What is Training Stress Score?
One number for a workout
Training Stress Score (TSS) combines a workout’s duration and intensity relative to your threshold. In the cycling power version, one hour at an intensity factor of 1.0 gives 100 TSS. It is a way to summarise a session, not a direct measurement of how tired you are.
Change the duration and intensity below. Two hours at an intensity factor of 0.70 gives 98 TSS; one hour at 1.00 gives 100. Their scores are close, but the sessions are not interchangeable.
Build a workout
Set the duration and power of a cycling workout.
Cycling power example: TSS = hours × (Normalized Power ÷ FTP)² × 100. The selected values are assumptions, not a workout prediction.
One number for a workout
Training Stress Score (TSS) combines a workout’s duration and intensity relative to your threshold. In the cycling power version, one hour at an intensity factor of 1.0 gives 100 TSS. It is a way to summarise a session, not a direct measurement of how tired you are.
Change the duration and intensity below. Two hours at an intensity factor of 0.70 gives 98 TSS; one hour at 1.00 gives 100. Their scores are close, but the sessions are not interchangeable.
How the calculation works
Intensity factor is Normalized Power divided by FTP. For power-based cycling TSS, multiply duration in hours by intensity factor squared, then by 100. The square means intensity changes the score disproportionately: one hour at 0.80 gives 64, not 80.
Normalized Power is a modelled summary of a variable power trace. FTP is an estimate or setting, so the final score depends on both the quality of the recording and the threshold used.
A score is not the whole workout
Two sessions with similar scores can differ in intervals, muscle demands, technique and recovery. A long easy ride and a short hard session are not equivalent just because their totals are close.
Heat, sleep, illness, life stress and how you felt are not measured by the power-based formula. Use the score alongside the session and your own response.
Check before comparing
Keep threshold settings current and compare the same scoring method. Different platforms may estimate load from heart rate, pace or perceived effort when power is unavailable; these are different inputs and may not match power-based TSS.
A missing workout or sensor gap changes the picture. Check whether activities are included and whether a score is measured or estimated before interpreting a trend.
A week is more than its total
Suppose one week contains five similar easy sessions and another contains two demanding sessions plus rest. Even if both sum to the same TSS, their pattern and the demands of each session differ.
Use a weekly total to notice changes in the amount of recorded training, then open the calendar to see how that load was distributed.
Why a threshold change matters
A ride recorded at the same power gets a different score when the FTP used in its calculation changes. For example, an hour at 200 W Normalized Power scores 64 at an FTP of 250 W, but about 44 at 300 W.
Platforms differ in whether they preserve the threshold used at the time or recalculate older activities. Check the platform’s behaviour before interpreting a sudden step in history.
When you do not have power
Heart-rate, pace and perceived-effort approaches can give useful context, but each responds to different things. Heart rate can drift; running pace changes with terrain; perceived effort is subjective.
Keep the method visible and compare like with like. Do not assume a score estimated from another signal reproduces cycling power-based TSS.