Muscle Fiber Composition: Are You a Fast-Twitcher or a Slow-Twitcher? Here’s How to Find Out

Muscle Fiber Composition: Are You a Fast-Twitcher or a Slow-Twitcher? Here’s How to Find Out

(Last Updated On: April 19, 2019)

istock_000006641034xsmall-1Muscle fibers make it possible for you to run, jump or lift a weight. One type of muscle fiber called slow-twitch muscle fibers is made for endurance-type activities such as running long distances, cycling long distances. They contract with less force but are more resistant to fatigue, which makes them perfect for running long distances at a moderate pace. The other primary type of muscle fiber called fast-twitch fibers contract with greater force than slow-twitch fibers but become fatigued very quickly. They come into play for moves that require power such as lifting a heavy weight or sprinting.

The average person has a roughly equal ratio of slow-twitch to fast-twitch muscle fibers, but some people genetically have a greater ratio of one type of muscle fiber over the other. This gives them an advantage in certain types of sports. Have you ever wondered what the fiber composition of your muscles is? Here’s a simple test that will give you a rough idea of what your own muscle fiber composition is.

What Kind of Muscle Fiber Composition Do You Have?

This is a quick test using weights that will tell you whether you have more of one muscle fiber type than another. It’s called the D.F. Hatfield muscle fiber test. Enjoy the results, but keep in mind it’s only an approximation. The only way to know the true fiber composition of your muscles is to do a muscle biopsy.

Start by determining what your one repetition maximum is. You can do this in our free online Workout Manager. This is the amount of weight you can lift with good form only once. Once you know your one-rep max, choose a weight that’s 80% of that value. Rest 15 minutes before starting, then do as many repetitions as you can do with good form using your chosen weight.

If you can lift the weight more than 8 times, you probably have a predominance of slow-twitch muscle fibers. On the other hand, if you can’t do 7 repetitions, you’re fast-twitch dominant. If you can lift the weight 7 or 8 times, you likely have a pretty equal ratio of fast-twitch to slow-twitch muscle fibers.

What Do the Results Mean?

If you’re slow-twitch dominant, you may have some natural advantage when it comes to endurance-type activities such as long distance running. On the other hand, if you have a higher ratio of fast-twitch to slow-twitch muscle fibers, you may be a natural for sports that require sprinting, jumping or power moves.

Of course, the muscle-fiber type is only one factor when it comes to success in any sport. Just because you have more of a certain fiber type doesn’t necessarily mean you’ll maximize that potential. Training, motivation and other factors like nutrition play a role too.

Knowing your predominant muscle fiber type can help you get better results from your training. If you have a predominance of fast-twitch fibers, your muscles may respond better to heavier weights and lower reps. If you’re a slow-fiber type, an endurance-type workout using a lighter weight and more repetitions may be more beneficial for your muscle type. At the very least, it’s interesting to know what ratio of muscle fibers you have.



Exercise Physiology. Fifth edition. 2001. McArdle, Katch, and Katch. “The Magic Workout: Is There Such a Thing?”


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3 thoughts on “Muscle Fiber Composition: Are You a Fast-Twitcher or a Slow-Twitcher? Here’s How to Find Out

  1. I think I’d rather have the muscle biopsy. ; ) Just kidding! lol Thought that was a pretty good slow-twitch joke!

    Maybe not. Ha!

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