Detecting overtraining with ACWR

What it is

ACWR (Acute:Chronic Workload Ratio) compares the load of the last 7 days to the average load of the last 28 days. It's one of the most used indicators in elite sport to anticipate overuse injuries. Reference: Gabbett (2016), The training-injury prevention paradox, British Journal of Sports Medicine.

How it's calculated

Formula: ACWR = acute load (7d) / chronic load (28d). Both loads are expressed in sRPE AU (see Understanding training load). Unbrokn computes ACWR per athlete per day and shows it in the Evolution tab.

Risk zones

• ACWR < 0.8: undertraining. The athlete is below their recent baseline. Detraining risk.
• 0.8 - 1.3: optimal zone. Load progresses in line with the baseline. Lowest injury risk.
• 1.3 - 1.5: caution. Load is accelerating faster than the baseline. Slow down or recalibrate.
• > 1.5: risk zone. Gabbett's studies show injury risk 2 to 4 times higher than the optimal zone. Reduce volume within 48 hours.

How to use it

ACWR doesn't replace your coaching judgment, it's a signal. Three typical cases:

• Return from pause or injury: chronic load has dropped to near zero. A single big session can spike ACWR to 3 or 4. Ramp up gently over 2 to 3 weeks.
• Competition prep: targeting a peak. Over the last 2 to 3 weeks, ACWR can climb to 1.4 - 1.5 if you know what you're doing. Beyond that, you're taking a risk.
• Volume phase: on a long cycle, keep ACWR between 1.0 and 1.3. If it climbs too fast, program a deload.

Where it shows up

Athlete profile, Evolution tab, Acute:Chronic Workload Ratio card. The number is plotted over 12 weeks with the colored zones in the background. If the athlete enters the risk zone (> 1.5), they show up in Athletes to watch on your dashboard.

Known limits

ACWR is a population tool, not an individual prediction. It works better on athletes with at least 4 weeks of history. Ignore it for the first few weeks after enrollment: chronic load isn't representative. Always cross ACWR with the athlete's feel and wellness score.

Sources

• Gabbett TJ. (2016). The training-injury prevention paradox: should athletes be training smarter and harder? BJSM, 50(5), 273-280.
• Hulin BT et al. (2016). The acute:chronic workload ratio predicts injury. BJSM, 50(4), 231-236.