When you lift weights until you can't anymore, you build about the same muscle size no matter how many reps you do, but doing more reps makes you stronger than doing fewer reps.

If you push your muscles as hard as you can until you can't do any more reps, that's what really makes them grow bigger. It doesn't matter how many reps you do, as long as you're giving your absolute best effort.

When you lift weights until you can't anymore, you build similar muscle size no matter how heavy the weights are, but lifting heavier weights makes you stronger and faster at moving them than lighter weights.

When people who are already fit push themselves as hard as they can during weight training, it doesn't matter if they lift heavy weights for a few reps or lighter weights for many reps—both ways build muscle about the same.

Going all the way to exhaustion on every set probably doesn't build more muscle than stopping a few reps short — both seem to work about the same.

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.