What the ACWR is and what its limitations are

What it compares

The ACWR relates the current week’s load to the average of the last four. A value of 1 means this week matched the usual; below, less was done; above, more.

It is essentially a measure of change. It does not say whether the load is high or low in absolute terms: it says whether it differs from what that athlete had been doing. Two players with very different loads can share the same ratio, and the same player can have opposite ratios at two points in the season doing the same work.

How it is calculated

The most widespread version divides the load of the last seven days by the average of the last twenty-eight. It is called the coupled rolling-average method: coupled because the current week is also part of the denominator.

There is a second variant, the exponentially weighted moving average, which weights recent days more instead of treating all twenty-eight equally. On the same data, the two give different numbers. That alone should be enough to distrust any threshold presented as universal: the value depends on the method chosen to compute it.

Why it does not predict injuries

The ranges circulating as risk zones come from studies in specific populations: one sport, one competitive level, one calendar. Transferring them to any athlete assumes the relationship observed there holds everywhere, and that has not been established.

The methodology itself has been criticised in the scientific literature, particularly over how the denominator is constructed and over the statistical treatment of the load–injury relationship. This is not a marginal argument: it is part of an open debate in the field.

None of this makes the ratio useless. It makes it one signal among others, flagging that something changed — after which you still have to look, ask the athlete, and cross it with everything else being recorded.

How to use it without it using you

Three practical criteria. First: individual, not team. A squad average mixes the player who played ninety minutes with the one who never came on, and the result describes nobody.

Second: with at least four weeks of continuous logging. Before that the denominator is unstable and the ratio jumps for reasons unrelated to training.

Third: read it alongside the context. A high ratio in pre-season is the plan working; the same number mid-season, after a week of fixtures, is a different conversation.