leglock

over the years ive noticed that as soon as i start training heavy i get either lower or upper back problems
now i know your probably going to say maybe i shouldnt be lifting at all,but i know its not a serious injury,and well its just the addiction and all that !
i get to a certain weight on exercises that i can lift reasonably easy for say 7 or 8 reps,but then need a week off for my back to come back to normal !
its nothing to do with bad form etc,just a crappy back from years ago.
what i want to know is basically this...is there any other way to bulk apart from going real heavy?...ive read about this pre exhaust stuff,is this the kind of thing i should be looking at?
any help will be much appreciated.