MIke Mentzer made it popular with the one-two set routine, resting one or two weeks, only four exercises, static-holds and so fourth, but I think it was all wrong.
Mike Mentzer never training HIT himself, more like Arnold did, except Arnold did more sets as he worked out five hours a day and resting on sundays. I think 1-2 sets to failure, isn`t gonna give any results, as I myself tried it for 2-3 years without results. I think always going to failure, is another bad things, it only strains the nervous-system and not the muscles.
You don`t need to rest a week or two ether, as a muscle can be trained everyday. My best gains was from working out the same muscles everyday actually. The only positive thing with HIT is the reps, I think, like 8-15 for upper body, I tend to lean towards more reps myself as it builds more endurance and makes the blood circulate to build muscles, I tend to do more reps on legs also as it hurts more; you have to be a little uncomfortable to build muscles.
You can build muscles doing the same everyday mostly, but theres no problem with varying the exercises, as its more fun, youll avoid being stiff more also when you vary the exercises. Another problem with HIT is static-holds and eccentrics, it doesnt really build strength, only positive lifting does. Yes, I tried doing statics and eccentrics alot, but when you go back to lifting again, you have no strengt. It only works on paper.
I think Mike Mentzer was going a little mad in the end, he argued with Arnold alot also, even though he never practised what he taught. In my opinion, avoid HIT at all costs, it simply doesnt work. You have this slow rep-cadence also, 4 second down, 2 seconds hold and 4 seconds lift, but again, you build no explosive strenght, you dont use your muscle-fibers explosively, hence you don`t use all of them