Exercise Physiology: Ch. 10 (Adaptations to Resistance Training)

fiber hyperplasia vs fiber hypertrophy

-cats: intense strength training -> fiber splitting and each half grows to size of parent fiber -chicken, mice, rats: intense strength training -> only fiber hypertrophy -humans: fiber hypertrophy vs fiber hyperplasia may depend on resistance training/intensity load (higher intensity -> type II fiber hypertrophy)

gains in muscular fitness

after 3-6 months, 25-100% strength gain, learn to more effectively produce force; learn to produce true maximal movement; strength gains similar as a percent of initial strength (young men=greatest due to incredible muscle plasticity)

transient hypertrophy

after exercise bout; due to edema formation from plasma fluid; disappears within hours

long term increase in muscle strength

associated with significant fiber hypertrophy; net increase in protein synthesis takes time to occur; hypertrophy major factor after first 10 weeks

atrophy

decreased muscle size->decreased muscle strength; limb immobilization studies, bed rest studies, space flight, detraining studies

increased muscle strength via neural control

early gains in strength appear to be more influence by neural factors; strength gain cannot occur without neural adaptations via plasticity; motor unit recruitment, stimulation frequency, and other neural factors essential

resistance training for the elderly

helps restore age-related loss of muscle mass; improves quality of life and health; helps prevent falls

hypertrophy

increased muscle size->increased muscle strength; strength gain can occur without hypertrophy (via neural control)

muscle fiber hytrophy

increased size in existing muscle fibers; long-term strength increases are largely the result of muscle fiber hypertrophy via more myofibrils, more actin/myosin filaments, more sarcoplasm, and more connective tissue; testosterone facilitates (natural anabolic steroid hormone)

strength training in older adults

increases in strength dependent primarily on neural adaptations; same response as in younger, but blunted due to decreased mTOR signaling response and smaller increases in myofibrillar protein and muscle size; 25-50 g protein necessary to stimulate muscle protein synthesis

autogenic inhibition

inhibitory mechanisms in the neuromuscular system such as golgi tendon organs might be necessary to prevent the muscles from exerting more force than the bones/connective tissue can tolerate; training can decrease inhibitory impulses so the muscle can generate more force

detraining

leads to decreased 1RM; strength loss can be regained (~6 weeks); new 1RM matches or exceeds old; once training goal met, maintenance resistance program prevents detraining

motor unit rate coding

limited evidence suggests rate coding increases with resistance training, especially rapid movement, ballistic type training

chronic hypertrophy

long term; reflects actual structural change in muscle; fiber hypertrophy (increased size in existing muscle fibers), fiber hyperplasia (increase in the number of muscle fibers), or both; maximized by high-velocity eccentric training (concentric may limit)

immobillization

major changes after 6 hours: lack of muscle use leads to reduced rate of protein synthesis and initiates process of muscle atrophy first week: strength loss of 3-4% per day (decreased size and decreased neuromuscular activity) effects on type I and II fibers: cross sectional area decreases as cell contents degenerate (type I more affected)

muscle fiber hyperplasia

may only occur in certain individuals under certain conditions; can occur through fiber splitting; also occurs through satellite cells (involved in skeletal muscle regeneration and activated by stretch or injury); after activation, cells proliferate, migrate, fuse

resistance training for children and adolescents

myth: resistance training unsafe due to growth plate and hormonal changes truth: safe with proper safeguards, children can gain both strength and muscle mass

coactivation of agonists and antagonists

normally antagonists oppose agonist force; reduced coactivation may lead to strength gain

synchronous recruitment

normally motor units recruited asynchronously (not all engaged at same instant); synchronous recruitment-> strength gains: facilitates contraction, may produce more forceful contraction, improves rate of force development, increases capability to exert steady forces; resistance training -> synchronous recruitment

protein synthesis

resistance training increases protein synthesis; during exercise synthesis decreases and degradation increases, but after exercise synthesis increases and degradation decreases

strength gain mechanisms

result from increased muscle size and altered neural control

motor unit recruitment

strength gains result from greater motor unit recruitment: increases neural drive during maximal contraction, increases frequency of neural discharge (rate coding), decreases inhibitory impulses; likely that some combination of improved motor unit sychronization AND motor unit recruitment lead to strength gains

short term increase in muscle strength

substantial increase in 1RM; due to increased voluntary neural activation; neural factors critical in first 8-10 weeks

resistance training for sport

training beyond basic strength, power, and endurance needs of the sport not worth it; training costs valuable time; training results should be tested with sport-specific performance metric

resistance training and diet

training increases protein synthesis; 20-25 g of protein after resistance exercise for muscle growth; 1.6-1.7 g protein/ kg body weight/ day for increasing muscle mass; small doses (20 g) every 2-3 hours recommended for protein synthesis

fiber type alterations

type II fibers can become more oxidative with aerobic training and type I fibers can become more anaerobic with anaerobic training; fiber type conversion possible during: cross-innervation, chronic low-frequency stimulation, high-intensity treadmill or resistance training; type IIx -> type IIa transition common; type I -> type IIa with high intensity work and short interval speed work

resistance training

yields substantial strength gains via neuromuscular changes; important for overall fitness and health; critical for athletic training programs