Normalized Power (NP)

NP is a weighted average power that reflects the physiological cost of variable efforts better than simple average power. A surgy criterium and a steady tempo ride can have the same average power but very different NPs — the crit's NP will be higher because short hard efforts cost more than easy pedaling saves.

1. Compute rolling 30-second average power at every second.
2. Raise each value to the 4th power.
3. Average those.
4. Take the 4th root. That is NP.

The 30-second rolling window approximates the body's metabolic response time — effort changes faster than 30 seconds are absorbed by anaerobic reserves. Raising to the 4th power captures the non-linear cost of harder efforts.

NP is the 'fatigue-weighted' power. For an evenly paced ride, NP ≈ average power. For a surgy ride, NP may be 10–15% higher than average. The variability index (VI = NP / AP) quantifies how surgy the ride was.