PSIO 201 5th Edition Lecture 22 Outline of Last Lecture Muscle Performance Outline of Current Lecture Current Lecture Power Speed x Strength Endurance Sustained Activity Fiber Types skeletal muscle within a motor unit all fibers are the same type 1 Slow Fibers small diameter slow contracting aerobic metabolism 2 Fast Fibers large diameter rapidly contracting anaerobic metabolism 3 Intermediate Fibers medium diameter relatively fast primary anaerobic Slow Fibers Type I or SO small diameter few sarcomeres in parallel Low speed slow myosin ATPase High resistance to fatigue relies on aerobic metabolism many mitochondria high myoglobin and dense capillary supply Fast Fibers Type IIb or FG Large in diameter large force because many crossbridges High speed fast myosin ATPase Low resistance to fatigue relies on glycolysis few mitochondria low myoglobin Intermediate Fibers Type IIa or ROG Intermediate diameter intermediate force Moderate speed Intermediate resistance to speed Training Effects Most Muscles are mixtures of fast and slow motor units humans have 50 50 mixture with much individual variability Proportion of fast vs slow motor units is determined genetically Effects on Skeletal Muscle Endurance training increased mitchochondrial number oxidative enzymes Increased capillary density Strength Traininig increased fiber diameter Increased glycolytic enzymes Some increase in capillary density Muscle Hypertrophy and Atrophy Repeated exhaustive stimulation increases muscle mass hypertrophy 1 addition of more myofibrils diameter 2 increase in mitochondrial and glycolytic enzymes a decrease in stimulation leads to a loss of muscle mass atrophy
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