Tracking every hamstring has not stopped them tearing

Wearable data has given clubs enormous detail about muscle load without changing the decision that causes most injuries.

Every player at a serious club wears a vest with a tracker in it. The staff know his top speed, his accelerations, his decelerations, his high-intensity distance broken into bands, and how all of it compares with his rolling four-week average. And the injuries keep coming, at roughly the rate they always did.

That should bother people more than it does. The implicit promise of all this measurement was prevention. What it has actually delivered is explanation, which is a different product. After the hamstring goes, the data tells you a story about the three weeks before it. Before the hamstring goes, the same data mostly tells you the player is training normally.

Part of the reason is that the causal chain is short and violent. A muscle tears during a specific sprint, at a specific stride, usually while decelerating or reaching. What the tracker measures is accumulated load over days. Predicting a discrete event from a smoothed average is hard in any field, and it is especially hard when the base rate is low and the tolerable false-positive rate is nearly zero. Tell a manager to rest a fit-looking starter on a Saturday because a number went amber and you will be ignored, correctly, most of the time.

The other reason is more uncomfortable. The decision that causes injuries is usually not a training decision at all. It is a selection decision, taken by someone whose job depends on the next result, about a player who says he feels fine. No amount of telemetry changes the incentive there. The sports science department can produce a red flag and still watch the player start, because the alternative is explaining a defeat.

I am not arguing the data is worthless. It has clearly improved return-to-play protocols, where the question is concrete and the timeline is long enough for measurement to help. Knowing whether a recovering player has reached his previous top speed is genuinely useful, and clubs get that right far more often than they used to.

But we should stop describing load monitoring as injury prevention. It is load description. Prevention would require somebody to act on it against their own short-term interest, repeatedly, in public.

Until the person picking the team is also the person judged on availability in April, the vests will keep recording beautifully detailed accounts of injuries nobody stopped.