When young male athletes push themselves as hard as they can in weight training, whether using heavy or light weights, their muscles grow about the same amount after 8 weeks.

When young male athletes lift weights until they can't anymore, it doesn't matter much whether they use heavy weights or lighter ones—both ways build about the same amount of muscle after 8 weeks.

Whether you lift light weights with lots of reps or heavy weights with few reps—so long as you push until you can’t do another rep—you’ll build muscle about the same amount.

If you lift weights until you can’t do another rep, it doesn’t matter if you’re using light, medium, or heavy weights—you’ll still grow your muscles about the same, as long as you push yourself hard and do enough total work.

If you're lifting heavy weights and stop just before your muscles give out, you'll still gain about as much muscle as if you pushed to the very last rep you can possibly do.

Lifting heavy weights until you can't lift anymore makes young male athletes much stronger than lifting light weights over 8 weeks, even if both make muscles grow about the same size.