Muscle Fibres

• Muscle fibers


  Different types that allow us to do different activities and participate in different sports
• Muscle fiber types


  • Type 1 (slow twitch or slow oxidative)
  • Type 2A (fast oxidative glycolytic)
  • Type 2X (fast glycolytic)
• Type 1 (slow twitch or slow oxidative) muscle fibers


  • Small neuron size with few muscle fibers
  • Produce low levels of force
  • Slow contraction speeds
  • Red in color indicating high number of capillaries and good blood/oxygen supply
  • High number of mitochondria for aerobic energy production
  • Very resistant to fatigue
• Events suited to Type 1 muscle fibers

  • Marathons
  • Triathlons
• Type 2A (fast oxidative glycolytic) muscle fibers


  • Large neuron size with many muscle fibers
  • Moderate capillary density and mitochondria levels
  • Fast contraction speeds
  • High force production
  • Moderate resistance to fatigue
• Events suited to Type 2A muscle fibers

  • 400m
  • 800m
• Type 2X (fast glycolytic) muscle fibers

  • Large neuron size with many muscle fibers
  • Very low capillary density and mitochondria levels
  • Very fast contraction speeds
  • Very high force production
  • Very low resistance to fatigue
• Events suited to Type 2X muscle fibers

  • 100m
• Muscle fibers are a combination of the 3 types, not purely one type
• Genetics play a role in the proportion of muscle fiber types, but training can shift the balance between type 2A and 2X fibers
• Work:rest ratio


  The ideal work period and recovery period for training different muscle fiber types
• Work:rest ratio for Type 1 muscle fibers

  • 1:1 or 1:0.5 (work period : rest period)
  • Shorter rest periods as endurance training doesn't cause significant muscle damage
• Work:rest ratio for Type 2 muscle fibers

  • 1:3+ (work period : rest period)
  • Longer rest periods needed due to higher force production and faster fatigue
• Type 2 muscle fibers should not be trained within 4-10 days of a previous high-intensity workout to allow for recovery and adaptation