Training Stress Score (TSS)
TSS (Training Stress Score) sums up the total load of a session in a single number, based on duration and intensity relative to your threshold. That makes sessions and training weeks comparable — the foundation under terms like fitness (CTL) and form (TSB).
In Trimetra this is called session load.
What is TSS?
The scale’s reference point is simple: one hour all-out at your threshold works out to about 100 points. An easy hour of endurance scores well below that; a long day on the bike can go far above it.
Intensity counts more than proportionally in the model: an hour at a hard pace loads you considerably more than two easy half-hours. So the score doesn’t simply reward "lots of hours", but the combination of duration and how deep you went.
How is TSS calculated?
The score is derived from your output relative to your sport-specific threshold anchor: power versus FTP in cycling, pace versus threshold pace in running, swim pace versus CSS in swimming. If that data is missing, heart rate relative to your LTHR is a common fallback.
The key thing to remember: TSS is a calculation model, not a physiological measurement. The score is only as good as the threshold anchor underneath it — if your FTP or threshold pace is set out of date, every load score that leans on it is systematically too high or too low. And two sessions with the same TSS can feel very different; sleep, stress and how you feel stay separate signals.
How Trimetra personalises this
Trimetra calculates the load of every session sport-specifically on your own anchors (FTP, threshold pace, CSS, LTHR) and uses those scores in your load build-up and daily planning. Because the quality of the score stands or falls with your anchors, the app actively watches them and suggests adjustments as soon as your data gives reason to.
Frequently asked questions
What does 100 TSS mean?
That’s the calibration point of the scale: one hour flat out at your threshold equals roughly 100 points. An easy one-hour endurance session scores well below that; a long day on the bike can go far above it.
How much TSS per week is normal?
There is no universal norm: what fits depends on the base your body is used to. The same week is routine for one athlete and a sharp spike for another. Your build-up relative to your own history says more than the absolute number.
Why doesn’t your TSS match how hard it felt?
TSS is a calculation model, not a measurement: the score is only as good as the threshold anchor underneath it, and an outdated FTP or threshold pace makes every score too high or too low. The model also doesn’t see sleep, stress or daily form — two sessions with equal TSS can land very differently.
Every term at a glance in the full glossary.
TSS, NP, IF, CTL, ATL and TSB are trademarks of Peaksware, LLC (TrainingPeaks). Trimetra is not affiliated with them; this page merely explains the term.