Whether you lift lighter weights or heavier weights until you can't do any more reps, both ways give you the same muscle growth and strength gains if you're already used to training.

This study shows that when young women lift weights until they can't anymore, it doesn't matter if they use light or heavy weights—both ways build muscle about the same.

If you're a young man who already lifts weights, doing workouts with either light weights (lots of reps) or heavy weights (fewer reps)—as long as you push yourself until you can't do another rep—will make your muscles grow just as much either way.

Lifting weights until you can't lift anymore makes muscles grow bigger no matter how heavy the weights are, but using heavier weights builds more strength than lighter ones.

If you're a young guy who already lifts weights, doing workouts until you can't do another rep for 12 weeks will make your legs and shoulders just as strong whether you use light or heavy weights—but for the bench press, heavy weights make you stronger than light ones.

When young women lift weights until they can't anymore, they do more total work with lighter weights than heavier ones, but this extra work doesn't make their muscles grow any more, showing that just doing more reps isn't what makes lifting effective.