They contract slowly and can work for a long period of time without getting tired. This makes them good for endurance activities, e.g long distance running and maintaining posture.
High proportions of slow twitch muscle fibres are found in the muscles you use for posture, such as the muscles in your back and calves.
Energy is released slowly by aerobic respiration in slow twitch muscle fibres.
They have lots of mitochondria and blood vessels to supply the muscles with oxygen.
The mitochondria are mainly found near the edge of muscle fibres, so that there's a short diffusion pathway for oxygen from the blood vessels to the mitochondria.
Slow twitch muscle fibres are also rich in myoglobin, so they appear reddish.
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Fast twitch muscle fibres
They contract very quickly but also get tired quickly.
This makes them good for short bursts of speed and power, e.g sprinting and eye movement.
High proportions of fast twitch muscle fibres are found in muscles you use for fast movement such as the legs, arms and eyes
Energy is releases quickly through anaerobic respiration using glycogen in fast twitch muscle fibres. They also have stores of PCr so that energy can be generated very quickly when needed.
Fast twitch muscle fibres have few mitochondria and blood vessels. They don't have much myoglobin either, so they can't store much oxygen - this gives them more of a whitish colour.
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