Slow Twitch and Fast Twitch Muscle Fibres

Slow Twitch Fibres

Slow contraction
Work for a long time without fatigue
Good for endurance activities
High proportion found in muscle used for posture (i.e. back/calves)
Energy is released slowly through aerobic respiration in slow twitch muscle fibres
They have lots of mitochondria and blood vessels to supply the muscles with oxygen
Mitochondria are mainly found near to the edge of muscle fibres to there is a short diffusion pathway
Rich in myoglobin, a red coloured protein that stores oxygen (which gives muscles their red colour)

Fast Twitch Fibres

Quick contraction
Fatigues quickly
Good for short high intensity bursts
High proportions found in muscles used for fast movements (i.e. legs, eyes)
Energy is released quickly through anaerobic respiration using glycogen
Stores of PCr for quick energy release
Few mitochondria or blood vessels as they are not really needed as they produce their energy through glycogen – not oxygen.
No myoglobin (which gives them a pale white colour)