Even if you do the same total amount of lifting, going all the way to failure still makes you more tired than stopping short — so it’s not just how much you lift, but how hard you feel you’re working and how often you’re pushing that matters more.

If you lift weights until you can’t do another rep versus stopping before failure—while doing the same total amount of work—you’ll feel more tired and more worn out during the workout, especially if you’re a regular gym-goer.

If you lift weights until you literally can't do another rep, you'll feel more tired right after than if you stop a couple reps before failure — even if you're someone who regularly lifts weights.

Lifting weights until you can't do another rep leaves you much more tired during and after the workout than stopping a few reps short — even if both methods build muscle equally.

To test if rest time matters, researchers made sure both groups did the exact same amount of total lifting—so any differences (or lack of them) must be due to rest time, not how much they lifted.

When you lift light weights until you can't go on or until you slow down, your muscles swell and your blood gets more acidic in the same way — meaning your body reacts similarly to both methods.