All muscles are made up of individual fibres, each containing myofibrils, which are small strands which work together to make your muscles contract.
Athletes with slow twitch fibres tend to do better in endurance events whereas athletes with fast twitch fibres tend to do better in events that require a short burst or powerful contraction. Watch the video below to find out more about muscle fibres.
Muscle fibres can either be slow twitch (type I) or fast twitch (type IIa and type II X).