T Nation

Fatigue Not Connected to Fiber Recruitment/Hypertrophy?

Just read an article in Breaking Muscle about the Journal of Strength & Conditioning recently releasing a study which showed a lack of additional fiber recruitment with fatigue, thereby questioning the connection to hypertrophy. Should this effect our approach to workouts, or are there other factors that supersede this? Anyone smarter than me (CT!) have insight on this? Thanks!

Maybe I sound condescending saying this, but I kinda thought that was common knowledge… that there’s no relationship between soreness or fatigue and hypertrophy. (It’s quite possible that’s not what you just said though and I completely misinterpreted.)

Soreness and fatigue come from a depletion of energy and accumulation of byproducts like H+ and Ca+. None of which have anything to do with the known mechanisms of hypertrophy.

My biochemistry sucks, but that’s been my understanding.

It may be condescending, but justly so. I just don’t have a firm grasp on the mechanisms for hypertrophy…

I think this is the portion that I couldn’t quite get my head around:

The researchers noted that one of the major take-away points from this study is the prescription of exercise based on percentages of 1RM. Using percentages might be the most common method that coaches use to dole out programs, but with such a huge variation in ability at the 75% of 1RM load used in this study, it may not be warranted. Even more significantly, the motor response to exercise was varied between the participants. With such a diverse group, a single percentage-based program like the one used could yield very different results.

What the researchers recommended instead is a repetition maximum approach. With this approach, a coach can simply prescribe a five rep max, ten rep max, and so on, rather than using a percentage of the one rep max. But even if you use this method, it seems that excessive fatigue doesn?t stimulate the muscular fibers any more in most people. If you?re looking for greater strength or size, this study suggests fatigue isn?t all that important of a factor.

I’ll admit near ignorance on the subject, but, this is how I’ve learned to understand it.

You have your fast twitch fibers that are quick and explosive, and your slow twitch fibers that are slower-moving and good for endurance. Different muscles have different proportions of these fibers. Now, of that, you have a certain amount of “neurological efficiency”, basically what percent of those fibers your nervous system can reasonably recruit, regardless of fiber type.

In order to get stronger, part of it is getting better at recruiting more fibers, and part of it is getting the fibers themselves “stronger”, which can include increasing the number of fibers. From a hypertrophy standpoint, your goal is to get the fibers “bigger”.

Macro-level view, and overly simplified.

But if you take that, and you take the idea that the body will adapt to the demands placed on it, you can then get to the various training methodologies.

If you focus only on heavy explosive movements, your body basically realizes that 1) you need to recruit more fast twitch fibers since you need it for short duration only, and 2) they need to be stronger. So in effect, you’re signalling the body to improve neurological efficiency – to stimulate more actual fibers – as well as to improve the performance of those fibers. From what I understand, the body is also capable of converting some slow-twitch fibers into fast-twitch fibers, again, in response to this kind of demand. I think the fast twitch fibers are physically larger and grow as they get stronger, at least compared to slow-twitch fibers. (I could be very wrong about that last point.)

If you focus only on heavy slower movements, you get the need for more fiber recruitment, overall, and more strength, overall. So you get improved neurological efficiency, as well as strength with both fast and slow twitch fiber makeup. Depending on your original makeup, you can have more slow strength from your slow-twitch-fibers, or faster strength. By training in a mix of rep ranges and speeds, you can improve the development of both types of fibers… and by a combination of exploding + grinding, maximally use that.

On the other hand, if you focus on more pump-based work, you end up flooding the cells and fibers with fluid and other metabolic byproducts, “stretching” things out, and sending a signal that at a cellular level, they’re simply not big enough. And the body compensates by making them bigger. Fiber types involved here depends on a mix of speed and intensity, but it’s not really about “fatigue” as much as it is about maximal accumulation of fluid and “other metabolic byproducts” (a term I’m using since I’m not sure of the exact compounds).

A secondary effect from this is that as the muscle fibers swell up, the capillaries are compressed and there’s an occlusion effect that signals that there’s not enough blood getting to the area. So the body, again, responds by improving the blood flow to the areas. That improved blood flow then allows more efficient nutrient delivery and improved healing.

And then on top of it all, there’s all sorts of neurological adaptations that can be produced by how you train.

This is my really really naive understanding of how it all works.

Forgot this piece.

With respect to fatigue, you have 3 basic energy systems used. Again, these adapt based on the demands you place on them. But if you notice from the above, none of those necessarily rely on any of the energy systems being depleted. You can work well within the specific energy system’s limits and produce those same results. For example, you can make a fist, flex your arm and do a few unweighted bicep curls, and the muscle cells will respond by getting a bit of a pump, but you’re still far away from actually being fatigued at all.

Cool thought on separating fatigue from “accumulating a bunch of stuff” with constant tension.

CT seems to be experimenting a lot with this so I’m eager to hear his take