Durability is how well your power holds up deep into a long ride. Your FTP tells you what you can hold for about an hour. Durability estimates what's left at three, five and seven hours.
What the number means
The score runs from 0 to 100. It comes from your predicted power after 5 hours, as a share of your FTP:
| 5-hour power | Score |
|---|---|
| 60% of FTP or less | 0 |
| 85% of FTP or more | 100 |
The score rises in a straight line between those two points. The labels are:
- Developing: below 35
- Moderate: from 35
- Strong: from 55
- Elite: from 80
The card also shows your predicted watts at 3, 5 and 7 hours.
What it's built from
The prediction starts from your power curve and adds a fade that grows with time, plus extra fade for glycogen running low after about three hours. The card lists what set your fade rate:
- Cardiac decoupling from your steady endurance rides. Less heart-rate drift means a slower fade.
- Long ride history: how much your power actually dropped from the first half to the second half of your rides of two hours or more. It needs at least three of them.
- Efficiency trend: a clearly improving efficiency factor at endurance pace slows the fade a little.
- Baseline estimate: used when none of the above is available yet.
Confidence
- High: the score uses both your decoupling and your long rides.
- Medium: it uses one of them.
- Low: it uses neither, so it's mostly the baseline. Ride a few steady long rides with power and heart rate, and the number becomes yours.
Raising it
Ride long and steady, and fuel well. Regular rides of three hours or more at endurance pace, with carbohydrate on board, build exactly what this score measures.
For the full explanation, read What Is Durability in Cycling and How WattPlan Scores It.