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.

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 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 young men lift light weights with very short breaks between sets for 8 weeks, their upper arms grow more than if they lift heavy weights with long breaks—even if they do the same total amount of lifting—because the short breaks create more muscle-burning stress that helps muscles grow bigger.

If healthy guys between 18 and 40 lift weights regularly for at least two weeks up to a year, they typically gain about 1.5 kilograms of muscle—no matter what kind of weight routine they follow.

The lower part of the thigh doesn't get noticeably bigger after 8 weeks of any of these training styles, even if the upper and middle parts do—meaning muscles don't grow evenly everywhere.