[Effie_drine]

Skeletal muscle tissue is composed of two general types of muscle fibers - fast-twitch and slow-twitch. Fast-twitch muscle fibers are selectively recruited when heavy work is demanded of the muscles, and strength and power are needed. They contract quickly, providing short bursts of energy, and are therefore used for high-intensity, low-endurance activities, such as sprinting, weightlifting, shot-putting, and swining a golf club. However, fast-twitch muscle fibers become exhausted quickly. Pain and cramps rapidly develop from the buildup of lactic acid, which is a byproduct of the metabolism of this kind of muscle fiber.
Slow -twitch muscle fibers produce a steady, low-intensity, repetitive contraction. They do not tire easily and are recruited when endurance is needed. Therefore, slow-twitch muscle fibers are used for low-intensity, high-endurance activities, such as long distance running.

The duration and intensity of your activity will influence the physiology of your muscle tissue and the development of your muscle fibers. Endurance athletes tend to develop a greater percentage of slow-twitch muscle fibers, while power athletes tend to develop a greater percentage of fast-twitch muscle fibers. One reason for this is that in power athletes, the fast-twitch muscle fibers increase in size to store more ATP and CP. ATP and CP are needed for explosive energy. Another reason is that power athletes need more muscle glycogen to fuel their muscles, while endurance athletes need both muscle glycogen and fatty acids.

[Liftingchic]

a good read for newbies..




LC

[FrenchBread]

And don't forget the white muscle fibers and red muscle fibers...hehe

[buckett]

Muscle groups in the body are comprised of two types of fibers: Slow-twitch and Fast-twitch. slow muscles are more efficient at using oxygen to generate more fuel. fast-twitch muscle fibre for speed, power and strength.