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What Is ACWR? Acute-to-Chronic Workload Ratio Explained
ACWR is a way of comparing how hard you've trained recently against what your body is used to. Used sensibly, it's a useful flag for "you ramped up too fast." Used dogmatically, it's been overstated. Here's the real version.
The basic idea
Your acute load is your recent training stress, usually the total of the last 7 days. Your chronic load is what you've adapted to over time. The acute-to-chronic workload ratio is simply one divided by the other:
"Load" can be tonnage (sets × reps × weight), or a session-RPE measure (how hard each session felt × its duration). The unit matters less than being consistent.
One detail worth getting right: the version above is the uncoupled ratio, where the most recent week is left out of the baseline it's compared against. The original "coupled" version folded the acute week into a 4-week average, which partly compares the week against itself, a mathematical artifact the literature has since flagged (Lolli et al., 2019; Windt and Gabbett, 2019). Ægir Iron computes the uncoupled version.
How to calculate ACWR: a worked example
Say you're a powerlifter tracking weekly tonnage. Over the three weeks before last you lifted 42,000, 45,000, and 39,000 lb, for a chronic baseline of 42,000 lb a week. Last week you pushed to 54,000 lb. Your ACWR is 54,000 ÷ 42,000 = 1.29: elevated, but exactly what the first week of an intensification block should look like. Nudge next week to 60,000 lb and the ratio climbs to 1.43, and now you're spiking on purpose rather than by accident. The arithmetic is deliberately simple, so the value is in watching the trend week to week, not chasing a decimal.
How to read the number
Read the zones as descriptions of your recent loading, not risk bands:
- ~0.8 to 1.3: steady, sustainable loading. You're progressing without a sharp jump.
- ~1.3 to 1.5: elevated. Load is climbing above your recent base, which is exactly what a planned intensification or peak looks like.
- Above ~1.5: a sharp spike relative to what you're used to. Do it on purpose or not at all.
- Below ~0.8: you're detraining or deloading. Sometimes intentional (a taper), sometimes a sign you've backed off too much.
Where it came from, and the caveat
The ratio was popularized by Tim Gabbett's work on athlete load management (Gabbett, 2016), largely in team sports, and was endorsed in the IOC's 2016 consensus statement on load and injury (Soligard et al., 2016). Then the science moved. Methodological reviews, most pointedly Impellizzeri and colleagues (2020), substantially dismantled the claim that specific ACWR zones predict injury, along with the U-shaped "sweet spot" risk curves built on the early studies. What survives is the arithmetic itself: a clean description of how your last week compares with the month behind it. So treat ACWR as a guardrail and a conversation-starter, never a precise injury predictor, because it isn't one.
ACWR for powerlifting and strength training
For lifters, ACWR is most helpful as a trend you glance at, not a dial you obsess over:
- Returning from a layoff or injury? Watch that the ratio climbs gradually instead of spiking back to old volumes in week one.
- Adding a meet peak or a hard block? Expect acute load to rise. The point is to do it on purpose, not by accident.
- Coaches managing a roster can scan everyone's ratios to spot the athlete who quietly doubled their volume.
The smoother companion: EWMA
A block average has a cliff in it: a hard session from 8 days ago counts fully one day and not at all the next. Ægir Iron therefore shows a second read next to the rolling ratio, an exponentially weighted moving average (EWMA) that lets old sessions fade gradually instead of falling out of a window (Williams et al., 2017). When the two reads diverge by more than 0.25, the app flags it and tells you which situation you're in: a one-week spike, a weeks-long climb the 7-day window can't see, or a deload that's registering. The full decoder is in the EWMA guide.
Ægir Iron tracks both reads automatically from your logged sessions alongside per-muscle recovery and relative intensity, so the numbers are a by-product of training normally rather than a spreadsheet chore.
The easiest way to track ACWR
You can compute all of this in a spreadsheet, but keeping the rolling windows accurate week after week is exactly the kind of chore that quietly gets abandoned. Ægir Iron is a strength-training app that calculates your uncoupled ACWR and its EWMA companion automatically from the sets you already log, across powerlifting, weightlifting, strongman, and general strength work, with no spreadsheet to maintain. If you want the number without the bookkeeping, that's what it's built for.
Common questions about ACWR
How do you calculate ACWR? Divide your last 7 days of training load by the average weekly load of the 3 weeks before that. This is the uncoupled method, which keeps the most recent week out of its own baseline. A ratio near 1.0 means this week matched your recent baseline; above 1.0 means you loaded harder than usual.
What is a good ACWR for strength training? Roughly 0.8 to 1.3 is steady, sustainable loading. 1.3 to 1.5 is an elevated, intensification-style week. Above 1.5 is a sharp spike you should only hit on purpose, and below 0.8 is detraining or a deload.
Does ACWR predict injury? No. Later research (Impellizzeri et al., 2020) dismantled the claim that specific ACWR zones predict injury. Treat it as a description of your recent loading and a guardrail against sudden jumps, not a risk score.
What app tracks ACWR for lifting? Ægir Iron computes uncoupled ACWR and an EWMA companion automatically from the sets you log, for powerlifting, weightlifting, strongman, and general strength training, so you get the number without maintaining a spreadsheet.