The tracking vest is mounted in the wrong place for the injuries we worry about

Trunk-mounted units measure the torso beautifully and tell you almost nothing about the joint that actually breaks down.

Between the shoulder blades. That is where the pod sits, and it sits there for practical reasons: it is comfortable, it holds still, the satellite fix is clean, and nobody has to convince a player to wear anything around his ankle. Everything the sports science department reports flows from that one location on the body.

Which is fine for distance and speed and reasonably honest for accelerations. It is close to useless for the thing that keeps players out for six weeks. Hamstrings tear during the swing phase of a sprint, at the hip and the knee, under a load the trunk barely registers. Ankles go in a single planted cut. A calf goes on the two hundredth push-off of a session, not the fastest one. The pod knows how quickly the middle of the body moved. It does not know what the far end of the leg did to make that happen.

You can see the gap in a specific case. Two players finish training with the same high-speed running total. One did it in long straight runs down a channel. The other did it in nine-yard bursts with a turn at both ends. Their reports are twins. Their tissue loads are not remotely alike, and the second player's Achilles has absorbed several times the braking work.

Some of that is patched by adding accelerometer counts and calling the sum a load score. I have never trusted those scores, and I would say the same in front of the people who build them. They are weighted sums of quantities in different units, tuned until the output looks plausible against last season's injury list, which is another way of saying they were fitted to noise. Change the pitch surface and the accelerometer counts drift. Change the shoe and they drift again.

The honest position is narrower and more useful. Use the vest for what it genuinely measures, which is volume and speed exposure, and stop pretending it measures risk. If you want joint load you need force plates on a Tuesday morning, and someone willing to compare this week's jump asymmetry against the player's own baseline rather than a squad average.

The best fitness coaches I have watched already work this way. They read the numbers for an hour and then go and watch the player walk to the car park.