Muscle fibers

Muscle fibers are the individual contractile units of a muscles. They can be roughly divided into slow-twitch fibers (Type I, for muscular endurance) and fast-twitch fibers (Type II, for quick power and maximum strength). Depending on the type of training, different muscle fiber types are more heavily utilized. Targeted training that emphasizes both concentric and eccentric phases promotes the growth and adaptability of the fibers.