T Nation

Muscle Fiber Type

How can I find out what type of muscle fibers my body has? Does it have fast-twitch or slow-twitch? How can I test myself? Thank you!

does it matter?

The only 100% effective way of determining muscle fiber distribution is to get a biopsy. This is very painful and can only be done in a physiology lab (so it can be constly).

The is a way to approximate fiber composition. We know that slow twitch fibers are more enduring than fast twitch fibers. By establishing the number of repetitions you can do with 80% of your max on a certain lift you can get a relatively good idea of your fiber makeup.

  1. If you do between 4 and 6 reps with 80% the muscles you are exercising are mostly fast twitch dominant.

  2. If you do 12-20 reps with 80% the muscles you are exercising are mostly slow twitch dominant.

  3. If you can do between 7 and 11 reps the muscle is about equal in slow and fast twitch fibers.

even biopsy leaves much to be desired where different parts of a “muscle” can have different compositions like the heads of the deltoid or various components of the
‘Lats’

You can also induce fiber type conversion through the type of training you do. Through a heavy emphasis on endurance training, you can get some fast twitch fibers to take on slow-twitch characteristics and some to actually convert to a slow-twitch makeup and vice-versa with a heavy emphasis on short-duration explosive training. Unless you are almost completely slow-twitch, it makes sense to train for fast-twitch growth as there is significantly more hypertrophy potential in the fast-twitch fibers.

I would also like to know if it matters. I seem to be more fast-twitch…Should I train a certain way, or, with a certain amount of reps?

depends on your goals. in the over simplified case if you are mostly slow twitch and just want “to get big” youd just train with higher reps 10+. however if you have other goals…