ACWR explained: acute and chronic workload for climbers

Most training injuries are not caused by one bad move. They tend to show up when what you are asking of your body suddenly outpaces what it is prepared for. The acute:chronic workload ratio, usually shortened to ACWR, is one attempt to put a number on that mismatch.

Two kinds of load

• Acute load is what you have done recently. In Train Climb, that is your total load over the last 7 days.
• Chronic load is what you are used to. In Train Climb, that is your average weekly load over the last 4 weeks.

The ratio divides one by the other. If this week's load matches your recent average, the ratio is close to 1.0. If this week is double your average, it is close to 2.0. If you are taking it easy, it drops below 1.

You can think of chronic load as your fitness for training: the work your tissues have been gradually adapting to. Acute load is the fatigue you are currently carrying. A sensible plan grows chronic load steadily without letting acute load race too far ahead.

Where the idea comes from

The ratio became popular through work by Hulin, Gabbett and colleagues in team sports such as cricket and rugby. Gabbett (2016) summarised much of this in a widely read paper on the "training-injury prevention paradox". His central message was that hard training is not the enemy. Athletes who had built up high chronic loads were often more robust, while sharp spikes in load relative to what athletes were used to were associated with more injuries.

That message resonates with climbing. Fingers, pulleys and tendons adapt more slowly than muscles, and a sudden jump in hard crimping, for example on a trip or right after a break, is a familiar story behind finger injuries.

Train hard, but build up to it. The ratio is a reminder to respect what your body is used to.

How to read the zones

Train Climb shows the ratio with three zones:

These zones are deliberately broad. They are prompts for attention, not verdicts. A Watch week before a planned trip might be perfectly reasonable. A High week after illness deserves a careful look.

Why the ratio needs history

The ratio is meaningless without a chronic baseline. If you only started logging last week, there is nothing to compare against. That is why Train Climb only shows the ratio once there are 2 earlier weeks of training. Before then, focus on logging consistently.

Gaps in logging also distort the picture. A week you trained but did not log makes your chronic load look smaller, which makes the next logged week look like a spike.

Practical guidance for climbers

1. Build gradually after breaks. Returning from holiday, illness or injury is when the ratio is most likely to jump.
2. Watch trips and comp weekends. A long outdoor weekend can easily double a normal week. Plan easier days around it.
3. Do not chase a perfect 1.0. Training needs some variation. Deload weeks will push the ratio down, and the following build week will push it up.
4. Combine the number with how you feel. Sore fingers in an OK week still matter.

The ratio has real limitations, and researchers have debated it vigorously. Read What the acute:chronic ratio can and can't tell you for the balanced view.

In Train Climb

• Open Progress to see your weekly load and the acute:chronic ratio with its OK, Watch and High zones.
• Log every session, including easy ones, so your chronic load is accurate.
• Coaches can see athletes drifting into Watch or High on the team board and adjust upcoming weeks in the planner.
• The ratio also feeds into the injury-risk light, alongside morning check-ins and skipped sessions.