What TSS and IF measure
Training Stress Score (TSS) and Intensity Factor (IF) are training load metrics devised by exercise physiologist Andrew Coggan for cyclists who train with a power meter. TSS, IF and Normalized Power are trademarks of Peaksware, the company behind TrainingPeaks; this calculator applies the published formulas.
- Intensity Factor: IF = Normalized Power ÷ FTP. It says how hard a ride was compared with your functional threshold power, the power you can hold for about an hour.
- Training Stress Score: TSS = (seconds × NP × IF) ÷ (FTP × 3,600) × 100, which simplifies to hours × IF² × 100.
One hour ridden flat out at FTP therefore scores 100 TSS by definition.
Normalized or average power?
Normalized Power weights hard efforts more than easy ones, because the body’s cost rises faster than power. It is computed from a 30-second rolling average raised to the fourth power. On a steady ride, average power is close to Normalized Power. On a ride with sprints, climbs and freewheeling, average power is lower and gives a TSS that is too low, so use the Normalized Power from your bike computer when you have it.
How to read the results
| TSS of one ride | Typical recovery |
|---|---|
| under 150 | usually recovered by the next day |
| 150 to 300 | some fatigue the next day, gone by the second |
| 300 to 450 | fatigue often still there after two days |
| over 450 | fatigue can last several days |
| IF | Type of effort |
|---|---|
| under 0.75 | recovery or easy endurance |
| 0.75 to 0.85 | tempo, solid endurance |
| 0.85 to 0.95 | threshold intervals, road races |
| 0.95 to 1.05 | time trial of about one hour |
| over 1.05 | short efforts under an hour |
Example
A two-hour ride with a Normalized Power of 200 W for a rider with an FTP of 250 W has an IF of 0.80 and a TSS of 2 × 0.8² × 100 = 128.
Using TSS over weeks
Daily TSS feeds three common curves: chronic training load (a 42-day weighted average, a proxy for fitness), acute training load (7 days, a proxy for fatigue) and their difference, training stress balance, often called form. Raise weekly load gradually and recheck your FTP every 6 to 8 weeks, because an outdated FTP distorts every score.