CTL, ATL and TSB explained simply
Fitness, fatigue and form: what CTL, ATL and TSB are, how they come from TSS and how to read them without overthinking.
They're the three most widely used curves for tracking training load. They sound like jargon, but they answer three very simple questions.
CTL: your fitness
The average load of roughly the last six weeks. It rises slowly when you train consistently and falls slowly when you stop. It's your underlying fitness.
ATL: your fatigue
The average load of the last week. It reacts quickly: it rises after a few hard days and drops as soon as you rest.
TSB: your form
The difference between the two. If fatigue exceeds fitness, TSB is negative: you're loaded. If it's positive, you're fresh.
- Very negative (below -30): lots of fatigue; be careful.
- Between -10 and -30: a productive training block.
- Around zero: balanced.
- Positive: rested; what you want before a race.
How to use them
Look at trends, not single days. Fitness rising week after week with form under control is the sign the plan is working. Traincontrol shows you all three curves and also translates them into words: fresh, balanced or loaded.