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Flashcards in Skeletal muscle adaption to exercise Deck (10):

Fiber types 1

-Slow twitch fibers (red, type 1) and fast twitch fibers (white, type 2a and 2b)
-Everyone has 45-55% type 1 fibers, no gender differences exist but large variation from person to person
-The aMN innervating a muscle fiber dictates which fiber type the fiber will become
-Endurance athletes have mostly type 1 fibers, where as sprint athletes/weight lifters have mostly type 2


Fiber types 2

-Type 1 is slow to fatigue, much more myoglobin (aerobic)
-Type 2 is fast to fatigue, less myoglobin (2b: anaerobic, 2a: anaerobic and aerobic)
-Weight lifters/power athletes have enlargement of both fiber types
-Both endurance athletes and weight lifters demonstrate a conversion from 2b to 2a
-Larger muscle fibers and total muscle mass are the principle gender differences


Muscles and aging

-With aging there is a progressive decrease in the number and area of type 2 fibers
-Reduction of muscle mass and actual loss of motor units (denervation muscle atrophy), particularly in lower extremities
-But age presents no barrier to training adaptations of muscles
-Concentric strength declines sooner than eccentric strength, and arm strength declines more slowly than leg strength
-Highest strength levels: 20-40


Methods to enhance force production

-Neuromusclular adaptations
-Changes in muscle fiber type proportions and size
-Muscle hypertrophy
-Muscle hyperplasia


Neuromuscular adaptations

-Initial (first 4-6 weeks) results of resistance training are primarily due to neuromuscular adaptations
-Later (by 6 wks) muscle hypertrophy plays a larger role in increasing force production
-5 primary neuromuscular adaptations: 1) increased motor unit recruitment, 2) increased firing frequency of motor units, 3) increased motor unit synchronization, 4) increased activation of synergistic muscles, 5) increased inhibition of antagonistic muscles
-CNS and psychologic factors are important contributors to muscle strength


Changes in fiber type, hypertrophy, and hyperplasia 1

-Resistance training causes significant increase in fiber area of both type 1 and 2 (but mostly 2) fibers
-Hypertrophy of muscle predominantly caused by increased protein synthesis that results in larger muscle size
-Hypertrophy increases the nuclei in muscle cells and the synthesis of protein filaments that constitute the sarcomeres
-Eccentric muscle contraction results in more hypertrophy than concentric contractions


Changes in fiber type, hypertrophy, and hyperplasia 2

-There is no increase of mitos the ratio of mito to myofibrillar protein volume decreases (only for resistance training)
-Aerobic training improves cardiovascular fitness by increasing mito volume, # of mito, mito nzs, and capillary density
-No evidence yet of hyperplasia in humans


Exercise-induced muscle damage

-Delayed-onset muscle soreness (DOMS) due to:
-Microscopic tears in muscle tissue (causes release of creatine kinase, myoglobin, and troponin I)
-Osmotic press changes (edema)
-Muscle spasms
-Over stretching and tearing of connective tissue,
-Acute inflammation


Exercise-induced calcium entry

-When there is damage to the muscle fiber, large amounts of Ca may enter the cell
-The Ca may cause an autolytic process that degrades both contractile and non contractile structures


Factors contributing to development of muscle

-NS activation
-Physical activity
-Adrogens (steroids): increases protein synthesis and inhibits protein degradation
-Inhibition of myostatin: myostatin is a negative regulator of muscle mass (levels are elevated in wasting diseases), thus inhibiting it can increase muscle mass