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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.

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:

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.

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.