When people lift light weights until they can't anymore, their thigh muscles grow much more than if they just lift lightly without pushing to the limit, showing that working really hard is key for muscle growth even with light weights.

For beginners lifting weights, pushing muscles to complete exhaustion doesn't build more muscle than stopping just short of exhaustion, as long as the total amount of lifting is the same over 8 weeks.

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.

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.

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.

Lifting heavy weights and lifting lighter weights both build muscle about the same amount in healthy adults, as long as you do enough reps until you can't lift anymore.