Outsider Lab guide
Acute:chronic workload ratio (ACWR) explained: how to track training load
The acute:chronic workload ratio (ACWR) compares how much you've trained in the last 7 days (acute load) with your average week over the last 28 days (chronic load). Divide the first by the second. Around 0.8 to 1.3 means this week is in line with what your body is used to. Above about 1.5 means you've ramped up much faster than usual, which is a sign to ease off. You can measure load simply as minutes × how hard the session felt, on a 1 to 10 scale.
Step 1: measure each session's load
You need one number per session that captures both how long and how hard it was. The simplest, and one of the most widely used, is session RPE:
The formula
Session load = duration in minutes × RPE
RPE is your rating of perceived exertion for the whole session, from 1 (very easy) to 10 (maximal). A 45-minute steady run at RPE 5 is 225 units; a 60-minute football match at RPE 8 is 480.
The units are arbitrary, but that's fine: you're comparing yourself with yourself. It works across sports, so a gym session, a ride and a match can all go in the same total. Rate the session about half an hour after you finish, thinking about the whole thing rather than the last effort.
| RPE | Feels like |
|---|---|
| 1 to 2 | Very easy: a gentle walk, easy stretching |
| 3 to 4 | Easy: you could chat the whole time |
| 5 to 6 | Moderate: steady, talking in sentences |
| 7 to 8 | Hard: a few words at a time |
| 9 to 10 | Very hard to maximal: race efforts, all-out intervals |
Step 2: work out acute, chronic and the ratio
- Acute load: add up the load of every session in the last 7 days.
- Chronic load: add up the last 28 days and divide by 4, to get your average week.
- ACWR: acute ÷ chronic.
Some coaches use rolling averages that weight recent days more heavily, but the simple version above is easy to follow and is what most people start with.
| ACWR | Zone | What it suggests |
|---|---|---|
| Under 0.8 | Undertraining | Fresher than usual. Room to add volume or a quality session. |
| 0.8 to 1.3 | Sweet spot | Load matches what you're used to. |
| 1.3 to 1.5 | Overreaching | Ramping up fast. Keep the next session easy or short. |
| Over 1.5 | Spike | Much more than usual. Back off for a day or two. |
A worked example
Worked example
Four weeks of training: 1,800, 2,000, 2,100 and 2,500 units, the last being this week.
Chronic: (1,800 + 2,000 + 2,100 + 2,500) ÷ 4 = 2,100 a week. Acute: 2,500.
ACWR: 2,500 ÷ 2,100 = 1.19, in the sweet spot.
Now suppose this week was 3,400 instead, after a tournament weekend. Chronic becomes 2,325, and ACWR is 3,400 ÷ 2,325 = 1.46: overreaching, close to a spike.
The ratio rewards steady increases. Raising your weekly load gradually, rather than jumping, keeps the ratio sensible while your chronic load, your fitness base, builds up behind it.
What ACWR can and can't tell you
ACWR is a useful early warning that you've changed your training quickly. It's not a crystal ball, and sports scientists still debate how well it predicts injury. Use it alongside common sense:
- It needs about four weeks of data before the chronic number means much.
- It ignores what's outside training: poor sleep, illness, stress or a heavy week at work all affect how you cope.
- A low ratio isn't automatically good. After a holiday or illness, return gradually rather than jumping straight back.
- How you feel still counts. Persistent soreness, fatigue or a niggle that gets worse is a reason to ease off whatever the number says.
Tracking load in Outsider Lab
Outsider Lab does the sums as you log.
- Tap ＋ to log a session. Choose a sport (run, ride, swim, strength, HIIT, football and more), the minutes and an RPE from 1 to 10. Heart-rate zone minutes and distance are optional extras.
- See your load. Acute load, chronic load, your ACWR and form (chronic minus acute) update straight away, with a short note on what the zone means. After about two weeks of sessions, the ratio starts to show.
- PRs and squads. Chase personal records, and set up a weekly minutes challenge with friends by sharing a link and result codes, with no accounts.
- Connected apps. If you switch it on, training load can count sessions from Lift Log, Round Timer and Route Run on the same device.
Logging, training load, ACWR and form, PRs, squad challenges, backups and CSV export are free, with no ads and no account. Outsider Lab Pro ($3.99 once) adds a periodised plan generator (Base, Build, Peak and Taper, with a lighter week every fourth week), an interval timer with voice cues and a race predictor.
Common mistakes
- Only logging the hard sessions. Easy runs and walks count towards load too.
- Rating RPE by the last rep rather than the whole session.
- Reading the ratio in week one, before there's a chronic baseline.
- Chasing 1.3 every week. The sweet spot is a range, and easier weeks help you absorb training.
Questions
What is a good acute:chronic workload ratio?
Around 0.8 to 1.3 is usually called the sweet spot. Above 1.5 means you've ramped up much faster than usual, and under 0.8 means you're doing less than you're used to.
How do I calculate training load?
A simple, widely used method is session RPE: multiply the session's minutes by how hard it felt on a 1 to 10 scale. A 40-minute session at RPE 6 is 240 units.
How is chronic load calculated?
In the simple method, add up your load for the last 28 days and divide by 4, to get your average week. Some coaches use weighted rolling averages instead.
Does ACWR predict injuries?
It's a useful warning that training has changed quickly, but research disagrees on how well it predicts injury. Use it alongside how you feel, your sleep and any pain.
Can I use ACWR for any sport?
Yes. Because session RPE uses minutes and effort, runs, rides, gym sessions and matches can all go into the same total.
Is Outsider Lab free?
Yes. Logging, training load, ACWR, PRs, squad challenges, backups and CSV export are free, with no ads. Outsider Lab Pro, a one-time $3.99 upgrade, adds the plan generator, an interval timer and a race predictor.