Acute/Chronic Load Ratio : What the Research Actually Says

The acute/chronic workload ratio (often shortened to "ACWR" in the literature) is presented by many tracking tools as an injury-risk indicator. That's not what recent research shows. This article, part of the athlete tracking guide for sports coaches, details what the ratio actually measures, why its link to injury has been widely challenged since 2018, and how to use it honestly in your tracking.

What is the acute/chronic load ratio?

The ratio is calculated by dividing acute load (a 7-day rolling average) by chronic load (a 28-day rolling average). A ratio near 1 indicates recent load consistent with previous weeks; a high ratio indicates recent load well above the athlete's usual pattern.

See Calculate Training Load for the detail of how the underlying load itself is calculated.

Where the injury link came from

Popularized in professional sport in the mid-2010s, the acute/chronic ratio spread quickly as a prevention tool, on the idea that a ratio beyond a certain threshold (often cited around 1.5) would raise injury risk. That simple, easy-to-communicate idea was widely adopted in tracking tools, sometimes without questioning its scientific robustness.

What recent research challenges

The mathematical coupling problem

The classic ratio calculation includes the most recent week in both acute and chronic load, creating an artificial correlation between the two: a mathematical coupling that, on its own, can explain part of the observed relationship with injury, independent of any real physiological effect (Impellizzeri et al.).

Association isn't prediction

Several studies have found no solid evidence that the ratio can reliably predict injury : a Bayesian analysis found that a randomly generated chronic load produced "prediction" results comparable to the real ratio (study). Other work, in professional soccer players, found that ratio spikes and injury occurrence were dissociated over time (study). A statistical association, even when present in a given study, doesn't equal a usable predictive ability for any individual athlete.

So what is this ratio actually for?

The ratio keeps some value, as long as you change the goal : it isn't an injury-prediction tool, it's a load-variation indicator. A ratio climbing quickly simply signals that the athlete is training much more than usual. That's useful information for adjusting a program, independent of any claim about injury risk. That's why ProJump caps a generated program's projected load without ever presenting that cap as a guarantee against injury : it's a progression safeguard, not a medical forecast.

Using it reasonably

Watch the trend, not a precise threshold. A magic number like "1.5" has no solid grounding : it's the ratio's evolution over time that's informative, not its exact value at a given moment.

Cross-reference it with other signals. Athlete-reported effort, sleep quality, wellness questionnaire : the ratio is just one piece of the puzzle, never an automatic decision. See How to Rate Your Perceived Effort Well for the reliability of the RPE signal itself.

Never present it as injury risk. Not to the athlete, not in your own coaching language; the most honest framing stays "load variation" or "rapid progression."

See also Planning a Typical Training Week for building a progression that limits sharp load swings upfront, rather than correcting for them after the fact.