Question 1

What is a power-duration curve?

Accepted Answer

It is the relationship between how hard you can ride and how long you can hold it. Plotting your best power at each duration traces a curve that falls steeply over the first few minutes and then flattens toward a sustainable asymptote. Modelling that curve lets you estimate efforts you have not directly tested.

Question 2

What are Critical Power and W′?

Accepted Answer

Critical Power (CP) is the asymptote of the curve — the highest power you can sustain in a metabolic steady state. W′ (pronounced "W prime") is the fixed amount of work you can do above CP before exhaustion, drawn from anaerobic reserves. The CP and W′ concept comes from Monod and Scherrer (1965) and was extended by Jones and colleagues.

Question 3

How many efforts do I need to enter?

Accepted Answer

At least two. A short effort (5 seconds to 1 minute) anchors peak power, while a 5-minute and a 20-minute effort anchor Critical Power and modeled FTP. The more durations you provide, the better the fit — the calculator flags gaps that make the model extrapolate.

Question 4

How is modeled FTP derived?

Accepted Answer

Modeled FTP is estimated as 95% of your best 20-minute power, following Allen and Coggan. It is shown alongside Critical Power because the two answer slightly different questions: FTP is a practical 20-minute-based anchor, while CP is the mathematical asymptote of the curve.

Question 5

Does this calculator require a Gradescale account?

Accepted Answer

No. The power-duration curve calculator is free to use without an account. Connecting your account fits the curve automatically from your ride history instead of manual entry.

Power-Duration Curve

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