You lose track of where the joint is before you lose the strength to hold it

Position sense degrades under fatigue earlier than force does, which is why the ankle rolls on a step nobody was watching.

Nobody sprains an ankle on the flat while paying attention. It happens on a landing where the foot met the ground half a degree off what the body expected, and the correction did not arrive. The muscles were strong enough. They simply did not know, quickly enough, that they were needed.

Joints report their own position through several channels at once. Muscle spindles sense length and the speed at which length changes. Golgi organs report tension. Receptors in the capsule and skin fill in the rest. That stream is what allows a peroneal muscle to begin resisting inversion before the ankle has rolled far enough to hurt anything, and the timing budget for that is tiny, somewhere in the region of a few tens of milliseconds.

Fatigue interferes with the stream rather than the muscle. Spindle sensitivity is modulated by the same nervous system that is tiring, accumulating metabolites alter receptor behaviour, and the athlete's estimate of where their limb sits drifts. Studies of joint repositioning after hard exercise show errors growing in the direction you would expect, and the athlete does not notice, because the corrupted signal is the only signal they have. Their sense of being fine is being generated by the thing that has degraded.

After an injury, the loss is structural as well. A sprain tears capsule and ligament, and those tissues carry receptors. The joint comes back with a thinner information supply permanently, which is a large part of why the strongest predictor of an ankle sprain remains a previous ankle sprain, long after strength and range have been restored.

What the system does instead is substitute vision. That works well in a gym and fails in a match, where the eyes are committed to a ball and an opponent and cannot be spared for the foot. I have seen athletes who balance beautifully in a clinic and roll an ankle in the first competitive session back, and the difference between those two situations is not their leg.

Which is my argument against balance work done in silence, on a mat, staring at a fixed point. It trains the compensation, not the deficit.

Make the athlete catch something. Make them look elsewhere at the moment the surface moves. That is the only version of the task where the joint has to answer on its own.