When people lift weights until they can't complete another rep, they experience more immediate fatigue—measured by fewer reps and slower movement—than when they stop a few reps short of failure.

When people lift weights until they can no longer complete another repetition, they experience more immediate fatigue—measured by fewer reps and slower movement—than when they stop lifting a few reps before failure.

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.

When people lift weights until they can no longer complete another repetition, they experience more short-term muscle fatigue than when they stop a few reps before failure, as shown by slower movement speed and fewer repetitions completed over eight weeks of leg press and leg extension exercises.

For people who regularly lift weights, training until they can't complete another repetition leads to the same increase in quadriceps muscle size as training that stops 1-2 repetitions before failure, even though the failure condition causes more short-term muscle fatigue.

Going all the way to muscle failure during weight training makes you way more tired—both mentally and physically—but doesn’t help you build more muscle than stopping just short, so it might not be worth the extra effort.