I remember a reference in an article that mentioned this percentage. I can’t find it though. I think it was mentioned that at 80 - 85?
Does anyone recall that number or that article?
That’s not exactly accurate.
Muscle fibers are recruited depending on the requirement for force production.
When the fibers need to produce a low amount of force, let’s say 50% or less of your potential only the slow-twitch fibers will come into play.
As the need to produce more force increases you will need to bring in more fibers until at around 80-85% where you are recruiting most of the recruitable fibers.
From that point on, further force production will come from an increase in the firing rate of the muscle fibers (mostly fast-twitch fibers).
NOW two important points:
-
The 80-85% doesn’t necessarily refers to 80-85% of you maximum on an exercise. It refers to 80-85% of the amount of force your muscles can produce. While it can be correlated, it is not necessarily a cause an effect thing. For example if you have 60% of your maximum on the bar but lift it as violently explosive as you can, you might produce close to 100% of your maximum force potential (Force = Mass x Acceleration).
-
During a set, the relative percentage of force production increases as fatigue sets in. For example, let’s say that you have 70% of your maximum on the bar. Let’s say for the sake of argument that you are producing around 70% of your force potential to do the first repettition. Well, because you are creating fatigue from rep to rep you are also getting weaker from rep to rep. So the weight on the bar might be 70% of your force potential on the first repetition but by rep number 5 is will be around 80% of your maximum force potential at the beginning of the rep.
So you cannot. say that you recruit the fast-twitch fibers starting a weight that is 80% of your maximum or that with a weight that is 60-70% of your maximum you can’t recruit the fast-twitch fibers.
4 Likes