Fast-Twitch VS Slow-Twitch: What is the difference and does it really matter?


What kind of cyclist are you? Do you find it more important to outsprint the girl riding next to you or would you rather be able to ride for hours and hours without wearing down? Believe it or not, some of this is genetically determined. Our athletic strengths whether we are a sprinter or an endurance rider often depend on our muscle fiber composition.

Muscle Types:

Slow Twitch (Type I)
The slow muscles are more efficient at using oxygen to generate more fuel (known as ATP) for continuous, extended muscle contractions over a long time. They fire more slowly than fast twitch fibers and can go for a long time before they fatigue. Hence,slow twitch fibers are very useful for endurance athletes who cycle for hours on end.

Fast Twitch (Type II)

Because fast twitch fibers use anaerobic metabolism to create fuel, they are much better at generating short surges of strength and/or speed than slow muscles.

However, they fatigue more rapidly. Fast twitch fibers generally produce the same amount of force per contraction as slow muscles, but they get their name because they are able to fire more quickly. Having more fast twitch fibers can be advantageous to a sprinter since she needs to quickly generate a lot of force, in a short period of time.

What’s my type? Can we alter our Fast-Twitch/Slow-Twitch composition?

If you are anything like me…you are now wondering what type of muscle fibers you have. It is generally thought that most people have close to a 50/50 balance of fiber types. The only way to know for sure, is to have a muscle biopsy. In order to do a biopsy, a small amount of tissue is cut out of your muscle and analyzed. Although it would be quite interesting (but very painful), this procedure is practically useless! Even if you know your fiber-type distribution, there is not much you can do about it. You can however, improve other physiological characteristics with your training which can modify or get your muscle fibers to act differently.

For instance: If you’re genetically dispositioned to be a sprinter, you can still compete in endurance events. You can train to develop/modify slow-twitch fibers by doing lower resistance with higher repetitions, or longer durations with lower intensities.

What does it really mean?

While fiber types are undoubtedly very important. I believe that diet, training regimens, mental attitude and rest are ultimately deciding factors in whether we are successful athletes or not. Don’t believe that just because your genetics may position you to be better at endurance riding that you can’t also become a sprinter. In the end…you have the choice! Do what makes you happy! With enough persistence and solid training, you can be successful in whatever it is you want to do!

Felicia is a Moxie Cycling Ambassador and blog contributor. Check out her bio here!

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