something i have read about and put to use for great size gains are called "x reps" they are a bit complicated but...lets take a set of dumbell bench press: your on the bench with the weights in the air at the beginning, you bring them down to your chest, and then explode half a rep, quickly bring them back down and then perform a full rep. this counts as one. the idea is to perform semi-stretched reps in between the full ones and i find that it burns my muscles out very well when the weights are not quite heavy enough, as my gym only goes to 100lb dumbells too. they can be performed really with any exercise, i have seen the most growth caused by them while doing shrugs but lots in the chest and lats as well.