Muscle Performance Claudia Stanescu Ph D Office Hours in Gittings 108 Tue 10 11am and Thurs 1 2pm or by appointment Objectives 1 Compare and contrast the size force generating capabilities and metabolic characteristics of fast fibers FG slow fibers SO and intermediate fibers FOG 2 Define hypertrophy and atrophy in the context of muscle physiology 3 Describe the effect of endurance and resistance training on muscle Muscle Performance Power Speed Velocity Endurance x Strength Force Sustained Activity type of metabolism aerobic vs anaerobic Fiber Type Fiber Types skeletal muscle 1 Fast fibers 2 Slow fibers 3 Intermediate fibers large diameter rapidly contracting anaerobic metabolism small diameter slowly contracting aerobic metabolism medium diameter relatively fast primarily anaerobic Important Within a motor unit all fibers are the same type Fast Fibers also called FG for fast glycolytic or Type IIb 1 Large diameter generate large force because tension is proportional to cross sectional area many sarcomeres in parallel many cross bridges per fiber 2 High speed fast myosin ATPase 3 Low resistance to fatigue relies on glycolysis low aerobic capacity few mitochondria low myoglobin content Slow Fibers also called SO for slow oxidative or Type I 1 Small diameter generate low force few sarcomeres in parallel few cross bridges per fiber 2 Low speed slow myosin ATPase 3 High resistance to fatigue relies on aerobic metab high aerobic capacity many mitochondria high myoglobin content dense capillary supply for O2 delivery Intermediate Fibers called FOG for fast oxidative glycolytic or Type IIa 1 Intermediate diameter generate intermediate force 2 Moderate speed intermediate myosin ATPase 3 Intermediate resistance to fatigue primarily relies on glycolysis but has much higher aerobic capacity than FG fibers Myoglobin 153 amino acid protein containing a heme iron group at the center Binds and releases oxygen Responsible for muscle s red color Abundant in diving mammals Small S SO Type I Medium FFR FOG Type IIA Large FF FG Type IIB Training Effects Most muscles are mixtures of Fast and Slow motor units in humans a 50 50 mixture is common with much individual variability The proportion of Fast vs Slow motor units is determined genetically Training Effects on skeletal muscle Endurance training Increased mitochondrial number oxidative enzymes Increased capillary density Strength training Increased fiber diameter hypertrophy Increased glycolytic enzymes Some increase in capillary density for removal of wastes Muscle Hypertrophy and Atrophy Repeated exhaustive stimulation increases muscle mass hypertrophy 1 addition of more myofibrils diameter not more cells i e not hyperplasia 2 increase in mitochondrial and glycolytic enzymes Synthesis of new mass stimulated by androgen male hormones males tend to get bigger muscles A decrease in stimulation leads to a loss of muscle mass atrophy