training load
Training load explained: CTL, ATL, TSB
CTL, ATL, and TSB are the three numbers that summarize whether your training is working. Here is the practical version — no academic asterisks.
You have probably seen the chart with the blue line, the pink line, and the yellow line. That is the training load chart, and the three lines summarize where your fitness, fatigue, and freshness sit on any given day. The math is not complicated. The honesty about what each line means matters more.
CTL — chronic training load
CTL is a 42-day weighted average of your daily training stress. Think of it as fitness — not "how strong you are right now" but "how much work your body has gotten used to absorbing." It moves slowly. A CTL of 70 means you have averaged about 70 TSS per day over the last six weeks.
CTL goes up when you train more than your recent average. It goes down when you do not. Detraining is real, and CTL drops faster than it climbs.
ATL — acute training load
ATL is the same idea over the last 7 days. Think of it as fatigue. A hard week pushes it up. A rest day brings it down. Big single rides spike it.
TSB — training stress balance
TSB is just CTL minus ATL. It is the freshness number.
- TSB strongly negative (-20 or worse). You are deep in a build. Fine for a few days. Not fine for three weeks straight.
- TSB around zero. Steady state. Sustainable.
- TSB positive (+5 to +15). Fresh. Race-ready territory.
- TSB very positive (+20 or more). You have rested too long, or you are detrained.
The practical use
These numbers are not for daily decisions. They are for week-to-week sanity checks.
- If CTL has been flat for a month and you wanted it climbing, you are not doing enough.
- If ATL keeps spiking above CTL+15, you are stacking too many hard days.
- If TSB is below -25, you are about to feel sick or hurt — earn back some freshness.
What they will not tell you
CTL does not know what kind of work you did. 100 TSS of endurance is not the same as 100 TSS of intervals, even though the number is identical. CTL does not know whether you slept. It does not know about life stress. Use it as one input. Listen to your legs as the other.
The line that matters most is the one you draw yourself: am I getting fitter, or am I just getting more tired? CTL and TSB will tell you, if you read them together.