5 FA Muscular Actions/Creation of Movement

• Characteristics of skeletal muscle


  • Excitability
  • Contractibility
  • Extendibility
  • Elasticity
• Improving nervous muscle function (contractability)


  1. Disinhibition

  2. Increased firing rate of motor units

  3. Improved synchronisation of firing rate of motor units

  4. Improved technique/muscle coordination
• All-or-none principle


  All the muscle fibres in a motor unit will either contract with 100% force or not at all
• Contraction and relaxation of a muscle is activated via nerve impulses
• Potassium and magnesium


  Act as "messengers" to control contraction and relaxation of muscles
• Fatigue is the most common symptom of a potassium and magnesium deficiency
• To increase the strength of contraction, the brain sends more signals resulting in the recruitment of more motor units
• Smooth muscle


  • Located in the walls of hollow internal structures
  • Involuntary, non-striated
  • Less powerful than skeletal muscles, can contract indefinitely without fatiguing
• Cardiac muscle


  • Muscle of the heart
  • Striated and can contract rapidly
  • Contraction is involuntary and fatigue resistant
• Skeletal muscle


  • Attached to bones by tendons
  • Responsible for moving the skeleton via contraction
  • Striated in appearance
• Characteristics of fast and slow twitch muscle fibres


  • Contraction Speed
  • Motor Neuron size & frequency
  • Colour
  • Resistance to Fatigue
  • Energy System used for muscle contraction
  • Force Production
  • Capillary Density
  • Oxidative Enzymes Density
  • Major Fuel Source for muscle contractions
• Force production


  Result of the cross bridge formation between the actin & myosin filaments sliding past each other
• Fast twitch fibres have a higher threshold and will be activated only when the force demands are greater than the slow twitch fibres can meet
• Fast twitch fibres also have a much stronger contractile force because the motor neuron carrying the impulse is larger, and the muscle fibres are stronger & thicker
• The downside of fast twitch fibres is they also fatigue quickly
• Percentage of muscle fibre types in different athletes


  • Marathon runner
  • 400m
  • 100m
  • Hockey
  • Squash
  • Sprint swimming
  • Sprint running
  • Long distance swimming
  • Cycling
• Preferential recruitment of muscle fibres


  1. Type 1 fibres recruited for low intensity exercise

  2. Type IIa fibres recruited for high intensity exercise

  3. Type IIb fibres recruited for very high intensity exercise