ACWR: Acute:Chronic Workload Ratio Explained

Key takeaways

• Acute = last 7 days; Chronic = 28-day EWMA
• Sweet spot: 0.8–1.3; danger zone: >1.5
• EWMA is preferred over simple rolling averages
• sRPE (minutes × RPE) is the most common load input
• Always combine with wellness and performance markers
• Use it as a traffic light, not a diagnostic

What is the Acute:Chronic Workload Ratio?

Acute:Chronic Workload Ratio (ACWR) compares an athlete's acute load (typically the last 7 days of training) to their chronic load (typically the trailing 28-day rolling average). The output is a single number — usually between 0.5 and 2.0 — that gives coaches a fast read on whether a recent training spike has outpaced what the athlete is prepared for.

It was popularised by Tim Gabbett and colleagues in rugby, AFL and cricket in the mid-2010s. Their headline finding: athletes who repeatedly produced ACWR values above ~1.5 had significantly higher rates of soft-tissue injury in the following week compared with athletes who kept the ratio between 0.8 and 1.3 — the now-famous "sweet spot".

ACWR is widely used in team sports, S&C and endurance coaching as a load-management traffic light. It is not a diagnostic — it tells you when to look closer, not what is wrong.

How do you calculate ACWR?

Step 1 — pick a load metric. Most coaches use session-RPE (sRPE = session minutes × session RPE 1–10), measured in arbitrary units (AU). GPS distance, total tonnage and high-speed-running metres also work; use whichever is consistent across the squad.

Step 2 — calculate acute load. Sum the last 7 days of daily load.

Step 3 — calculate chronic load. Average the daily load across the last 28 days (4 weeks). Best practice uses an Exponentially Weighted Moving Average (EWMA) rather than a simple rolling mean. EWMA gives more weight to recent days and avoids the "stale chronic" problem that pushes the ratio artificially high when an athlete returns from a layoff.

Step 4 — divide: ACWR = acute ÷ chronic. Track it daily. The number you act on is the trend over 3–5 days, not a single spike.

ACWR sweet spot and danger zones

ACWR < 0.8 — Undertrained. The athlete may be detraining, returning from illness or under-prepared for the demands of the next phase. Risk on return to full load is elevated, not because of fatigue but because of insufficient preparation.

ACWR 0.8–1.3 — Sweet spot. Appropriate progression with manageable fatigue. Most healthy in-season weeks should sit here.

ACWR 1.3–1.5 — Caution. A meaningful load spike. Tighten wellness monitoring (sleep, soreness, mood), watch for technical breakdowns and consider capping the next 2–3 sessions.

ACWR > 1.5 — Elevated injury risk. Strongly consider a deload, drop one session, or substitute high-impact work for lower-impact volume. This is the zone where Gabbett's data showed injury incidence rising sharply.

EWMA vs rolling-average ACWR

The original rolling-average (RA) method weights every day in the 28-day window equally. EWMA applies an exponential decay factor (λ ≈ 2/(N+1)) so yesterday counts more than 27 days ago. In practice this matters most in two situations: (1) when an athlete returns from injury and the rolling chronic is still inflated by their pre-injury baseline, and (2) when chronic load is genuinely climbing across the block and the rolling average lags the truth.

EWMA tends to flag spikes earlier and is the method most current research recommends. Elite Coaching Hub uses EWMA by default with a 7-day acute window and a 28-day chronic window — the standard Gabbett configuration.

Limitations and common mistakes

ACWR is correlational, not causal. The original injury-prediction claims have been challenged on statistical grounds (notably by Impellizzeri et al.). Treat ACWR as one of several risk markers — not a diagnostic and not a substitute for clinical screening.

Garbage in, garbage out. ACWR is only as good as the daily load data feeding it. Inconsistent session-RPE collection (athletes guessing the next morning instead of 30 minutes after the session) destroys the signal.

Don't game the number. Athletes who chase a "good" ACWR by adding junk volume on light days defeat the point. The ratio should reflect prescribed training, not be artificially smoothed.

Pair with subjective wellness (sleep, soreness, mood, stress on a 1–5 scale) and objective markers (jump height, HRV, grip strength). A rising ACWR alongside falling wellness scores is the actionable combination — either alone is noise.

How to use ACWR in S&C and team sport

In team sport, the Monday/Tuesday post-match window is when ACWR matters most. Players who finished match day with a spike already in the orange need protected midweek sessions before the next game.

In individual S&C, ACWR is most useful across a meso-cycle (4–6 weeks). A planned accumulation block will naturally push the ratio toward 1.3–1.5; the deload pulls it back to 0.8–1.0. If the accumulation block isn't pushing the ratio up, the loads aren't actually progressive — the metric becomes a sanity check on programming intent.

For return-to-play, ACWR is the headline metric in a graded return-to-running or return-to-sport progression. Most clinical pathways aim to keep weekly load increases at <10% and the ratio at 1.0–1.3 throughout the build-back.