Originally Posted by RickB
Well I think the body is adaptive in two ways.
1) Progression of weights - Lifting heavy and trying to keep moving up
2) Progression of reps - Stamina if you will, your body can do more reps if you push it.
I think both can build size. Maybe reps are more for tweaking/sculpting (?).
there are quite a few more progressions than this, but one thing i want to note here is that it is pointless to try for only one without the other.
If my max single in the squat is 400ibs, it is really hard to add 5ibs without making that my max triple for example. same thing goes for rep progression, eventually you will hit a point where in order to see a specific adaptation (i.e. growth/strength) you need to add weight, because there is a point in which your muscles will begin to change the adaptation, obviously if your max curl for 8 reps is 80ibs, your arms will look different than if you can do 100 curls with that 80ibs.