muscle fibres

• motor unit


  A motor neurone and all of the muscle fibres it stimulates
• three main types of muscle fibres

  slow twitch type 1

  fast twitch type 11A

  fast twitch type 11X
• muscle fibres info

  • our skeletal muscles contain a mixture of all 3 types but not in equal proportions you cant change your fibres however you can train to improve the different fibre typesyou can increase the size of muscle fibres through training ( hypertrophy )
  • the mix is genetically determined so the relative proportion of each type varies
• structural characteristics of type 1

  muscle fibre diameter - small

  mitochondrial density - high

  capillary density - high

  myoglobin content - high

  PC stores - low

  glycogen stores - low
• structural characteristics of type 11X

  • muscle fibre diameter - large (biggest)
  • mitochondrial density - low
  • capillary density - low
  • myoglobin content - low
  • PC stores - very high
  • glycogen stores - very high
• what does the motor neurone do

  transmits the nerve impulse to each muscle fibre
• sporting examples for each type

  type 1 - marathon

  type 11X - 100m sprint or weight lifting

  type 11A - 1500 m race
• functional characteristics of type 1

  contraction speed - slow

  motor neurone conduction speed - slow

  force production - low

  fatigability - low

  aerobic capacity - very high

  anaerobic capacity - low

  ATP ASE activity - low
• functional characteristics of type 11X

  contraction speed - fast

  motor neurone conduction speed - fast

  force production - high

  fatigability - high

  aerobic capacity - low

  anaerobic capacity - very high

  ATP ASE activity - very high
• 7 ways to increase force of contraction

  1. Larger motor units will be recruited

  2. More motor units can be recruited (MULTIPLE UNIT SUMMATION)

  3. Fast twitch 11X muscle fibres recruited rather than slow

  4. Sequence of impulses sent to muscles will reach the threshold to allow ALL fibres to contract together (ALL OR NONE LAW)

  5. Muscle repeatedly stimulated with no time to relax (WAVE SUMMATION) = produces a forceful contraction known as TETANIC CONTRACTION

  6. The number and size of motor units will be rotated to delay fatigue (SPATIAL SUMMATION)

  7. PROPRIOCEPTORS detect changes in muscle length, send info to brain which compares info to memory to ensure correct force applied based on previous experiences