Muscle Fiber Types

There are three types of muscle fibers, Type I (or slow twitch fibers), Type II (or fast twitch fibers) and Type III (or intermediate fibers). The slow twitch fibers provide endurance and aerobic capacity and are best built with high repetition, low resistance forms of exercise. The fast twitch fibers allow for more explosive powerful activities and develop with lower repetition, higher resistance training. Research suggests that the intermediate fibers have the capacity to become either Type I or Type II fibers depending on how they are stimulated. (Erin Boyton, MD, FRCSC)