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1-5 Muscle Metabolism and Training

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Production of ATP in Skeletal Muscle

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Muscle Fatigue

  • The inability to maintain force of contraction after prolonged activity
  • Due to:
    • Inadequate release of Ca2+ from SR
    • Depletion of CP, oxygen, and nutrients
    • Build up of lactic acid and ADP
    • Insufficient release of ACh at NMJ

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Oxygen Consumption After Exercise

  • Why do you continue to breathe heavily for a period of time after stopping exercise?
  • Oxygen debt = Oxygen recovery
    • Replenish CP stores
    • Convert lactate into pyruvate
    • Reload O2 onto myoglobin

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Isometric & Isotonic Contractions

  • Isometric muscle contraction
    • develops tension without changing length
  • Isotonic muscle contraction
    • Concentric
      • tension development while shortening
    • Eccentric
      • tension development while lengthening

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Muscle Contraction Phases

  • Isometric & isotonic phases of lifting a heavy box
  • Tension builds even though the box is not moving
  • Then muscle begins to shorten & maintains the same tension from then on

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Skeletal Muscle Fiber Types

  • Slow oxidative (Slow twitch; Type I)
  • Fast oxidative glycolytic (Intermediate; Type IIA)
  • Fast glycolytic (Fast twitch; Type IIB)

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Muscle Fiber Type: Speed of Contraction

Slow oxidative

  • Contract slowly due to slow myosin ATPases
  • Fatigue resistant
  • Smaller motor units
  • Aerobic
  • Abundant myoglobin, mitochondria, and capillaries

Fast oxidative

  • Contract quickly due to fast myosin ATPases
  • Moderate resistance to fatigue
  • Appear to be trainable
  • Aerobic
  • Intermediate myoglobin, mitochondria, and capillaries

Fast glycolytic

  • Contract quickly due to fast myosin ATPases
  • Easily fatigued
  • Abundant glycogen
  • Fewer myoglobin and mitochondria

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Strength and Conditioning

  • Factors that increase strength of contraction
    • muscle size and fascicle arrangement
    • size of motor units and motor unit recruitment
    • frequency of stimulations, length of muscle at start of contraction and fatigue
  • Resistance training (weight lifting)
    • stimulates cell enlargement due to synthesis of more myofilaments -- some cell splitting may occur
  • Endurance training (aerobic exercise)
    • produces an increase in mitochondria, glycogen & density of capillaries