• Endurance exercise improves cycling time and aerobic capacity
• Reverses tissue hypoxia caused by microvascular involvement
• Rheumatology 2-Volume Set (Elsevier)

LEVEL 10 - CIRCUIT TRAINING (Advanced Design)

• Stations rotate through muscle groups, allowing active rest
• Develops both local muscular endurance and cardiorespiratory endurance simultaneously
• Rest interval between stations: ~30 seconds (for muscle endurance goal)
• Highly time-efficient; good for late-stage rehabilitation and transition to wellness

• Prevent plateaus
• Maintain patient interest
• Provide a balanced program
• Brody's Therapeutic Exercise (Lippincott)

QUICK SUMMARY TABLE - Simple to Complex Progression

EXAM QUICK POINTS TO REMEMBER

1. VO₂max = gold standard of aerobic capacity; training increases it
2. FITT-VP: Frequency, Intensity, Time, Type, Volume, Progression
3. Increase duration before intensity when progressing
4. HIIT > moderate continuous training for VO₂max improvement; safe in CVD with supervision
5. Interval training is preferred for patients who cannot sustain continuous exertion (COPD, severe deconditioning)
6. Aerobic work interval ≥3 minutes = trains aerobic system; short, all-out bursts = phosphagen system
7. Walking > cycling for walking endurance; cycling > walking for minimizing O₂ desaturation in COPD
8. 1-MET gain = 13% mortality reduction in cardiac rehab patients
9. RPE 12-16 (Borg scale) = appropriate rehabilitation exercise intensity
10. Non-responders to exercise training are eliminated by high volume + high intensity training