Free tool

How well do you hold power under fatigue?

Track your performance decay with the Durability Score. A two-step test that compares your fresh 12-minute effort to one performed after a structured fatigue load.

What is the Durability Score?

One number: the percentage of your fresh 12-minute power you can still produce when fatigued. Cadence and heart-rate changes are reported for context, but the score itself comes solely from power: exactly how much of your wattage you keep late in a race, on a long day, or across back-to-back rides.

The thinking behind the score lives in the durability deep dives.

Why it matters

Most training only shows how fit you are when fresh. This shows how you perform when it counts, after you’ve already spent ~1,000 kJ of effort. It reveals your true fatigue resistance, whether you’re training the wrong system, and how much work you can really hold late in the ride.

The 2-step test

How it works

Step 1: Fresh baseline. Perform the structured Day-1 test and record your average power (W), heart rate (bpm), and cadence (rpm).

Step 2: Fatigue protocol + repeat. Perform the Day-2 fatigue protocol, then repeat the same 12-minute effort and record the same metrics. Enter both sets below to get your Durability Score.

The calculator

Run your two tests through the Durability Score.

Go deeper

The full durability system

The calculator measures one number. Why you fade, what is actually breaking, and how to train it is the durability deep dive series.