Muscle Fibre Types/ Recruitment During Exercise & Recovery

• Types of Muscle Fibre Type

  • slow oxidative muscle fibres (SO)
  • fast glycolytic muscle fibres (FG)
  • fast oxidative glycolytic muscle fibres (FOG)
• Slow Oxidative Muscle Fibres (Type 1)


  Recruitment:

  • recover rapidly
  • ready for recruitment after 90s
  • aerobic work:relief ratios are very low
  • to maximise use 1:1 or 0.5 is used

  Characteristics:

  • small neuron size
  • high mitochondria density
  • high capillary density
  • high myoglobin levels

  Function:

  • high aerobic capacity
  • low anaerobic capacity
  • high fatigue resistance
  • low force on contraction
  • slow speed of contraction

  provide energy for sub-maximal aerobic work (marathon runner)
• Fast Oxidative Glycolytic Muscle Fibres (Type 2a)


  Characteristics:

  • large neuron size
  • moderate mitochondria density
  • high glycogen stores
  • moderate PC stores

  Function:

  • moderate aerobic capacity
  • moderate anaerobic capacity
  • moderate fatigue resistance
  • high force of contraction
  • fast speed of contraction

  used by middle distance runner (400 & 800m)
• Fast Glycolytic Muscle Fibres (Type 2b)

  Recruitment:

  • recruitment only in last 2-20s of contraction
  • near muscle exhaustion
  • long recovery time
  • causes DOMS 24-48hrs after exercise

  Characteristics:

  • large neuron size
  • high PC stores
  • high glycogen stores

  Function:

  • low aerobic capacity
  • high anaerobic capacity
  • low fatigue resistance
  • high force of contraction
  • fast speed of contraction

  used by sprinters