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AnswersWhat is Training Stress Score?
Training Stress Score, or TSS, is a single number for how hard a session was, combining how long it lasted with how intense it was. It is calculated as hours × intensity factor² × 100, so an hour at threshold is 100. Because it works the same way for running, riding and swimming, it is how a multi-sport plan can add the sports together and manage one total load.
Load for one hour at each intensity
| Intensity | TSS for 60 minutes |
|---|---|
| Zone 1 · intensity factor 0.55 | 30 |
| Zone 2 · intensity factor 0.7 | 49 |
| Zone 3 · intensity factor 0.84 | 71 |
| Zone 4 · intensity factor 0.97 | 94 |
| Zone 5 · intensity factor 1.06 | 112 |
Why the square matters
Intensity is squared, so it dominates. Two hours easy scores less than one hour at threshold. That matches how training feels: a long easy ride leaves you tired but recovered by tomorrow, while an hour of hard intervals can take days. A load number that simply added up minutes would badly under-count the hard days.
For a triathlete, TSS is what stops the plan from quietly overloading. A run plan that looks sensible and a bike plan that looks sensible can add up to a jump that neither shows on its own. Race Shape applies its weekly ramp ceiling to the combined number.
A week of load, added up
| Session | TSS |
|---|---|
| Monday — 60 min easy ride | 49 |
| Tuesday — 50 min run, 20 min of it at threshold | 55 |
| Wednesday — 45 min technique swim | 23 |
| Friday — 75 min ride, 45 min at sweet spot | 77 |
| Sunday — 90 min easy run | 73 |
| The week | 277 |
No single session in that week is large, but together they are a real training load — and next week's total is what the plan compares it with, not any one session.
Common questions
What is a normal weekly TSS?
It varies enormously with experience and time available. What matters is how it changes week to week.
Is TSS the same across sports?
Calculated the same way, but a TSS point of running costs more recovery than one of swimming, because running has more impact.
Who created TSS?
Andrew Coggan, originally for cycling power data.
Sources
- Allen, H. & Coggan, A. Training and Racing with a Power Meter.