Training load and injury
Training makes you fitter only if your body has time to adapt. Sharp increases in load, such as doubling your mileage after a holiday, are a common cause of overuse injuries. The acute:chronic workload ratio (ACWR) compares what you have done this week with what you are used to.
The calculation
- Acute load: your total load for the last 7 days.
- Chronic load: your average weekly load over the last 4 weeks.
- ACWR = acute load ÷ chronic load
The calculator shows two versions:
- the coupled ratio, where the chronic average includes the current week, as in the original studies;
- the uncoupled ratio, where the current week is compared with the 3 weeks before it, which some researchers prefer.
It also shows the change from last week, since the classic advice is not to increase load by much more than 10% a week.
Interpretation
| ACWR | Meaning |
|---|---|
| under 0.8 | lighter than usual: recovery or taper |
| 0.8 to 1.3 | in line with what you are used to |
| 1.3 to 1.5 | load rising quickly |
| above 1.5 | sharp spike, linked with more injuries in some studies |
Measuring load
Any consistent measure works, as long as you always use the same one:
- session RPE: duration in minutes × perceived exertion from 0 to 10, a method developed by Carl Foster;
- distance for runners, swimmers and rowers;
- training stress score from a power meter for cyclists;
- total sets × reps × weight for strength training.
Example
With weekly loads of 1,700, 1,800 and 1,900 units over the past three weeks and 2,400 this week, the chronic load is 1,950 and the coupled ACWR is 1.23, within the sweet spot. But the jump from last week is 26%, and the uncoupled ratio is 1.33: a sign to keep an eye on fatigue.
Limits
The ACWR, popularized by Tim Gabbett around 2016, has been debated. Critics point out that the coupled version is mathematically biased and that the evidence for predicting injuries is inconsistent. Injury risk also depends on sleep, stress, nutrition, previous injuries and technique. Use the ratio as one signal among others, and progress gradually.