CrossFit Strength

Fast-twitch?

I’d like to cover each of CrossFit’s 10 general skills over the next few weeks, and since I enjoy the strength component so much I thought I’d start off talking about it.

CrossFit defines strength as “The ability of a muscular unit, or combination of muscular units, to apply force.” Which is a good general description of strength, but let’s see if we can’t delve a bit deeper into the topic.

Our muscles are made up of different types of muscle fibers which rely on different types of energy systems and support the body in different ways. The fibers can grab onto each other and pull which produces the muscle contraction. The fibers can be broken down into two types of muscle fiber, slow-twitch and fast-twitch.

Slow-twitch fibers have a slow contraction time (go figure) and are functionally responsible for aerobic activities requiring low-level force over a longer period of time. Slow-twitch are smaller in diameter than their fast-twitch kin.

Fast-twitch fibers generate quick force but are susceptible to fatigue. They are further broken down into type IIa and type IIb. Type IIa are the intermediate fibers between the Slow-twitch and Fast-twitch IIb. They can use both aerobic and anaerobic metabolism to create energy. Type IIb muscles are the classic fast twitch muscle that is used to lift large loads quickly! These guys get fatigued fast but they pack a wallop.

As muscles are engaged the slow-twitch fibers have the lowest firing threshold and are recruited first, as larger forces are applied(think heavy loads) the fast-twitch fibers are recruited.

People have different quantities of each type of fiber and a general rule is that our fiber type will influence what we are naturally good at. Someone with a larger amount of fast twitch fibers will likely lift more than a slow-twitch dominant. A slow twitch dominant will be predisposed to being a better distance runner.

So if you already know you’re slow-twitch dominant what’s the use of competing in a lift against a fast-twitcher? Just like everything else, training comes into effect and there are studies that indicate that you can change your  body’s fiber type distribution based on training. We always stress in CrossFit that consistency will get you there…

Slow-Twitch