Muscle Fiber types

Type 1 Fibers

Slow twitch. Long contraction time. High resistance to fatigue. Small motor neuron. Low force production. Low in glycogen, high in triglyceride (fat). Used for aerobic activities such as posture, walking, and jogging.

What are the three types of muscle fibers?

Type 1, Type 2a, Type 2b

Twitch

When a muscle is stimulated so that some of its motor units are activated, it contracts and then releases.

Type 2a Fibers

Fast twitch (FTA). Fast contraction time. Intermediate fibers (fast-oxidative glycolytic). Large motor neuron. Moderate resistance in fatigue. Very adaptable via training. Stronger force production. High in glycogen, moderate in triglyceride. Used for activities requiring larger forces over a longer time, such as swimming, cycling, and running.

Type 2b

Fast twitch (FTB). Fast-glycolytic fibers. Fastest contraction time. Very sensitive to fatigue. Large motor neuron. High force production. High in glycogen, low in triglyceride. Used for activities requiring large forces over a short time, such as sprinting, jumping, throwing, and weightlifting.

Muscle Fiber type facts

Human skeletal muscles are never solely fast twitch or slow twitch. Fiver type composition determined genetically. Untrained subjects: 50% ST, 50% FT. No difference between males and females.