I'm going to make this as brief as possible, while yet still making sure to include all the rational behind the way I train.
First of all, I follow very closely to what Mike Mentzer advocated in Heavy Duty II, though I admit I do some irrational things based on my own physical desires in the gym. I know I would do better if I followed directly as he advocated, but I do some things differently, basically for my own enjoyment in the gym.
You may notice I explain some things very closely to how Mentzer did. I'm sorry for that, but if
one man says it so perfectly, it's hard to rationalize it better. If we approach
muscle growth as a science (as it should be), we would first note that skeletal muscle grows solely out of function. In
other words, muscle only grows in order to lessen a stress on the body. Muscle only grows out of function, not for some sort of cosmetic purpose.
So what does that mean? It means, muscle only grows to become stronger so that added stress does not impede the body's homeostasis so deeply. If you think muscle grows for
other reasons, you really need to do some studying into physiology.
Getting to the point; the only thing that causes
muscle growth, is the
intensity of effort put forth. You can talk all you want about micro-trauma, but you are talking the equivalent of calculus, when you don't have a keen grasp on addition. I can go in depth as well as anyone on the physiology of skeletal muscle, but you must understand the basics of rational training, before getting into the "calculus" of
muscle growth.
Ok, so
intensity is the key to growth...what does that mean? Let's look at a barbell curl. Let's say you can do 10reps with a 100lbs barbell. If every time you worked biceps, you did 10reps with 100lbs, never attempting to do 11, do you think you would ever grow? Of course not, because you've not given your body a reason to adapt (grow). It can already tolerate that level of stress. The only way to cause growth, is to increase the stress on the body further then it can tolerate. The only way to increase that stress and push the body beyond normal limits, is to train to muscular failure.
Now comes the question, well how often and how much do I have to do that. Answer: far less then everyone suggests. Anyone who suggests that you must do more then
one set to properly stimulate growth is talking purely out of their ass(pardon the expression). Ask anyone that recommends more then
one set to failure, and you will never get a rational answer. Go ahead and ask a physical therapist, exercise scientist, MD, anyone you want and truly think about the answer they provide. It is always blind guessing with little rational behind it whatsoever. I can almost quote verbatim how most "experts" respond to the statement that
one set to failure is all that is required to stimulate maximal
muscle growth.
Ok, so now I'm only doing
one set to absolute muscular failure, how often do I have to do that? The precise amount that is necessary to allow for full recovery and full growth potential. Remember, muscle grows purely out of function, so the only reason muscle grows is to make an impedance of stress seem, well, less stressful. So, believe it or not, you should be stronger every time you enter the gym. If you enter the gym and you are not stronger then your last workout, you either did not allow enough time for recovery and growth and are over-trained, you did not meet your needs nutritionally (least likely to be true), or you did not train intensely enough to stimulate growth during your workout.
Another thing to keep in mind, is that
intensity and volume are INVERSLY proportional. In
other words, the longer you do something, the less intense you can make it. If you disagree, I suggest you study some physics. An example; giving it your all for both events, a 100 meter sprint is much more intense then a 2 mile run. That is a physical fact that no
one can deny, provided they are rational human-beings. "I cannot explain the actions of irrational people."- Mike Mentzer. Just look at the leg development of a sprinter compared to that of a distance runner. That immense
muscle growth is caused by the short burst of very intense work put forth by the sprinter.
The only reason people still advocate more then
one set is because of tradition. There is absolutely no science behind it. It is and always has been strictly tradition, even in the "exercise science" field. It is not science, it is tradition. People tend to have an extremely hard time accepting the fact that more then
one set is not needed because it goes against everything they have ever been told, even by self-proclaimed "experts" and "scientists".
More work is not better, less work is not better, but the precise amount that nature requires is what is best and will give you the fastest results. Please feel free to ask questions, but please, think deeply about your replies and questions. I know I'm cutting this short, but I only have so much time. I'm willing to answer as many questions as I have time for.
Train hard. Rest well.