I'm reading a most recent personal trainer text book. In it, they site a study that says that their is no difference in muscle gained by body builders who only perform one set vs. multiple sets. If I bench 200 pounds max, then there is no difference in the muscle I gain from 8 x 160 pounds once vs. 8 x 160 pounds, 3 times, with 60s rests. Then, without siting anything, they go on to recommend one set only for beginners and multiple sets for everyone else. What's the deal?