The Acute Chronic Workload Ratio (ACWR) is the most widely used method in sports science for monitoring training load and flagging injury risk before it happens. This guide covers what ACWR is, how to calculate it with the sRPE method, what the zones mean, and how to act on the numbers.
ACWR compares how much you trained recently (the acute load, typically the last 7 days) with what your body is adapted to (the chronic load, the rolling 28-day average). The ratio answers one question: is this week's workload appropriate for what I'm prepared for?
ACWR = Acute load (7 days) ÷ Chronic load (28-day average)
Session RPE (sRPE), validated by Carl Foster (1998), estimates internal training load without any hardware. Thirty minutes after a session, the athlete rates how hard it was on a 1–10 scale (RPE). Multiply by the session length in minutes:
Session load = Minutes × RPE
Example: 60 minutes at RPE 7 = 420 arbitrary units (AU)
No GPS vests, no heart-rate straps — which is why sRPE is the standard load-monitoring tool for team sports, running, CrossFit and strength training alike.
< 0.8Under-training
Load is well below what the athlete is adapted to. Fitness decays, and a sudden return to normal load often spikes the ratio into the danger zone.
0.8 – 1.3Sweet spot
Acute load matches what the body is prepared for. Fitness improves with minimal injury risk — this is where you want athletes week to week.
1.3 – 1.5Warning
Load is rising faster than the chronic baseline. Acceptable for a planned overload week, but repeated weeks here raise injury risk.
> 1.5Danger zone
A sharp spike versus the 4-week baseline. Research links sustained ratios above ~1.5 to a significantly higher likelihood of injury in the following days.
No. Recreational runners and gym-goers get injured from load spikes just like pros — they just have fewer people watching the numbers. A 10-second sRPE log after each session is all it takes.
One week captures the current training stimulus; four weeks approximate the fitness the body has adapted to. These windows are the most studied in the ACWR literature.
No — it's a risk signal, not a diagnosis. Use it alongside pain, sleep and soreness to make conservative adjustments. Sharp or worsening pain always warrants a professional.
Calculate your ACWR in 10 seconds
Free, no sign-up — log a session and see your zone instantly.