Adaptations to Resistance Training PDF

Adaptations to Resistance Training CHAPTER 11 Overview • Resistance training and gains in muscular fitness • Mechanisms of gains in muscle strength • Interaction between resistance training and diet • Resistance training for special populations Resistance Training: Introduction • Substantial str...

Adaptations to Resistance Training CHAPTER 11 Overview • Resistance training and gains in muscular fitness • Mechanisms of gains in muscle strength • Interaction between resistance training and diet • Resistance training for special populations Resistance Training: Introduction • Substantial strength gains via neuromuscular changes • Important for overall fitness and health • Critical for athletic training programs Resistance Training: Gains in Muscular Fitness • After 3 to 6 months of resistance training – 25% to 100% strength gain – Better force production – Ability to produce true maximal movement • Similar strength gains as percentage of initial strength – But greater absolute gains for young men than for young women, older men, or children – Due to incredible muscle plasticity Mechanisms of Muscle Strength Gain • Hypertrophy versus atrophy – muscle size  muscle strength – muscle size  muscle strength – But association more complex than that • Sources of strength gains – muscle size – Altered neural control Figure 11.1a Figure 11.1b Figure 11.1c Mechanisms of Muscle Strength Gain: Neural Control • Strength gain cannot occur without neural adaptations via plasticity. – Strength gain can occur without hypertrophy. – Strength is a property of the motor system, not just of muscle. • Essential elements include motor unit recruitment, stimulation frequency, and other neural factors. Mechanisms of Muscle Strength Gain: Motor Unit Recruitment (1 of 2) • Motor units normally recruited asynchronously • Synchronous recruitment  strength gains – Facilitates contraction. – May produce more forceful contraction. – Improves rate of force development. – Improves capability to exert steady forces. • Resistance training  synchronous recruitment (continued) Mechanisms of Muscle Strength Gain: Motor Unit Recruitment (2 of 2) • Strength gains may also result from greater motor unit recruitment. – – – neural drive during maximal contraction frequency of neural discharge (rate coding) inhibitory impulses • Likely that a combination of improved motor unit synchronization and motor unit recruitment leads to strength gains. Mechanisms of Muscle Strength Gain: Motor Unit Rate Coding • Limited evidence suggests that rate coding increases with resistance training, especially rapid-movement, ballistic-type training. Mechanisms of Muscle Strength Gain: Autogenic Inhibition • Normal intrinsic inhibitory mechanisms – Example: Golgi tendon organs. – Inhibit muscle contraction if tendon tension too high. – Prevent damage to bones and tendons. • Inhibitory impulses  by training – Muscle can generate more force. – May also explain superhuman feats of strength. Mechanisms of Muscle Strength Gain: Other Neural Factors • Coactivation of agonists, antagonists – Normally antagonists oppose agonist force. – Reduced coactivation may  strength gain. • Morphology of neuromuscular junction Mechanisms of Muscle Strength Gain: Muscle Hypertrophy • Hypertrophy: increase in muscle size • Transient hypertrophy (after exercise bout) – Due to edema formation from plasma fluid – Gone within hours • Chronic hypertrophy (long term) – Structural change in muscle – Fiber hypertrophy, fiber hyperplasia, or both Figure 11.2a Figure 11.2b Mechanisms of Muscle Strength Gain: Chronic Muscle Hypertrophy • Maximized by high-velocity eccentric training, which disrupts sarcomere Z-lines (protein remodeling). • Concentric training may limit muscle hypertrophy, strength gains. • Stimulated by intensities as low as 30% 1RM and as high as 90%. • Caused by both high-rep (low-load) and lowrep (high-load) training. Mechanisms of Muscle Strength Gain: Fiber Hypertrophy • • • • • More myofibrils More actin, myosin filaments More sarcoplasm More connective tissue Resistance training  protein synthesis – Muscle protein content always changing – During exercise: synthesis , degradation – After exercise: synthesis , degradation Mechanisms of Muscle Strength Gain: Hormones and Hypertrophy • Fiber hypertrophy facilitated by testosterone – Natural anabolic steroid hormone – Synthetic anabolic steroids  large increases in muscle mass • Growth hormone (GH) • Insulin-like growth factor 1 (IGF-1) • Elevated postexercise levels not required for anabolism and strength Mechanisms of Muscle Strength Gain: Fiber Hyperplasia (1 of 3) • Cats – Intense strength training produces fiber splitting. – Each half grows to size of parent fiber. • Chickens, mice, rats – Intense strength training produces only fiber hypertrophy. – But difference may be due to training regimen. (continued) Figure 11.3 Mechanisms of Muscle Strength Gain: Fiber Hyperplasia (2 of 3) • Humans – Most hypertrophy is due to fiber hypertrophy. – Fiber hyperplasia also contributes. – Fiber hypertrophy versus fiber hyperplasia may depend on resistance training intensity or load. – Higher intensity causes (type II) fiber hypertrophy. • Fiber hyperplasia may occur only in certain individuals under certain conditions. (continued) Mechanisms of Muscle Strength Gain: Fiber Hyperplasia (3 of 3) • Can occur through fiber splitting. • Also occurs through satellite cells. – Myogenic stem cells involved in skeletal muscle regeneration – Activated by stretch, injury – After activation: proliferate, migrate, fuse Figure 11.4 Animation 11.4 For audio description use this link: https://players.brightcove.net/901973548001/kplGlX8REA_default/index.html?videoId=6263541 048001 Mechanisms of Muscle Strength Gain: Neural Activation and Hypertrophy • Short-term in muscle strength • Long-term in muscle strength – Substantial in 1RM – Due to voluntary neural activation – Neural factors critical in first 8 to 10 weeks – Associated with significant fiber hypertrophy – Net protein synthesis requiring time to occur – Hypertrophy major factor after first 10 weeks Mechanisms of Muscle Strength Gain: Atrophy and Inactivity • Reduction or cessation of activity  major change in muscle structure and function • Limb immobilization studies • Detraining studies Mechanisms of Muscle Strength Gain: Immobilization • Major changes after 6 h – Lack of muscle use  reduced protein synthesis. – Initiates process of muscle atrophy. • First week: strength loss of 3%-4% per day – – size (atrophy) neuromuscular activity • (Reversible) effects on type I and II fibers – Cross-sectional area , cell contents degenerate. – Type I is affected more than type II. Mechanisms of Muscle Strength Gain: Detraining • Leads to in 1RM. – Lost strength can be regained (~6 weeks). – New 1RM matches or exceeds old 1RM. • Once training goal met, maintenance resistance program prevents detraining. – Maintain strength and 1RM. – Reduce training frequency. Figure 11.6 Mechanisms of Muscle Strength Gain: Fiber Type Alterations (1 of 2) • Training regimen may not outright change fiber type, but . . . – Type II fibers more oxidative with aerobic training – Type I fibers more anaerobic with anaerobic training • Fiber type conversion is possible under certain conditions. – Cross-innervation – Chronic low-frequency stimulation – High-intensity treadmill or resistance training (continued) Mechanisms of Muscle Strength Gain: Fiber Type Alterations (2 of 2) • Type IIx  type IIa transition common • 20-week heavy resistance training program: – Static strength, cross-sectional area – Percentage type IIx , percentage type IIa • Other studies: type I  type IIa with highintensity resistance work + short-interval speed work Interaction Between Resistance Training and Diet • Resistance training increases protein synthesis. • Consume 20 to 25 g protein after resistance exercise for muscle growth. • Consume 1.6 to 1.7 g protein per kg body weight per day to increase muscle mass. • Small doses (20 g) every 2 to 3 hours are recommended for protein synthesis. • Larger doses (20-25 g) recommended immediately after resistance training. Molecular Mechanisms of Increased Protein Synthesis • Repeated muscle stretch → ↑ IGF-1 • ↑ IGF-1 → ↑ mTOR – Integrates input from insulin, growth factors, amino acids. – Dictates transcription of mRNA. – Synthesizes ribosomes. • Stimulated by insulin • Translation – Amino acids converted into protein via mRNA. Figure 11.7 Figure 11.8 Animation 11.8 For audio description use this link: https://players.brightcove.net/901973548001/kplGlX8REA_default/index.html?videoId=6259867 027001 Video 11.1 Resistance Training for Special Populations: Age • Children and adolescents – Myth: Resistance training is unsafe due to growth plate, hormonal changes. – Truth: It is safe with proper safeguards. – Children can gain both strength and muscle mass. • Elderly persons – Helps restore age-related loss of muscle mass. – Improves quality of life and health. – Helps prevent falls. Strength Training in Older Adults • Increases in strength dependent primarily on neural adaptations – No difference across sex or race • Same response as in younger but blunted – Decreased mTOR signaling response – Smaller increases in myofibrillar protein and muscle size – 25-50 g protein necessary to stimulate muscle protein synthesis Resistance Training for Sport • Training is not worth it beyond the basic strength, power, and endurance needs of the chosen sport. • Training costs valuable time. • Training results should be tested with sportspecific performance metrics.