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Fast-Twitch vs. Slow-Twitch Muscle Fibers

What Are The Differences?

We have two general types of muscle fibers: slow-twitch (type 1) and fast-switch (type 2). In this article we will help you understand their differences.

What are slow-twitch muscle fibers?

Slow-twitch muscle fibers contract slowly and have a low potential for muscle growth. They’re more resistant to fatigue, which make them suited for endurance sports such as long distance running, swimming, etc. They tend to recover faster than fast-twitch fibers.

What are fast-twitch muscle fibers?

Fast-twitch muscle fibers contract quickly and have much greater potential for muscle growth than slow-twitch. They tend to fatigue faster than slow-twitch and take a longer time to recover.To be more precise, there are two kinds of type 2 muscle fibers:

  • Type 2A: moderately fast-twitch. Suited for moderate and high intensity activities, e.g. a 400m run.
  • Type 2B: extremely fast-twitch. Suited for high intensity activities, e.g. a 100m run.

Slow and fast-twitch muscle fibers ratio

All muscle groups contain more or less 50% of fast-twitch and 50% of slow-twitch muscle fibers. The lower body tends to have more slow-twitch muscle fibers than the upper body. Some people might have more of one type of fibers, but it’s not such a big difference. Although genetics play a major role regarding your performance in on activity, most people can perform in both endurance and power activities.

How the body uses slow-twitch and fast-twitch muscle fibers?

When you’re performing an exercise, your body first uses slow-twitch fibers and then uses fast-twitch fibers. As you get closer to your maximal effort (failure) your body recruits all types of muscle fibers.

Therefore, you can train your muscles according to your activity. A strength athlete would mainly train their fast-twitch muscle fibers, whereas a marathon runner would primarily focus on slow-twitch fibers. However, you can also focus on both types of muscle fibers. Me for example, I like to perform both aerobic and anaerobic workouts.

In summary

  • There are two general types of muscle fibers: slow-twitch (type 1) and fast-switch (type 2).
  • Slow-twitch muscle fibers are suited for endurance sports.
  • Fast-twitch muscle fibers are more suited for moderate to high intensity sports.
  • The fast/slow-twitch muscle fibers' ratio varies from muscle, but it is more or less: 50% / 50%.
  • Your body first uses slow-twitch muscle fibers then uses fast-twitch muscle fibers as you get closer to failure.

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