Lecture 22 Muscle Performance Claudia Stanescu Ph D Office hours Tuesday and Thursday 1 2pm in Gittings 108 or by appointment Extra office hours posted on D2L Objectives pp 315 316 sec 10 6 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 Muscle Performance Power Speed x Strength Velocity Endurance Force Sustained Activity type of metabolism aerobic vs anaerobic Fiber Type Fiber Types skeletal muscle 1 Slow fibers small diameter slowly contracting aerobic metabolism 2 Fast fibers large diameter rapidly contracting anaerobic metabolism 3 Intermediate fibers medium diameter relatively fast primarily anaerobic Important Within a motor unit all fibers are the same type 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 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 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 Type I Slow Type IIa Type IIb Fast dark meat vs white meat 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 Muscle composition 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 Suggested Learning Activities Create a table to compare and contrast the characteristics of slow twitch and fast twitch muscle fibers
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