3 Types of Muscle Fiber

There are 3 types of muscle fiber, all of which are important in a training program.

Type I are commonly known as slow-twitch fibers. These are the fibers that are good for endurance since they take a long time to fatigue. They also produce the least amount of force. The lower body is predominately made up of Type I fibers.

When your body needs more strength, it activates the Type II fibers aka fast-twitch fibers. They fatigue quicker than Type I. Your upper body is predominately Type II fibers.

There are two types of Type II fibers: Type IIa and Type IIx.

Type IIa fatigue moderately quicker than Type I so they are used for shorter periods of time. Think moderate distances and intensities for these fibers.

Type IIx fibers are recruited during explosive movements. They fatigue the quickest and are the fibers that are used when you need to do that big power move.

All three muscle fiber types play a role in endurance sports. Think about how long you can ride/run uphill or paddle in current before you start to fatigue (Type II fibers) vs going for long distances on a flat surface or paddle with no current (Type I fibers). That’s the different muscle fibers at play.

The amount of muscle fiber you have is mostly determined by your genetics, but with training you can increase the different fiber types.

If you need help with a training plan to maximize your power and endurance, contact us!