Acute to chronic workload ratio: how much training load is too much?

Every injury-prevention article eventually produces a number: keep your acute-to-chronic ratio under 1.5. The number is real, the research behind it is more contested than the number suggests, and the useful version of the advice is simpler than either.

What is the acute to chronic workload ratio?

Acute load is roughly this week's training. Chronic load is your rolling average over the previous four weeks or so. The ratio is one divided by the other, and it asks a single question: is what you are doing now a lot, compared to what you are used to?

Gabbett's work popularised it, along with the finding that risk rises steeply above a ratio of roughly 1.5 in the original cohorts, and the accompanying and more interesting claim: high chronic load is protective. Athletes who had built up to a lot of training were more robust than those who had not. The danger is not volume. It is the spike relative to your own history.

That reframing is the part worth keeping. "Am I doing too much?" has no absolute answer. "Am I doing much more than I have recently been doing?" has one.

How do you calculate it?

By hand, the simple version takes four weeks of training totals.

1. Give every session a load. The crudest version is minutes; a better one is minutes multiplied by an effort score from 1 to 10.
2. Add up this week: that is acute load.
3. Average the last four weeks, including this one: that is chronic load.
4. Divide acute by chronic.

The bands are a direction of travel, not a safety line, for reasons the next section covers.

PeakU does this from your own data. A coach that reads everything you already track. Join the free beta →

Where is the 1.5 number weaker than it sounds?

The methodology has taken sustained criticism since: the way the ratio is computed, how loads are coupled between numerator and denominator, and how thresholds were derived have all been challenged, and some of the original sport-specific findings have not replicated cleanly elsewhere.

What survives the criticism is the underlying direction rather than the exact cut-off. Rapid increases in load relative to your recent norm are associated with more injuries; gradually built high loads are not the same risk. Treating 1.49 as safe and 1.51 as dangerous was never supported by anything. Treating a sharp jump as worth noticing always was.

Does the 10 percent rule work?

As a specific rule, it is weakly evidenced; the systematic review by Damsted and colleagues found the evidence linking changes in running load to injury inconsistent in detail. As a principle, that your connective tissue adapts more slowly than your cardiovascular system and so volume should climb gradually, it holds up well. The 10% figure is a convenient way to say "gradually" with a number attached, not a threshold anyone has measured.

The corollary matters more: weeks after time off should start lower than where you stopped. Fitness returns faster than tendon tolerance, which is why the comeback week after a holiday is one of the most common injury weeks there is.

The version you can actually use

Ramp gradually. Roughly 10% a week, with the long run growing by no more than 2 km at a time, is how the 12-week half marathon plan is built.

Build a down week in. Every third or fourth week at roughly half volume. This keeps chronic load high without letting acute load stay high, which is the combination you want.

Count everything. The most common way to blow up a ratio is not to count the lifting, or the cycling commute, or the walking. An incomplete load count produces a comfortable ratio and an uncomfortable Achilles. Loaded walking counts too; a weighted pack turns a walk into a session, as the rucking evidence makes clear.

Weight intensity, not just duration. Ninety easy minutes and forty hard ones are not the same load. Anything that multiplies duration by an intensity factor beats counting hours.

Watch the direction, not the decimal. A ratio drifting up across three weeks matters. Today's value to two decimal places does not.

Because the ratio is only as good as the count. A lifting app sees two heavy sessions and calls it a normal week; a run app sees a tempo and a long run and calls it a normal week; added together they are a spike no single app can see. This is the core of why fragmented fitness apps stall progress, and it is why the ratio, for all its flaws, is almost never computed for the people who would benefit from it most.

What does too much training load feel like?

Usually it does not feel like anything until it does. That is the problem the ratio exists to solve: tendons and bone do not send a warning at 1.4, they send one at the point of injury.

The early signs that do show up are the ones in the overreaching literature: easy pace costing more heart rate than it should, sleep worsening as training climbs, a resting heart rate drifting up for two or three weeks. How to know if you are overtraining lists the cluster and the down-week test that settles it.

If the ratio is high and none of those signs is present, you are probably fine to hold, not to climb. If the ratio is high and two of them are present, the down week is overdue.

How long does chronic load take to build?

About as long as the window you average over, which is the point of the four-week average: it takes a month of consistent training for the denominator to catch up with a new level of volume. That is why a step up in training feels risky for three or four weeks and then stops feeling risky, and why the first month after a holiday is the one to take carefully. The protection Gabbett described comes from chronic load that is genuinely chronic: built over months, not announced in a week.

It also means that a single big week does less damage than it feels like it should, provided the next week comes back down. One spike is a bump in the ratio; three in a row is a ramp the denominator cannot absorb.

What PeakU does with this

Computing this by hand fails at the first step, which is the complete count. PeakU takes workouts from Apple Health or Health Connect, strength sessions from Hevy and runs from Strava, puts them on one intensity-weighted scale, and computes acute and chronic load across the lot.

The ratio is shown with its drivers rather than as a bare number, so you can see whether it moved because of the long run or because of two heavy lower-body days. Running plans are audited against ramp rate and hard-day spacing before you ever see them, and when readiness drops the plan reflows rather than holding a ramp your body has stopped agreeing to.

Hen Eytan · Founder, UPeak

Builds the UPeak apps and writes up the research behind them.