This i from an article posted on my thibarmy.com page:
"STRENGTH-SKILL WORK DOESN’T HAVE THE SAME IMPACT ON CORTISOL…
A lot of studies have shown that heavy work leads to a greater testosterone level than higher reps. In reality, I would more likely credit this to the fact that heavy work doesn’t raise cortisol levels as much as high volume work.
Cortisol is released during training mostly to mobilize stored energy to fuel muscle contraction. Specifically, it is released when you need to mobilize glycogen and fat. Since 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.
Higher rep work relies highly on glycogen whereas heavier, lower rep work utilizes mostly phosphagen for fuel. Phosphagen is the main source of energy for very intense contraction as long as it doesn’t last more than 12 seconds or so, after which the body switches to glycogen.
So let’s say for example that I am using sets of 1-3 reps. None of my sets will last over 12 seconds and if I allow sufficient rest between sets, I can replenish my phosphagen levels before the next set. Although some glycogen will still be used to restore the phosphagen levels, this will be at a much lesser extent than when using higher reps. Simply put, strength-skill work (80-90% zone, not to failure) will use less muscle glycogen, requiring you to produce less cortisol compared to higher rep work (because cortisol is released to mobilize energy).
As you can conclude, 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 approaching 100%. That psychological stress can (will) increase the output of adrenalin and cortisol. Even though training with heavy weights does not require a high mobilization of energy, it induces an intense psychological stress that will result in the release of these hormones.
That is 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 your gains and may even cause you to 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 train in the maximum effort zone (91-100%) at high volumes. At most, you should devote 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."
So in that regard the 5-4-3-2-1 method, which is still one of my favorites (along with the 3-2-1 waves method) , it is a perfectly good way to train if you are natural BUT the sets should not be a mast effort. So instead of ending the set of 1 with 100% I'd shoot for 90 or 92% most of the time.