This is from a book I'm writing on programing for natural individuals.
STRENGTH-SKILL WORK DOESN’T HAVE THE SAME IMPACT ON CORTISOL…
A lot of studies have show that heavy work leads to a greater testosterone level than higher reps. In reality I don’t think that it’s because the heavy work raises testosterone that much more but rather because heavy work doesn’t raise cortisol as much as high volume work.
Cortisol is released during training mostly to mobilize stored energy to fuel muscle contraction. Specifically, it is raised when you need to mobilize glycogen and fat.
Higher rep work relies more on glycogen whereas heavier, lower reps work utilizes mostly the phosphagens for fuel. Phosphagen is the main source of energy for very intense contraction as long as it doesn’t last more than 12 seconds of so, after that the body switches to glycogen.
So if I’m using sets of 1-3 reps for example none of my sets will last over 12 seconds. And if I give sufficient rest between sets I can replenish the phosphagens before the next set. You are still using up some glycogen to restore the phosphagens, but still a lot of less then if you are doing higher reps.
As you can see strength-skill work (80-90% zone, not to failure) will not use up much muscle glycogen and as such you do not need to produce as much cortisol as during higher rep work (because cortisol is released to mobilize energy).
Now, cortisol and testosterone are fabricated from the same mother hormone (pregnenolone). The more cortisol you produce, the less material you have left to make testosterone.
Cortisol is the number 1 enemy of muscle growth in natural trainees; that’s why doing too much volume is a bad mistake. But with strength-skill work it is possible to do multiple sets (within reason) without jacking up cortisol.
Which is a good thing because strength-skill requires you to do many sets.
…BUT MAXIMUM EFFORT CAN HAVE A NEGATIVE IMPACT ON CORTISOL
A maximum effort causes psychological stress, especially when you are getting near 100%. That psychological stress can (will) increase the output of adrenalin and cortisol. Even though it doesn’t require a high mobilization of energy you are still getting the release in these stress hormones because of the intense psychological drain of training with maximum weights.
That’s one of the reasons why maximum effort work needs to be treated like volume for the natural trainee: don’t do too much of it or you will kill you gains or even regress.
So while you can do a fairly high amount of work when doing strength-skill work (80-90%, not to failure), you absolutely cannot do a high volume of work when training in the maximum effort zone (91-100%).
You can do at the most 4 lifts in the 90-100% zone in a workout devoted to that type of training. More than that and you are asking for trouble.