Training load explained: ATL, CTL and TSB without the jargon
Three abbreviations, one concept: how ATL, CTL and TSB connect and why your TSB shouldn't always be positive.
ATL, CTL, TSB. Three abbreviations that show up in every serious training analysis, and three numbers that amateur athletes routinely struggle with. The concept behind them isn't actually that complicated once you translate it into plain language.
The three values in one sentence
- CTL (Chronic Training Load) = your fitness. How much load your body has gotten used to over the past weeks. Rises slowly, falls slowly.
- ATL (Acute Training Load) = your fatigue. How much load has come in over the past few days. Rises and falls fast.
- TSB (Training Stress Balance) = your form. The difference between CTL and ATL. Positive = rested, negative = drained.
How is it calculated?
Both values are exponentially weighted averages of your daily training load (TSS, Training Stress Score). CTL weights the last 42 days, ATL the last 7 days. A hard session yesterday weighs heavily on ATL, barely on CTL. A hard session three weeks ago no longer shows up in ATL, but still shapes your CTL.
TSB is simply CTL − ATL. If your CTL is 70 and your ATL is 85, your TSB is −15. You're under load right now.
How to read your TSB
Rough ranges, no hard limits, but a useful guide:
- +15 to +25: taper-fresh. Ideal for a race or a performance test. If you feel like this all the time, you're undertraining.
- +5 to +15: rested, capable. Good zone for hard key sessions.
- −5 to +5: neutral. Training rhythm is dialled in.
- −10 to −25: classic training phase. You're building form, but you're not fresh.
- Below −30: careful. Risk of overtraining, illness, performance drop. Planned overload phases can sit there briefly, but not for long.
The typical training cycle in TSB
A well-planned block looks like this: three weeks of load (TSB drops from 0 to −20), one recovery week (TSB climbs back to 0 or slightly positive). Before a season peak: two weeks of taper, with TSB rising from −15 to +15. That transition is exactly when supercompensation happens.
Common misconceptions
„I have to keep my TSB positive at all times." Wrong. Anyone who never dips below −10 isn't building form. Load has to happen, otherwise CTL stagnates.
„CTL = fitness, so higher is better." Only half right. CTL is training volume, not performance directly. Riding 1000 km per week unstructured produces high CTL and still no top form. Quality beats quantity.
„My TSS from the run doesn't count for my bike CTL." It does, depending on the view. trace tracks run and bike load separately, but also shows you a combined training load where both sports are merged.
How to actually use the numbers
Plan your key sessions in TSB ranges above 0. Plan your volume weeks in TSB ranges below −10. Pay attention to the TSB level at which you personally start to feel overloaded. That's very individual. Some happily ride at −25, others absolutely need a recovery day at −15.
The numbers are a tool, not the training journal itself. They don't replace your feel for your own body, but they keep that feeling from steering you in the wrong direction.