Muscle types

There are three types of muscle in the body:

  1. smooth muscle – found in the internal organs and blood vessels - this is involuntary
  2. cardiac muscle – found only in the heart - this is involuntary
  3. skeletal muscle – attached to the skeleton - this is voluntary

Involuntary muscles are not under our conscious control which means we can't make them contract when we think about it.

Voluntary muscles are under our conscious control so we can move these muscles when we want to.

Question

Which muscle fibre types are not under conscious control?

Cardiac muscle and smooth muscle.

Muscle fibre types

There are three different types of skeletal muscles:

  • type I
  • type IIa
  • type IIx

Each type of muscle fibre has different characteristics which are shown in the table:

Type IType IIaType IIx
Speed of contractionSlowFastVery fast
Force producedLowMediumHigh
Resistance to fatigueHighMediumLow
ColourRedPinkWhite

Endurance cyclists need a high percentage of type I fibres so that their muscles can work for the duration of a race without getting tired. These muscles are red in colour because of the amount of capillaries that transport the oxygenated blood to the working muscles.

Cyclists in the Tour de France

A sprinter would need a high percentage of type IIx fibres so that their muscles can contract very quickly and produce a lot of force so that they can run very fast over a 100 m distance. However, these muscles tire very quickly so the sprinter will not be able to run at this speed for very long.

Usain Bolt wins the 100 metres
Question

Explain which muscle fibre type a long distance runner requires in order to be successful in their event.

They would need a high percentage of type I muscle fibres as they contract slowly with low force which would provide running movements at a slow pace. However, they can keep contracting for long periods of time without fatiguing which is required to run long distances.