The last rep of a set is a different exercise from the first

As a set approaches failure the load stops changing but almost everything about how the body produces it does.

Same bar. Same weight. Same movement written in the same notebook. And yet rep one and rep eight are two different physical events, which is why arguments about training to failure so often end up with both sides being right about different things.

Start with recruitment. Early in a set, at a submaximal load, the smaller and more fatigue-resistant motor units do the work. As they tire, force output would fall unless the system recruits progressively larger units, so it does, and by the final repetitions the biggest, fastest, most trainable fibres are finally involved. That is the argument for taking sets close to failure. Those fibres do not answer the phone unless the load is heavy or the set is long enough to make a light load behave like a heavy one.

Now the cost side. Bar speed collapses in those last reps even though intent is maximal, so time under tension rises while power falls. Metabolites accumulate, which reduces the muscle's ability to handle calcium and blunts force further. Technique drifts, and drift is not random. It moves toward whichever compensation is available, which usually means a segment that is not the target taking a share of the load at an angle it does not like. The lower back in a squat. The shoulder rolling forward in a press.

Fatigue also outlasts the set by more than people budget for. Peripheral fatigue clears reasonably quickly. The central component, the reduced drive that shows up as a lower voluntary activation, can persist for a day or two after genuinely maximal work, and it does not stay in the muscle you trained. It reduces what you bring to the next session.

My position is that failure is a tool with a narrow application, and it is the single most overused tool in strength training. It buys recruitment. It costs quality on every subsequent set that day and often on the next session too.

Stopping two reps short gets most of the recruitment for a fraction of the fatigue.

The last rep feels like the one that did the work. Feeling is not a good measure of what a muscle received.