You DO NOT need to train to failure to stimulate muscular growth or strength.
I avoid training to momentary muscular failure like the plague lol. The only time I may hit real failure is when I am attempting a 1RM in a lift. That is the only time and I only try for max attempts every 6 months or so.
Good questions intraining.
This is the way I see it. If you know yourself well enough then you will know when you have done the last rep you can before the next which you will fail on. The last rep you can actually complete is where I always stop a set at.
If you incline press a weight for 6 reps 1 workout which is your target number of rep then add 2.5lbs-5lbs the next. Do as many reps as you can. You may only get 3 or 4 reps. You don't have to go to failure. The weight is heavier than the previous weight used and will stimulate new strength increases. If you wanted you might fail on teh 5th rep, but why? Just stop on the 4th rep. Next week try to get 5 reps etc. You don;t ahve to train to failure.
I don't EVEN come close to failure when I do squats. I do singles at about 85-90% of my 1RM most of the time for multiple singles and I am far from reaching failure on those single rep sets, but I get constantly stronger.
Seem confusing. I think the problem is many people are so stuck on training to failure they think it is the only way. It's not and imo it's not even the best way.
If you bench 225 for 10 reps 1 workout and that was your goal reps then you add 5lbs the next. Now, since the weight is heavier you will not get 10 full reps. You might be able to only get 6 full reps, where 7th would be the rep you fail on. Just don't do that 7th rep. The 6th rep is hard as it is without having to strain your ass off on that 7th magical rep, blah. You will ahve stimulated growth because you just lifted a heavier weight. You didn't go to failure, but scientifically the intensity level of that set of 230lbs was higher than the set of 225lbs even though you did less reps simply because the weight is heavier. That is as simple a way as I can explain.
Another great way to gain strength is to do lots of sets of low reps without training to failure. Like 10x3, 5x5(you don't have to go to failure on 5x5 either) 8x2, 6x1, 10x1, WHATEVER. Experiment.
I think in a way HIT training has done a big diservice to alot of people that lift because it has confused them on what it takes to stimulate muscular growth and size gains.
Scientifically speaking:Failure is not even a prerequisite for stimulating growth and strength increases.
Look at the majority of powerlifters and olympic weightlifters. They understand the principle of intensity and they rarely train to failure except when attempting 1 rep maxes in their basic lifts!
That's the best I can do as far as explaining this. I know their are guys on this board that can delve into it alot deeper and really show the scientific side of it better than I can.