Lifting weights until you can't do any more reps, whether with light or heavy weights, makes muscles grow bigger in fit young men after 8 weeks. It shows that pushing to your limit is what really matters for growth, not how heavy the weights are.

If you're already someone who lifts weights, doing light weights twice a week until you can't do more reps can make your muscles bigger and stronger in just 8 weeks.

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.

If you lift weights until you can’t do another rep—whether you use heavy weights or light ones—you’ll end up with about the same muscle growth after nine weeks, as long as you’re putting in the same effort and number of reps.

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.

You can get stronger and bigger muscles by lifting light weights until you're exhausted — even if you never lift heavy, which challenges the old idea that heavy weights are required.