If you're already fit and lift weights, doing 5 to 20 sets of exercises for each muscle group every week won't make you grow bigger muscles any more or less than any other number in that range.

If you're a guy who already works out regularly, doing 5, 10, 15, or even 20 sets of exercises per muscle group each week won't make your muscles grow any bigger than the others—after 6 months, they all end up looking about the same.

Even though guys doing drop sets did only one set instead of three, their muscles grew just as much or more than those who did three sets.

Even though the guys doing the most workouts looked like they might have grown a little more, the difference wasn’t big enough to say for sure that more sets = more muscle.

If you're already experienced with weight training, doing 5 to 10 sets per muscle group each week builds just as much muscle and strength as doing 15 to 20 sets—so going over 10 sets won't give you extra gains.

If a young, healthy man lifts weights for 8 weeks, his muscles will likely get bigger—by about 6%, give or take a little.