Hello,
You advocate the idea that it’s beneficial to do exercises which permit a lot of volume with low fatigue, in order to build muscle mass.
I will take the knee extension VS squat comparison. I agree that the squat would be more fatiguing, and that more volume can be done with the knee extension exercise.
Question is, why is the knee extension less fatiguing, but not less effective?
If 3 sets if 8 reps @ 7 in the squat would be as fatiguing as 6 sets of 8 @ 7 at the knee extension, why would the knee extension be better in terms of hypertrophy?
Of course the question is not specifically about these two exercises, but in general - why would it be better to get the same amount of fatigue through more sets than less sets, considering the same rep range and same RPE.
You advocate the idea that it’s beneficial to do exercises which permit a lot of volume with low fatigue, in order to build muscle mass.
Not exactly:
There is a clear relationship between training volume and hypertrophy outcomes.
There is NOT a clear relationship between proximity to failure and hypertrophy outcomes (e.g., difference between a set at 75% 1RM taken to 2-3 RIR vs. 0 RIR).
Fatigue rises significantly (and likely disproportionately) as you approach failure (e.g., from 4 RIR to 3 to 2 to 1 to 0).
There is an obvious trade-off between fatigue and the amount of training volume someone can feasibly complete and recover/adapt to while avoiding overuse syndromes or other issues.
Therefore, it makes sense to set up training in order to maximize the stimulus per “unit” fatigue. We could do something extremely hard, once … or we could do something moderately hard, many times, and get a bigger net adaptation from training the thing many times.
I will take the knee extension VS squat comparison. I agree that the squat would be more fatiguing, and that more volume can be done with the knee extension exercise.
Question is, why is the knee extension less fatiguing, but not less effective? If 3 sets if 8 reps @ 7 in the squat would be as fatiguing as 6 sets of 8 @ 7 at the knee extension, why would the knee extension be better in terms of hypertrophy? in general - why would it be better to get the same amount of fatigue through more sets than less sets, considering the same rep range and same RPE.
Because fatigue does not equal hypertrophy, and because fatigue is not itself the desired outcome of our training.
Assuming your outcome of interest here is quadriceps hypertrophy (and given your assumption about equivalent overall fatigue between those two … which may not be true), the answer would be because you have done more total training volume with the leg extension.
If the outcome of interest is squat strength performance, then squatting would be the superior choice, particularly in the short-term (although there may be a role for leg extensions as a supplemental movement that training as well).
I wonder, what is the mechanism behind an activity which create higher / lower fatigue per “unit” of volume?
I mean, why is a 3RM squat more fatiguing than a 3RM knee extension, but doesen’t provide more stimulus?
why is a 3RM squat more fatiguing than a 3RM knee extension
I suspect you can figure this out.
but doesen’t provide more stimulus?
Assuming we’re limiting the discussion to quadriceps hypertrophy as the outcome here, both are using the target musculature for one set of 3 reps.
You could certainly argue that the squat is providing a greater whole-body stimulus since a much larger amount of musculature is involved, but again - this is coming with a significant fatigue cost, since you cannot do repeat sets of 3RM squats in order to amplify that stimulus in terms of training volume.
I can figure out why the squat is more fatiguing in terms of overall fatigue, but not in terms of quadriceps alone. If we limit the discussion to quadriceps hypertrophy (which we should, of course), than we also need to limit the discussion to quadriceps fatigue.
Will the knee extension be less fatiguing for the quadriceps but more stimulating, in a given dose? (relative to the squat)
There is a clear relationship between training volume and hypertrophy outcomes.
Shouldn’t this statement be qualified as: "There is a clear relationship between training volume and hypertrophy outcomes_, given that the training volume is_ at a high enough intensity to drive adaptation."?
There is NOT a clear relationship between proximity to failure and hypertrophy outcomes (e.g., difference between a set at 75% 1RM taken to 2-3 RIR vs. 0 RIR).
In one of the books you guys recommend–Strength is Specific by Chris Beardsley–he says that it is necessary to train to failure when using light or moderately heavy loads in order to achieve similar hypertrophy as compared to heavy loads not to failure. In his words:
When we lift a heavy load (<85-90% of maximum strength), we achieve maximal motor unit recruitment from the first repetition of a set, and there is no need to increase fatigue further in order to recruit more motor units. In addition, the bar speed is slow enough, because the force-velocity relationship means that sufficient mechanical loading is experienced by the working muscle fibers.
In contrast, when we lift light or only moderately-heavy loads, we do not achieve maximal motor unit recruitment from the first repetition of a set. Therefore fatigue is essential if we want to recruit the high threshold motor units that produce the necessary stimulus for muscle growth.
Therefore, training to failure is likely to be helpful only for enhancing muscle growth when lifting loads are lighter than approximately 85-90% of maximum strength, and not when using heavy loads.
What is the takeaway?
Training to failure can be used to increase motor unit recruitment when lifting light or moderately-heavy loads, which in turn increases the likelihood that the muscle fibers attached to high-threshold motor units will grow.
However, since heavy loads already achieve full motor unit recruitment, even without the onset of fatigue, it seems unlikely that training to failure will have any incremental benefit under those circumstances.
What are your thoughts on the idea that it is necessary to train to failure when using light or moderately heavy loads in order to achieve similar hypertrophy as compared to heavy loads not to failure?
