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Muscle Fiber Dominance/Frequency of Use

Pure hypothesis, but…

Do you guys feel there is at least a correlation between the dominant fiber type within a muscle, and how frequently muscle tends to be used? If so, would this suggest what type of training stimulus would be more optimal for hypertrophy?

I know it’s been written by some coaches that fast-twitch dominant muscles should be trained with higher reps and lighter loads (I believe that’s what I’ve read), but I’m curious if the opposite isn’t better for hypertrophy.

For example, say the calves are used frequently since the muscles are stimulated even during walking.

What is the likelihood that the opposite type of loading - i.e. heavy loading, fewer reps - would be better for hypertrophy for that muscle, since the chronic stimulation that muscle receives is usually in the form of lower force contractions/higher reps (i.e. walking, etc) ? The goal being to shock the muscle with un-natural stimulus.

Can a muscle’s dominant fiber makeup be determined by the role the muscle plays in average, day-to-day function?

If so, would it be better to provide the stimulus that is un-natural for the muscle, e.g. heavy load / low reps for fast-twitch dominant (endurance) muscle tissue?

Just curious.

Fast twitch fibers are supposed to be trained with higher load and less reps to take advantage of what they do best. I think you have fast and slow twitch fibers mixed up. Fast twitch are white and are the more explosive.

And yeah, a muscle’s role plays a part in determining your fiber make up. Your neck for instance; it’s primary purpose is holding your head up and moving your face around. While some may have more fast twitch muscles there, the neck has a lot of slow twitch fibers.

That being said everyone is different. So I am not saying it as a rule because even with necks I have read that some people have a lot of fast twitch muscle in their posterior neck (also read that is a good barometer for overall fast/slow twitch ratio). So I would say that the role of the muscle determines the propensity for the fiber make up.

[quote]Fezzik wrote:
Fast twitch fibers are supposed to be trained with higher load and less reps to take advantage of what they do best. I think you have fast and slow twitch fibers mixed up. Fast twitch are white and are the more explosive.
[/quote]

Ah, I knew someone would say that. I am aware of the fast/slow twitch nature of fibers and their INTENDED function, so my question was: what if you shocked the fibers with a stimulus they are NOT best-suited for? That was my question.

Thanks for the response.

I think that if you did high reps low weight instead of shocking the fast twitch fibers, you would just be using the slow twitch fibers within that muscle. Just a theory though

Heavy weight recruits all your muscle fibers - fast and slow. For bodybuilding, medium to heavy weights are generally used. Lift these weights and eat a lot of food every single day and good things will come.

I believe this is the premise of P/RR/S training. Different loads recruit different muscle fibers. Granted, heavy loads will recruit all, but fast twitch are the primary targets.

Also, very few people have a high percentage of fast or slow twitch. Most have a high type II, or intermediate, fiber type. These are variable and will actually change towards the stimulus presented to them. Obviously, we want higher loads so that these fibers mimic fast twitch, which have the highest potential for growth.

Training a predominantly fast twitch muscle, like a slow twitch muscle (ie reps beyond 15) would work as a tool to change things up every once in a while. DeFranco actually uses max repetitions for one exercise once per week (3 sets) in his WS4SB series. But as a primary tool, I think this idea is weak.

trenchant is right; your muscles will adapt to their training stimulus on a long enough time scale. Your IIa (medium) can act like IIb(fast) or I (slow) just like he said. You should try to take advantage of it by training slower muscles like fast!

In very slow twitch muscles, direct heavy training can be tough. I have read (Cressey/Robertson maybe?) that your abs, for instance, will plateau in about 6 weeks from that kind of training–that the best way to train them is increasing overall body strength through squats and deads etc. (If you only trained your abs DIRECTLY, they would plateau in 6 wks… your psoas/hip flexors can continue in strength gain, so it creates the illusion of increased ab strength)

Personally, I have found this to be true with my grip. Direct work sucks for making mine stronger, but it gets stronger as a byproduct of regular training.

Well the slow twitch fibres will be recruited with both light or heavy loads, but only fatigued (stimulated to adapt) through low weight/high rep training…
With high weight/low rep training the fast twitchers fatigue relatively quickly so the force you can produce drops off leading to failure,

Remember though, it’s the fast twitch fibres that are big and have the capacity to get real big and strong