The acute to chronic workload ratio is a fraction, not a diagnosis

A number built by dividing one rolling average by another will find danger zones even in data containing no injuries at all.

Divide this week's training load by the average of the last four weeks. If the answer sits much above one and a half, you are told, you are in the danger zone. This single fraction has shaped how a lot of squads plan, and I think it has been asked to carry far more weight than its construction can bear.

Start with the arithmetic. The numerator is inside the denominator. This week's load forms part of the four week average it is being compared against, so the two terms are mathematically coupled and the ratio behaves oddly in ways that have nothing to do with the athlete. Change the window lengths and the same training data produces different ratios and different alarming weeks. Nothing about the body changed. The window changed.

Then there is the denominator problem. An athlete returning from a lay off has a tiny chronic load, so any training at all produces a large ratio. The model flags them as high risk. They are also, in plain terms, unfit and detrained, which is a genuinely elevated risk state. So the model looks right for reasons unrelated to its logic, and that kind of accidental correctness is how a weak tool builds a reputation.

The deeper issue is what load means. It is usually minutes multiplied by a subjective effort rating, or distance, or some figure derived from a GPS unit. Those measures compress everything. A long steady run and a set of hard hill sprints can score the same and stress completely different tissue at completely different rates. Bone, tendon and muscle each respond to different features of the loading, and none of them respond to a weekly total.

I am not arguing against monitoring. I am arguing that the ratio has been treated as a threshold when it is at best a prompt to have a conversation, and that treating it as a threshold has real costs. Athletes who were fine get held back. Athletes quietly accumulating a bone stress injury pass the check because their totals looked smooth, and smooth totals were never the mechanism.

The things that would actually help are duller. Loading rate rather than volume. A record of surface and shoe. Sleep. An honest weekly answer to whether anything hurts.

None of that fits inside a single fraction, which is exactly why the fraction got popular.