There's a particular kind of squat frustration: you've done the work, the cues are grooved, and rep one proves it — deep, tall, controlled, a squat you'd frame. Then rep four arrives a little quicker, rep five turns around a little higher with the knees pinching in, and rep six is a different exercise entirely. The tempting diagnosis is "my form needs work." Look again. Your form is right there in rep one. What needs work is knowing when to stop.

Fatigue drift is a pattern, not a moral failing

Every quality in a squat is held by muscles that tire — including the small, unglamorous ones holding your trunk shape and steering your knee lane. As a set progresses, the body starts shopping for cheaper mechanics: descents speed up (control costs energy), depth creeps shallower, knees drift inward, the chest starts dipping first. None of this means you lack technique. It means technique has a fuel gauge, and you drove past empty.

The catch: from inside a hard set, you can't feel the drift. Effort is loud and form is quiet — rep five feels like rep one with more grit, which is precisely why lifters keep grinding reps their pattern stopped signing off on. The drift only shows from outside. That's a camera's job.

Reading the drift on video

Film a full set — side-on or front-on, whole body in frame — and two of CoachVision's reads speak directly to fatigue:

  • Rep evenness. The app scores how consistently your reps repeat across the set. A set on one clock scores high; a set where the later reps run on different timing — quicker drops, rushed turnarounds, longer grinds — frays the score. Scatter arriving late in a set is fatigue's signature, as distinct from scatter everywhere, which is usually a control story.
  • First bottom versus last bottom. Among the keyframes the app pulls is the last rep's bottom position, precisely so it can sit next to your representative rep's bottom. Same shape in both frames: the set was the right length. Higher hips, folded chest, or knees inside the ankles in the final frame: the set outlived the pattern, and now you know by exactly how much.

That comparison answers the only question that matters here — not "is my form good?" but "for how many reps is my form good?"

The rule and the drill

The rule: end the set while the pattern still holds. One rep in the tank, always — the rep you don't do costs you almost nothing in stimulus and saves you from rehearsing your worst mechanics at your most tired moment. Whatever you repeat under fatigue is what your body files as the movement. Make sure it's filing the good one.

The drill — 3-1-1 Tempo Squats: three seconds down, one-second pause, one second up, 3 sets of 5, light. Tempo work extends your pattern's endurance at the source — it trains the controlling muscles to hold shape longer — and its metronome carries over: sets practiced on a strict clock drift later and less.

Then re-test: film your normal working set weekly and watch two things move — the evenness score climbing, and the last-bottom frame looking more and more like the first. When rep five finally looks like rep one, add the sixth. That's earned volume — the only kind that builds what you're actually trying to build.