Freshness (TSB): fitness minus fatigue
Updated October 3, 2026 · Source: Banister impulse-response model · CTL/ATL/TSB vocabulary from Coggan
01What it is
The gap between your fitness and your fatigue: do you feel fresh or worn down? Fitness (CTL) is your training level over about 6 weeks, fatigue (ATL) is the load of the last 7 days.
02How it’s calculated
TSB = CTL − ATL (from the day before) CTL (fitness): exponential moving average of the daily loads (TRIMP), with a 42-day constant.
ATL (fatigue): same calculation with a 7-day constant.
03How to read it
| TSB | Reading | What it means |
|---|---|---|
| > 0 | Fresh | You are fitter than tired. |
| 0 to −20 | Normal training zone | Usual training. |
| −20 to −30 | Marked fatigue | Plan to ease off. |
| < −30 | Rest advised | Runalis replaces the next run with rest. |
04What it’s used for
Freshness feeds your morning readiness, and triggers a rest day when it drops below −30.
05Limits
A normal training week already makes it swing between −12 and +4: a slightly negative value is not a problem. It does not account for sleep or stress.
Runalis is not medical advice. If you feel pain, stop and see a health professional.
