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Acute:chronic workload ratio, in plain English

By Dylan, founder of Tempo · 4 min read

Short answer: the acute:chronic workload ratio (ACWR) compares what you've done lately (the last ~7 days) to what your body is used to (the rolling ~28-day average). Acute ÷ chronic. Around 1.0 means this week looks like your recent normal; spike well above it — roughly past 1.5 — and injury risk tends to rise. It's a handy early-warning flag for "am I ramping too fast?" — but it's a guide, not a rule, and it can't see your sleep or your life.

What it's really saying

The idea is simple and intuitive: injuries cluster less around high training and more around sudden change in training. Your body adapts to the load it's been getting; pile on a lot more than that, quickly, and the tissues haven't caught up. The ACWR just puts a number on "how much more am I doing this week than I've been conditioned for?"

How it's calculated

Acute load = your training in roughly the last 7 days. Chronic load = your rolling average over roughly the last 28 days (your "fitness base"). The ratio is acute divided by chronic. "Load" can be weekly distance, or something effort-weighted like duration × intensity — the more it accounts for intensity, the better, since 10km of intervals isn't 10km of jogging.

The rough sweet spot

The often-cited zone is about 0.8–1.3, with risk tending to climb above ~1.5. Below ~0.8 you're detraining or tapering (sometimes exactly what you want). The classic ~10%-per-week build keeps you comfortably inside the band. But hold these numbers loosely — they're population averages from imperfect studies, not a personal speed limit, and the exact figures shift with how you measure load.

Why it's a guide, not a rule

The ACWR has had real academic pushback: the results depend heavily on calculation method, the "danger zone" isn't as crisp as early papers implied, and crucially the ratio is blind to everything off the road — sleep, work stress, nutrition, life. A 1.4 in a calm, well-slept week is a different animal from a 1.2 during a brutal work stretch on five hours' sleep. So it's best read as one voice among several: a prompt to look closer, not a verdict to obey.

How to actually use it

Treat a rising ratio as a question, not a command: "I've ramped faster than usual — is that deliberate, and does the rest of my life have room for it?" Sometimes the honest answer is "yes, planned build, feeling great, proceed." Sometimes it's "actually I'm fried, let me hold steady this week." The number sharpens the question. You still answer it.