CTL, ATL, TSB: fitness, fatigue and freshness

If you use Intervals.icu, Garmin or TrainingPeaks, you've already come across these three acronyms: CTL, ATL, TSB. Understood correctly, they help you train at the right time and arrive fresh for your race.

CTL = your fitness (Fitness)

CTL (Chronic Training Load) is an average of your training load over ~6 weeks. It's your baseline fitness: it rises slowly when you train regularly, and drops if you ease off. You build it over time — not in one week.

ATL = your fatigue (Fatigue)

ATL (Acute Training Load) is the same idea but over ~7 days: it reflects your recent fatigue. A big training week makes it climb quickly; a few easy days bring it down.

TSB = your freshness (Form)

TSB (Training Stress Balance) = CTL − ATL. It's your freshness:

• Negative TSB: you're loaded/fatigued (normal during build-up phase, that's where you progress).
• TSB around 0: balance.
• Positive TSB: you're fresh — the state you want on race day for an important event.

How to use it

The principle: build load (negative TSB) to progress, then taper (raise TSB) before an A race. You generally aim for a positive TSB on race day through tapering. See our guide on tapering.

Watch out: these numbers don't replace how you feel. A "correct" TSB but poor sleep, declining HRV or heavy fatigue → ease off anyway. Data guides, your body decides.

The trap of "always in the red"

Staying in very negative TSB for weeks leads to overtraining. You need to alternate loading and recovery (deload weeks) so CTL rises sustainably.

Your coach reads these numbers for you

Sports Coach AI syncs your CTL/ATL/TSB (via Intervals.icu/Garmin), crosses it with your HRV, sleep and how you feel, and adapts each week the load and timing of intensity — to progress without burning out and arrive fresh for competition.