Research points to a “sweet spot” between roughly 0.8 and 1.3. Within that range injury risk is lowest. It is a guideline, not a guarantee — always listen to your body too.

Which load do I enter: kilometers or minutes?

Either works, as long as you are consistent. Kilometers are simplest. To factor in intensity, use training minutes × perceived exertion (sRPE) for both the acute and chronic values.

Why is a sudden spike risky?

Your tissue adapts to the load it is used to. A sharp spike gives it no time to get stronger, raising the risk of overuse injuries — even when the absolute volume is still modest.

How do I use this alongside a plan?

Use the ACWR as a safety check on top of your plan. Our personal plan already builds your volume up in a controlled way, but this tool helps you judge whether an extra week or a catch-up is wise.

Training load calculator — acute:chronic workload ratio (ACWR)

Acute

This week

Chronic

Last 4 weeks

km per week

Load

Assessment

ACWR

1.13

Safe zone

This week: 45 km
Average per week: 40 km

Assessment	ACWR
Undertraining	0.0 – 0.8
Safe zone	0.8 – 1.3
Caution	1.3 – 1.5
Elevated risk	> 1.5

How it works

How does the acute:chronic ratio work?

The ACWR divides this week's load (acute) by your average weekly load over the last four weeks (chronic). A ratio of 1.0 means this week matches your habit. If the ratio jumps well above that, you are stacking load faster than your body can absorb.

Good to know

The zones explained

Below 0.8 you are tapering or training lightly. Between 0.8 and 1.3 is the “sweet spot” with the lowest injury risk. Between 1.3 and 1.5 calls for caution. Above 1.5 the risk of overload rises sharply — a large, sudden spike is more dangerous than a high absolute volume.

Tips

Building up sensibly

Increase your weekly volume gradually (the well-known 10% rule is a rough guide). Schedule recovery weeks and take extra care after illness or injury, when your chronic base has dropped and a normal week suddenly produces a high ratio.

FAQ