fast-twitch (FT) fiber, a muscle fiber that can develop high tension rapidly. It is usually innervated by a single alpha neuron and has low fatigue resistance, low capillary density, low levels of aerobic enzymes, and low oxygen availability. FT fibers are used in such activities as sprinting, jumping, and weight-lifting. Also called fast-twitch muscle fiber. See also slow-twitch (ST) fiber.
