If you're someone who's been lifting weights for a while, doing the same amount of heavy training over 9 weeks will make your thigh muscles grow by about half a centimeter — whether you spread your workouts over 2 or 4 days a week.

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.

Even if you do a lot of leg workouts, your thigh muscles grow about the same amount whether you do 20 or 50 sets a week—just doing any consistent training makes them bigger.

Lifting weights twice a week for six weeks — whether using heavier or lighter weights — helps young, healthy guys build leg muscle just about the same amount, compared to not training at all.

When people who already lift weights train with different methods—like starting light and going heavy, or doing sets to failure—all of them get about the same muscle growth if they do the same total amount of work.

Lifting weights more often each week helps you build more muscle—but only up to a point. After a certain amount, you don’t get much extra benefit, so there’s a sweet spot for the best results.