muscle fibre types

Structural characteristics type I

·       Large number of mitochondria ·       Large number of capillaries ·       Large number of aerobic enzymes ·       High in myoglobin ·       Small in diameter ·       Wide Z line

Slow twitch muscle fibre type I

Suited to low intensity aerobic work, can be used for a long period of time without fatiguing.

Functional charachteristics type I

·       Use aerobic respiration ·       Slower force production ·       Slower to fatigue ·       High oxidative capacity ·       Slow twitch rate

Fast oxidative glycolytic muscle fibre type IIa

They allow fast contraction speed, produce a large force but fatigue easily. They are used in anaerobic work but can be improved through endurance training to increase their resistance to fatigue. 

structural charachteristics type IIa

·       Large number of capillaries ·       High in myoglobin ·       Intermediate diameter ·       Intermediate Z line thickness ·       Intermediate glycogen content

Functional charachteristics type IIa

·       Use aerobic respiration ·       Fast twitch rate ·       Intermediate resistance to fatigue ·       High oxidative capacity ·       High glycolytic capacity

Fast glycoltic muscle fibre type IIx

They allow very rapid contractions, produce large forces, however fatigue very easily. They are used in anaerobic work.

Structural charachteristics type IIx

• High in ATP

• High in PC

• Low in capillaries

• High myosin content

• Low in myoglobin

• Large diameter

• Large motor neurone size

• Low mitochondrial density

• Large motor unit size

• High number of fibres per unit

• High in ATPase

• High in Glycogen

• Narrow Z lines

• High in Creatine Kinase (anaerobic enzyme)

Functional charachteristics type IIx

· Use anaerobic respiration • High force production • High rate of relaxation • Low resistance to fatigue • Very high contractile speed • Fast nerve conduction • High glycolytic capacity