Training Different Muscle Fiber Types

I had a conversation with a friend the other day and I came to realize that, unless you study the body, the vast majority of people really don't understand muscle fiber types and why you train different muscle groups differently. The conversation was from a body-building/muscle hypertrophy standpoint, but the same can be said for performance training, as well.

So here's the story: Muscles in your body are made up of different type of muscle fibers, with the type denoting how quickly they can contract and, related to this, the different bioenergetics of each fiber. The muscle-fiber continuum is: Type I, Type IIc, Type IIac, Type IIa, Type IIax, Type IIx, with Type I being the slowest to fire but also the slowest to fatigue, and Type IIx being on the exact opposite end of the spectrum.

But why is this important to know if you are just trying to lift for aesthetic reasons? Well, because of the differences in how quickly each muscle fiber type fatigues, each type also displays different rep ranges, or more specifically times under tension, by which they optimally perform hypertrophy.

A couple examples are the hamstrings and calves. Hamstrings are predominantly Type II, fast twitch fibers in the majority of people, unless they have trained themselves to perform otherwise. This means that with hamstrings you really shouldn't go about 12 reps in a strength training set because they will begin to lose their fast-twitch characteristics. Calves are comprised of two main muscles--the gastrocnemius and the soleous. The gastroc is comprised of mainly fast-twitch muscle fibers, so it responds to heavier sets of less reps, while the soleous is more slow-twitch fibers, so it responds better to higher reps at lower weights.

As a basic rule of thumb, you can identify whether a muscle is fast-twitch or slow-twitch dominant by asking yourself, "Is the muscle used for form or for function?" In other words, it is a postural, tonic muscle, or is it an explosive-movement, phasic muscle?

Answer that question for yourself and apply those answers to your training to see increased results.

Get big or die tryin'.