Resistance Training Lecture: Biomechanics and Physiology PDF

3.1 Foundations of Resistance Training This lecture covers the biomechanics and physiology of resistance training, focusing on clinical application. It explores energy systems—phosphagen (short, high-intensity), fast glycolysis (moderate duration), and oxidative (long, low-intensity)—and their role...

3.1 Foundations of Resistance Training This lecture covers the biomechanics and physiology of resistance training, focusing on clinical application. It explores energy systems—phosphagen (short, high-intensity), fast glycolysis (moderate duration), and oxidative (long, low-intensity)—and their roles in exercise and recovery. Torque mechanics are emphasized, highlighting external torque (resistance from gravity and lever arms) and internal torque (muscle force and anatomy). Exercise prescription involves manipulating variables like load, lever arm length, and contraction type (concentric, isometric, eccentric) based on rehabilitation goals and functional demands. The session underscores the importance of understanding biomechanics, energy systems, and torque for optimizing outcomes in physical therapy. Key Points 1.​ Energy Systems in Resistance Training ○​ Phosphagen System (High-Intensity, Short-Duration) ​ Used for max effort activities (e.g., max-height box jumps). ​ Duration: Up to 5-6 seconds. ​ Rest: Significant rest required to replenish. ○​ Fast Glycolysis (High-Intensity, Moderate-Duration) ​ Duration: 6 seconds to 2 minutes. ​ Produces lactic acid when oxygen supply is insufficient. ​ Rest: Adequate recovery time required to restore glycogen levels. ○​ Oxidative System (Low-Intensity, Long-Duration) ​ Duration: Over 2-3 minutes. ​ Unlimited capacity, fueled by carbohydrates and fats. ​ Lower intensity allows continuous energy production. 2.​ Torque Mechanics ○​ External Torque ​ Resistance torque = Gravity x Weight x Lever Arm Distance. ​ Examples of manipulation: ​ Increase weight or move it further from the joint to increase torque. ​ Use cuffs or modify equipment positions to reduce torque. ○​ Internal Torque ​ Created by muscles via force production and lever arm of muscle insertion. ​ Anatomy dictates the lever arm; exercise increases muscle force capacity. ○​ Practical Examples ​ Bicep curls: Torque varies across range of motion due to changes in lever arms. ​ Planks: Resistance force is gravity, but lever arm modifications (e.g., wall plank vs. full plank) alter perceived difficulty. 3.​ Factors Influencing Torque  ○​ External Torque ​ Influenced by the type of resistance (e.g., free weights, cables, resistance bands). ​ Resistance bands: Force increases as the band stretches. ○​ Internal Torque ​ Determined by anatomy (insertion points, angles). ​ Muscle force production influenced by: ​ Length-tension relationships. ​ Muscle cross-sectional area (hypertrophy increases torque). ​ Contraction velocity (fast vs. slow). ​ Joint angular velocity (type of contraction). 4.​ Types of Muscle Contractions ○​ Concentric ​ Muscle shortens while exerting force (e.g., lifting in a bicep curl). ○​ Isometric ​ No joint movement; muscle contracts to hold a position. ​ Used in early rehab (e.g., multi-angle stabilization, pain reduction). ○​ Eccentric ​ Muscle lengthens while controlling force (e.g., sitting down into a chair). ​ Key for: ​ Tendon rehab (stimulates tendon growth). ​ Functional activities (e.g., walking downhill). ​ High-load eccentric exercises cause more microdamage (positive for adaptation but needs careful use in rehab). 5.​ Clinical Application of Resistance Training ○​ Understand energy systems and torque mechanics for effective exercise prescription. ○​ Choose contraction type (concentric, isometric, eccentric) based on rehab stage and patient goals. ○​ Modify variables (e.g., load, lever arm, equipment) to match functional and therapeutic needs. ○​ Pay attention to biomechanics (e.g., lever arms, muscle angles) for specific exercises to optimize outcomes. 6.​ Key Takeaways ○​ Resistance training revolves around energy systems, torque mechanics, and muscle function. ○​ Torque and contraction type play pivotal roles in exercise prescription. ○​ Clinical application requires tailoring exercises to individual needs based on biomechanical and physiological principles. 3.2 Resistance Exercise Dosing This session focuses on applying physiological processes and biomechanical principles to exercise prescription and decision-making. The approach begins with identifying the patient's primary movement problem through observation and assessing factors like pain, swelling, range of motion, muscle strength, coordination, or motor control. Exercise prescription is tailored to specific goals, such as loading injured tissues, managing pain, improving strength, endurance, flexibility, or motor control. Key guidelines include starting with low loads and progressively increasing intensity based on goals (e.g., strength, power, hypertrophy, or endurance), while considering appropriate dosing, reps, and rest intervals. Early rehab emphasizes isometrics, active range of motion, and muscle activation to address swelling, joint mobility, and initial muscle engagement. For motor control and functional movement improvements, high reps and progressive complexity are essential. Ultimately, every exercise must have a clear purpose aligned with the patient’s needs and goals. Key Points 1.​ Key Factors to Address ○​ Injured Tissue: Start with low loads and progressively increase. ○​ Pain/Swelling: Use active or passive range of motion. ○​ Muscle Function/Performance: Progressively load muscles to improve strength, power, or endurance. ○​ Range of Motion: Employ joint mobilization and stretching. ○​ Motor Control: Train balance, coordination, and agility through specific, repetitive exercises. ○​ Functional Movements: Start simple and increase complexity to address strength, range of motion, and movement patterns. 2.​ Key Components of Muscle Performance ○​ Strength: ​ Measure of force/torque a muscle can produce (e.g., heavy lifting). ​ Typically involves high load and 2-6 repetitions. ​ Requires adequate rest for energy system recovery. ○​ Power: ​ Force generation with speed (e.g., jumping, sprinting). ​ Includes single or multiple effort events (e.g., max effort jumps, power cleans). ​ Requires high-intensity training with long rest intervals. ○​ Hypertrophy: ​ Growth of muscle size after atrophy due to injury or disuse. ​ Focus on 6-12 reps with moderate loads. ​ Rest intervals are shorter than for strength or power training. ○​ Muscular Endurance: ​ Ability to sustain force over time (e.g., planks, wall sits).  ​ High repetition range (12+ reps) with minimal rest. 3.​ Dosing and Exercise Setup ○​ Repetition Ranges: ​ Strength: 2-6 reps. ​ Hypertrophy: 7-12 reps. ​ Endurance: 12+ reps. ○​ Estimating Load: ​ Adjust weight based on desired reps (e.g., ballpark starting weight, refine based on performance). ​ Use Rate of Perceived Exertion (RPE) to assess difficulty. 4.​ Energy Systems and Rest Intervals ○​ Strength and Power: Phosphagen and fast glycolysis systems, requiring longer rest periods. ○​ Hypertrophy: Mix of fast glycolysis and aerobic metabolism, allowing moderate rest periods. ○​ Endurance: Primarily aerobic metabolism, with shorter rest periods. 5.​ Early Stages of Rehabilitation ○​ Isometric Exercises (Muscle Setting): ​ Low-load contractions (e.g., tighten and hold for 6 seconds, repeat 10 times). ​ Used to activate muscles and reduce swelling. ○​ Active Range of Motion (AROM): ​ Movement without added load (e.g., shoulder flexion for 30 seconds). ​ Focuses on joint mobility and edema reduction. ○​ Early Muscle Activation: ​ Transition phase with low loads and fewer sets. ​ Prepares muscles for more traditional exercises. ○​ Motor Control Training: ​ High repetitions to develop neuromuscular learning (e.g., balance and coordination tasks). 6.​ Practical Tools ○​ NSCA Guidelines: Use repetition maximums (e.g., 1RM) to estimate load and reps. ○​ Clinical Adjustments: Adapt training intensity and volume based on patient ability and clinical goals. ○​ Progression: Gradually refine exercise prescriptions based on patient feedback and observed outcomes. 3.3 Modifying and Progressing Resistance Exercise This lecture emphasizes adapting and progressing exercises based on patient needs, fitness levels, and goals, using principles like SAID (Specific Adaptation to Imposed Demands). Initial dosing for deconditioned patients may involve one set of 8–12 reps, with progression adjusted for endurance (higher reps) or strength (lower reps, higher load). Key methods of adaptation include modifying external torque (e.g., increasing weight), lever arms (e.g., plank progression), resistance modes (e.g., bands, free weights), base of support (e.g., wider stance or unstable surfaces), and movement speed or complexity (e.g., single-joint to multi-joint). Functional progression transitions patients from isolated exercises to real-world or sport-specific movements, advancing from controlled environments to open, unpredictable settings. Tailoring exercise plans to mirror patients' goals ensures effective rehabilitation and long-term success. Key Points 1.​ Dosing and Progression ○​ Initial Dosing: ​ For deconditioned patients (e.g., post-bed rest): 1 set of 8–12 reps (hypertrophy range) suffices. ​ For experienced individuals or progressing patients: adjust dosing. ○​ Options for Progression: ​ Endurance: Increase reps (e.g., 15–20). ​ Strength: Decrease reps (e.g., 6–8) and increase load. ​ Introduce periodization for advanced patients to ensure continuous adaptation. 2.​ Exercise Specificity ○​ Adapt exercises to mirror functional or sport-specific movements. ​ Example: Train hamstrings with high-load, high-velocity eccentric contractions for sprinting. ○​ Transition from isolated exercises to functional, multi-joint activities over time. ○​ Match exercise complexity and movement patterns to patient goals (e.g., running, gardening). 3.​ Methods of Adaptation ○​ External Torque: ​ Increase weight/load (e.g., add 10 lbs to a squat). ○​ Lever Arm Adjustment: ​ Example: Progress planks (wall → table → knee → full). ○​ Mode of Resistance: ​ Examples: 1.​ Resistance bands: Increase resistance at the end range. 2.​ Free weights: Constant load. 3.​ Cables: Variable load based on lever arms. ○​ Base of Support:  ​ Widen for stability; narrow or shift to single-leg for increased challenge. ​ Use unstable surfaces (e.g., foam pad, wobble board) to increase difficulty. ○​ Speed of Movement: ​ Tailor velocity to activity goals: 1.​ Moderate speed for early rehab. 2.​ High speed for sport-specific demands (e.g., sprinting). ​ Adjust joint angular velocity (isometric, concentric, eccentric). ○​ Complexity of Movement: ​ Begin with single-joint, sagittal plane exercises. ​ Progress to multi-joint, multi-plane, and functional movements. 4.​ Functional and Environmental Progressions ○​ Isolation to Function: ​ Example: Move from leg press to step-ups or lunges. ○​ Simple to Complex Tasks: ​ Add multitasking (e.g., catching a ball during step-ups). ○​ Closed to Open Environments: ​ Start in a controlled clinic; progress to busier, unpredictable settings. ​ Example: ACL rehab → transition to soccer-field-like environments. 5.​ Key Takeaways 6.​ Exercise progression should be goal-oriented, specific to patient needs, and adaptable over time. 7.​ Consider biomechanics, load, stability, and functionality when progressing exercises. 8.​ Align interventions with real-world environments for optimal recovery and performance. 3.4 Adaptations and Clinical Relevance Resistance training induces both neural and muscular adaptations, with neural changes, such as improved recruitment of fast-twitch motor units, occurring within the first six weeks and contributing to early strength gains. Muscular adaptations, primarily hypertrophy, improve insulin sensitivity, glycogen storage, and overall muscle function, benefiting conditions like Type 2 diabetes and enhancing athletic performance. Resistance training also promotes bone density through high-strain, high-force activities and improves tendon and ligament strength via progressive loading. Cartilage health is maintained through appropriate loading and unloading, debunking myths that exercise causes arthritis. While resistance training acutely increases cardiac output and heart rate during exercise, it does not negatively affect aerobic capacity or cause long-term changes in resting heart rate or blood pressure, making it safe for individuals with hypertension. Overall, resistance training offers widespread benefits for strength, health, and injury prevention across various tissues and systems. Key Points 1.​ Neural Adaptations ○​ Initial Changes: Neural adaptations occur early in resistance training, often visible within the first week. ○​ Increased Recruitment: The body recruits more fast-twitch motor units (Type 2 fibers) for power and speed. ○​ First 6 Weeks: Strength gains are primarily due to improved neural recruitment. ○​ Impact of Injury: Injuries and joint swelling inhibit neural recruitment. ​ E-stim Usage: Neuromuscular electrical stimulation (e-stim) can bypass inhibited pathways to stimulate muscles during early rehabilitation. ​ Transition: Once patients can recruit muscles independently, e-stim is no longer necessary. 2.​ Muscle Adaptations ○​ Hypertrophy: Increased number of contractile proteins within muscle fibers is the primary driver of muscle size gains. ○​ Insulin Sensitivity: Resistance training improves muscle sensitivity to insulin, helping manage Type 2 diabetes. ○​ Glycogen Storage: Increased glycogen storage in muscles benefits endurance and athletic performance. ​ Low-carb diets deplete glycogen stores, which impacts performance negatively for athletes. 3.​ Bone Adaptations ○​ Loading Benefits: High-strain, high-force activities (e.g., power training, plyometrics) improve bone density. ○​ Early Start: Bone loading should begin in adolescence and continue into adulthood to maintain bone density.  ○​ Osteopenia/Osteoporosis: Resistance and jump training can improve bone density in middle-aged and older adults. 4.​ Tendon and Ligament Adaptations ○​ Loading Response: Tendons and ligaments adapt by increasing collagen fibrils, cross-links, and diameter, improving strength and stability. ○​ Rehabilitation: Tendon injuries require progressive loading starting with isometric exercises and advancing to eccentric loading. ○​ Cartilage Adaptations ○​ Loading and Unloading: Compression and unloading improve nutrient diffusion and maintain cartilage health. ○​ Thickness Improvement: Regular, appropriately dosed exercise can increase cartilage thickness and protect joint surfaces. ○​ Arthritis Myth: Appropriate exercise throughout life helps prevent arthritis rather than causing it. 5.​ Cardiovascular System Adaptations ○​ Acute Responses: Resistance training increases cardiac output, heart rate, and blood flow to muscles during exercise. ​ Vasodilation in working muscles delivers nutrients and removes waste. ○​ Chronic Effects: ​ Resistance training does not negatively affect aerobic capacity (VO2 max or lactate threshold). ​ No long-term changes in resting heart rate or blood pressure (neither positive nor negative). ​ Safe for individuals with elevated blood pressure, though cardiovascular training is needed to lower it. 6.​ Additional Notes 7.​ Endurance Athletes: Resistance training enhances performance and does not impede endurance. 8.​ Runners: Running involves power (small jumps) and benefits from strength training.