ABSTRACT
Three types of muscle fibre are found in the adult: slow oxidative, fast oxidative, and fast glycolytic. Slow fibres are also known as type I fibres and fast fibres as type II (Table 24.3). All the muscle fibres of a single motor
Colour Red Red White
Primary source of ATP Oxidative phosphorylation
Oxidative phosphorylation
Glycolysis
Mitochondria, capillaries and myoglobin
+++ +++ +
Glycogen and glycolytic enzymes
+ ++ +++
Fatiguabililty + ++ +++
Contraction velocity + +++ +++
Fibre diameter motor unit size and diameter of motor neurone
+ ++ +++
unit are of the same type. Most muscles contain a mixture of the three fibre types. Muscles of posture, which are fatigue resistant, have a predominance of slow oxidative fibres. Muscles that are able to produce large forces for a brief period of time have a larger proportion of fast glycolytic fibres.
