Speed is the ability of the body to perform similar movements consecutively at the fastest rate. The following factors determine the speed.
(a) Nervous system and its mobility: To generate more speed the muscles have to contract and relax at maximal speed. These actions are possible when moter impulses from C.N.S. initiates. So we call it as mobility of nervous system.
(b) Composition of muscle fibres: The muscles which have more percentage of fast twitch fibre contract with more speed than in comparison to the muscles which have less percentage of slow twitch muscle fibres. The muscle composition is genetically determined. The sprinters always have more fast twitch fibres and endurance runners have more of slow twitch fibres
(c) Flexibility: Every individual has different levels of flexibility. Better flexibility around a joint gives more range of movement to the muscle which can be helpful in generating better speed.
(d) Explosive Strength: It is the ability, of muscles to overcome resistance as fast as possible with sub-max intensity of stimulus. It is a combination of strength and speed abilities, eg. 100 m sprint start, take off in long jump.