PSIO 201 5th Edition Lecture 22 Outline of Last Lecture Muscle PerformanceOutline of Current Lecture Current LecturePower Speed x Strength Endurance Sustained Activity Fiber Types (skeletal muscle) – within a motor unit, all fibers are the same type1. Slow Fibers- small diameter, slow contracting aerobic metabolism2. Fast Fibers- large diameter, rapidly contracting anaerobic metabolism3. Intermediate Fibers- medium diameter, relatively fast primary anaerobicSlow 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 myoglobinIntermediate Fibers: Type IIa or ROG- Intermediate diameter – intermediate force - Moderate speed- Intermediate resistance to speedTraining EffectsMost Muscles are mixtures of fast and slow motor units : humans have 50:50 mixture, with much individual variabilityProportion of fast vs. slow motor units is determined geneticallyEffects 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 densityMuscle Hypertrophy and AtrophyRepeated, exhaustive stimulation increases muscle mass: hypertrophy1. addition of more myofibrils (diameter)2. increase in mitochondrial and glycolytic enzymesa decrease in stimulation leads to a loss of muscle mass:
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