CTL, ATL and TSB: how to know if you are fresh or carrying fatigue
Training is applying load and recovering from it. If load rises faster than your body absorbs it, performance drops. The three indicators that best summarise that balance are CTL, ATL and TSB.
What each one measures
- CTL (chronic load): exponentially weighted average of your daily load over about 6 weeks. This is your underlying fitness.
- ATL (acute load): exponentially weighted average of the last 7 days. It represents accumulated recent fatigue.
- TSB (balance): simply
CTL − ATL. Positive means you are rested; negative means you are carrying fatigue.
How they are calculated
Daily load can be measured in several ways. The most common option without a power meter is TRIMP, which weights the time spent in each heart rate zone by its intensity. Exponentially weighted averages then give more weight to recent sessions:
CTL = 42-day exponential average · ATL = 7-day exponential average · TSB = CTL − ATL
Reading the TSB
TSB is usually expressed as a percentage of CTL. These bands work reasonably well for amateur runners:
| TSB | State | What to do |
|---|---|---|
| Above +15 | Very fresh / possible detraining | Add quality load again |
| +5 to +15 | Fresh | Good window to race or test |
| −5 to +5 | Neutral | Normal training, demanding sessions |
| −10 to −30 | High load | Training block; watch sleep and how you feel |
| Below −30 | Excessive fatigue | Cut volume, prioritise recovery |
The three usual mistakes
- Chasing the highest possible CTL. A high CTL built too quickly usually ends in injury or a performance dip. The sustained trend matters, not the absolute number.
- Comparing your CTL with someone else's. It depends on the calculation method, the sport and your history. It is only meaningful against your own past.
- Ignoring TSB before a race. Arriving with a clearly negative TSB is the most common way to throw away a personal best you already had in your legs.
How it looks in Afterpacer
The coaching module computes your training load from synced or manually uploaded activities: CTL, ATL and TSB with history, plus a readiness level that summarises whether it is time to push or ease off. Everything relies on the real heart rate of each session, so it is worth reviewing your heart rate zones first.
Training load is available on every plan; the full breakdown and the weekly reports are part of Premium.