Mike Mentzer caused those of us that could think, to actually think. I was doing up to 25 sets per body part when Mentzer came on the scene.I tried H.I.T. for around a month or so but it didn't work well for me and I went back to high volume. I spent up to 5 hours a day in the gym. That sucked.
For the past few weeks I've been training H.I.T as he outlined it in his last book with the exception of the number of rest days. I don't get stronger every workout but I don't think that at this point in my life that is realistic unless you're on a bunch of AAS or just beginning weight training.
There are days I want to do a few more sets (and so far I've resisted doing that) and there are days when one working set is enough. Then there are days when I know I just need to rest. I warm up well enough for me. Sometimes two or four sets of very light movements and then I do my working set. I do use pre-exhaust on chest, back and shoulder training. Mike Mentzer gave bodybuilders a way out of the gym. Training all the time is just plain ignorant and a waste of one's life. Exercise should add to your life, not detract from it and Mike was right about that aspect.
I think that drugs (which he freely admitted to using) played a big role in his development but that's true of all "modern" bodybuilders. He managed to develop a superb physique using a variation on the theme laid down by Arthur Jones. The key is to find what works best for you. I will keep this up for as long as I find it challenging. I have thought of giving the original H.I.T. as espoused back in the late 70s another try. Regardless, I would rather be reasonably well built than an overblown drugger that lives to pose in front of a mirror.
There's more to life than a gym.