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Muscle - Temperature Effects

Muscle - Temperature Effects. Gross efficiency Eff = Mechanical Work (J)/Energy (J) x 100 = %. Muscle - Temperature Effects. Human joint movement is about 20% efficient for an isolate muscle/joint system Higher with walking, running Therefore, up to 80% of energy heat.

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Muscle - Temperature Effects

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  1. Muscle - Temperature Effects • Gross efficiency • Eff = Mechanical Work (J)/Energy (J) x 100 = %

  2. Muscle - Temperature Effects • Human joint movement is about 20% efficient for an isolate muscle/joint system • Higher with walking, running • Therefore, up to 80% of energy heat

  3. Positive Effects of a Warm-up • Joint • Decreases synovial fluid viscosity • Muscle • Increases metabolism (Q10 effect) • Increases blood flow • Increases efficiency • Decreases muscle viscosity • Decreases internal work • Increases maximal velocity • Increases power • Does NOT change maximal isometric tension

  4. Warm-up - Force, Power

  5. Temperature and Muscle Function • Muscle function is most efficient at a body temperature of about 38.50 C (or 1010 F) • Higher body temperatures require heat elimination • Increased skin blood flow • sweating • Precautions needed • Limit work, appropriate clothing • Fluid replacement

  6. Types of Skeletal Muscle Fibers • Classification based on time to reach maximum tension (twitch) • Slow-Twitch (ST) • Fast-Twitch (FT)

  7. Tension Developed Over Time in Muscle Fibers 100 ms

  8. Types of Skeletal Muscle Fibers • Type I • Slow-Twitch Oxidative (SO) (red) • Type IIa • Fast-Twitch Oxidative, Glycolytic (FOG) (pink) • Type IIb, IId • Fast-Twitch Glycolytic (FG) (white) • All fibers in a single motor unit are the same type

  9. Histochemical Staining of Fiber Type Type IIb Type IIa Type I

  10. Muscle Fiber Types I (SO) IIa (FOG) IIb (and IId) FG Speed slow fast fast Color red pink white Mitochondria many moderate few Fuel fat > CHO fat & CHO CHO > fat Fatigue slow moderate fast Fiber x-sect. small medium large Nerve x-sect small medium large Blood supply high medium low ECM larger medium least Efficiency highest medium lowest

  11. Recruitment of Motor Units- Exercise • Size principle for motorneurons • Smallest diameter recruited first • Type I (SO): rest, standing, AND higher intensity • Related to lower intensity endurance activities (long distance running – marathon, etc) • Type IIa (FOG): 40% VO2max and higher • Related to higher intensity activities requiring endurance (middle distance running: 1500 m, 5000 m) • Type IIb (FG): 70% VO2max and higher • Related to high intensity short duration activities (sprint races – 60 m, 200 m, etc)

  12. Skeletal Muscle Fiber Types • Humans: Type I, Type IIa, Type IId (similar to IIb) • Proportions vary widely among different muscles and different people • But: most people are ~50% ST; 50% FT • World-class sprinters may be 75% FT (genetic) • No training regimens can increase % FT!! • Techniques/biomechanics for enhancing speed • % FT does increase in certain pathologies: • Spaceflight • Muscular dystrophy • Hyperthyroidism • Spinal injury

  13. Muscle Fiber-Types: Training • most people are ~50% ST; 50% FT • Endurance training • May result in a small shift • IIb/d IIa • IIa I? • Some fast to slow shift in myosin (isoform) types

  14. Fiber-type composition - athletes

  15. Fiber-type composition --> Force FT • Larger fiber diameter • More force/area Powers & Howley

  16. Fiber-type composition -> Power FT • More force • Higher velocity P = F • v

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