For young guys who don't usually exercise, doing one set or three sets of heavy lifting doesn't make a big difference in muscle growth, but three sets might have a small, not-proven benefit.

The total amount of work done (weight × reps × sets) seems to matter for muscle growth — more work generally leads to more muscle, even if the weights are light.

Lifting heavy weights for fewer reps and lighter weights for more reps both build muscle about the same in young men when you push yourself to the max, showing that the total work done matters more than how heavy you lift.

Doing more sets at the gym than you're used to—like going from 18 to 33 sets a week per muscle group—doesn’t make your muscles grow significantly more, even though you might see a little more growth overall.

If you're a young man who already trains regularly, doing more sets with lighter weights for 6 weeks can make your thigh muscle grow a little bigger — but doing fewer sets with heavier weights won't make it grow at all.

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.