Lecture 22: Muscle Performance Office hours: Tuesday and Thursday 1-2pm in Gittings 108 or by appointment Extra office hours posted on D2L Claudia Stanescu, Ph.D.1. Compare and contrast the size, force-generating capabilities and metabolic characteristics of fast fibers (FG), slow fibers (SO), and intermediate fibers (FOG) Objectives: pp. 315-316, sec. 10.6 2. Define hypertrophy and atrophy in the context of muscle physiologyMuscle Performance Power Speed x Strength (Velocity) (Force) Endurance Sustained Activity type of metabolism aerobic vs. anaerobic Fiber Type...Fiber Types (skeletal muscle) 2. Fast fibers large diameter rapidly contracting anaerobic metabolism 1. Slow fibers small diameter slowly contracting aerobic metabolism 3. Intermediate fibers ‘medium’ diameter relatively fast primarily anaerobic Important: Within a motor unit, all fibers are the same typeSlow 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 Type IIa Type IIb Slow 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 mammalsSmall, S Medium, FFR Large, FF SO,Type I FOG,Type IIA FG,Type IIBMuscle 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 geneticallySuggested Learning Activities • Create a table to compare and contrast the characteristics of slow twitch and fast twitch muscle
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