What is TSS and how is it calculated?
TSS measures the load of each workout by combining duration and intensity. What it means, how it is calculated and what it is for.
TSS (Training Stress Score) sums up in a single number how much a workout has loaded you. It combines two things: how long you trained and how hard, relative to your threshold.
The reference: one hour flat out
By definition, one hour exactly at threshold is worth 100 TSS. An easy hour may stay at 40 or 50; a hard interval session can reach 90 or more even if it's shorter.
How it's calculated
The formula multiplies duration by the square of relative intensity. That's why intensity weighs so much: going a little faster raises load far more than going a little longer.
- With power, normalized power is compared with FTP.
- When running, pace is compared with threshold pace (rTSS).
- Without power or reliable pace, heart rate is compared with threshold heart rate (hrTSS).
What it's for
A single TSS says little. Its value lies in adding it up day by day: that gives you fitness, fatigue and form, which tell you whether you're building or just piling up tiredness.
Traincontrol calculates the load of every session with the best reference available: power, pace or heart rate, and in the mountains it takes elevation into account.