Fast-Twitch vs Slow-Twitch Muscle Fibers

Fast-Twitch vs Slow-Twitch Muscle Fibers

Fast-Twitch vs Slow-Twitch Muscle Fibers

Fast-twitch muscle fibers (Type II fibers) are those responsible for explosive movements such as sprints, box jumps, and power cleans.

Slow-twitch muscle fibers (Type I fibers) fire more slowly and can go for a longer time without getting fatigued.

Muscle fiber composition is largely determined by genetics. On average, people are born with a 50/50 ratio of fast and slow-twitch muscle fibers.

The variation from this average is seen in athletes that perform well in long distance running yet struggle to compete in sprints.

Fast-Twitch Muscle Fibers

Type II fibers can be broken down into 2 groups: Type IIa and Type IIb.
– IIa: known as intermediate fast-twitch fibers, more resistant to fatigue and quicker to recover.
– IIb: more powerful and faster fatiguing.

Type II fibers can generate more force than type I fibers. This is why athletes tend to focus on
training these fibers. But how much can you really impact your muscle type?

How to Train These Muscle Fibers

Whether or not an athlete can actually change slow-twitch into fast-twitch muscle fibers is highly debated. If we are box jump, fast-twitch muscle fibers exercisecapable of doing so, it is only at a marginal level. That’s why you don’t hear about athletes who excel at running distance races training to become the 100 meter champion later in their career.

In order to train your the desired muscle type, you must understand how to recruit that type of muscle.

The body recruits the muscles it needs based on the amount of force necessary to accomplish a task.

If the force required is low, you will use slow-twitch muscle fibers.

The more strenuous the task, the more you will activate your fast-twitch muscle fibers.

Exercises for training fast-twitch muscle fibers:
Heavy lifting. The closer to your one-rep max, the more beneficial.
Sprint work. Maximum effort sprints force your body to recruit maximum fast-twitch muscle fibers.
– Work to fatigue. When your slow-twitch muscle fibers get fatigued, they must recruit fast-twitch muscle fibers.

More details on training fast-twitch muscle fibers can be found here.

Slow-Twitch Muscle Fibers

Slow-twitch muscle fibers use oxygen more efficiently than fast-twitch to produce more ATP for more continuous muscle contractions.Jogging, slow-twitch muscle fibers exercise

This makes them useful for events like marathons and long bike rides.

Slow-twitch muscle fibers are the first fibers recruited during muscle activation.

If they are unable to generate enough force, then the fast-twitch muscle fibers are engaged.

How to Train These Muscle Fibers

Athletes are not typically interested in focusing on training slow-twitch muscle fibers, but you can see that they play an important role in sustaining long duration performance.

Exercises for training slow-twitch muscle fibers:
– Circuit training. Rotate through exercises with no break and zero to low weight.
– Body-weight exercises. Allows you to complete more reps and therefore longer time under tension.
– Isometric exercises. Keep your muscles under tension with no joint movement.
– Low weight resistance training. Slow reps to keep muscles under tension longer

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