The limp outlives the injury that caused it

Protective movement patterns learned during pain persist long after the tissue has healed, and they redistribute load somewhere new.

Pain teaches quickly. Within a couple of steps of a bad ankle, an athlete has already worked out a way to walk that hurts less, and that solution gets stored. The tissue heals in six weeks. The solution can still be there six months later, running quietly underneath everything they do.

The adjustment is not one thing. Contact time shortens on the painful side. The hip does more, or less, depending on where the pain sits. Trunk lean changes to move the centre of mass over the sore limb or away from it. Muscles around the area co-contract more, stiffening the region, which reduces the demand on any single structure and increases the compressive load on the joint overall. All of it is sensible while there is something to protect.

The problem is that the nervous system has no reliable way of knowing when the protection can be retired. Pain resolves before confidence does, and confidence resolves before the motor pattern does, if it ever does on its own. So the athlete returns to full training with an asymmetry nobody has flagged, because it is too small to see and they no longer feel anything.

Load has to go somewhere. A leg that takes less on landing means the other leg takes more, every landing, all season. That is the mechanism behind the pattern where a hamstring injury is followed months later by a calf problem on the opposite side, or a groin, or a back that starts to complain in a way that has no local explanation. Chase the sore tissue and you are treating the symptom of a movement habit formed a year earlier.

There is also an inhibition component that is genuinely involuntary. Swelling in a knee reduces quadriceps activation reflexively, and the reduction outlasts the swelling. You can be as motivated as you like and still not fully switch the muscle on.

I think this is the strongest case for keeping an eye on athletes for months after they are declared fit, and it is the least funded part of any medical department, because nobody gets credit for supervising a healthy person.

The injury ends when the tissue heals. The movement it taught does not have an end date, and it will keep sending the bill somewhere until someone goes looking for it.