I've contemplated this for a long while and googled to my hearts content but still have not found a solid answer to this question. It's probably more opinion than anything, but there has to be some science or something on this topic.

At the end of my workout, how do I know I'm really done? What I mean is, after my squats, bench, row, and some accessory lifts to or just short of failure, by my program, I'm done. BUT, in 10 - 30 minutes I feel like I could get back in the rack and run though the routine again. Most likely with less weight but my concern is, if I can continue to break down those muscle fibers, why shouldn't I?

For instance, what if I finished my routine, dropped the weight and ran through it again with the same level of intnesity (failure or near failure on the same sets/reps as before) and so on until I either pass out or strip all the weight? Overtraining obviously, but that's one extreme. The other extreme would be not lifting anything at all I guess, so is 5 sets of 5 once time through the middle ground for any reason than it works for certain people?

Obviously more muscle damage, more rest required for repair. And, I don't have a source but I believe more frequent stimulation, more growth, as opposed to intense stimulation less frequently less growth.

I'm doing a variation of MadCow's progressive 5x5, so the reps are low and the weight is high. I know from experience the muscle fatigue seems to last longer when I do higher rep lower weight work but I also seem to grow better using higher weight, lower rep.

When I'm in the rack, I'm not fucking around, I'm pushing with all I've got and hit 80-100% failure on my heavy set every time. I add weight each week so it appears there is growth/strength gains happening but I HATE getting to work and feeling like I didn't workout earlier that morning.