Normalized Power

Normalized Power (NP) is the constant power output that would have produced the same physiological load as the actual, fluctuating power of a ride.

Definition

“Normalized Power” (NP) is the constant power output in watts that would have caused the same physiological load as the actual, variable power of a ride. The term was coined by Andrew Coggan and popularised by TrainingPeaks.

Unlike average power, NP weights high power spikes disproportionately, because fatigue does not rise linearly with power. For running, Normalized Graded Pace plays the same role on the basis of pace.

Why it matters

Two one-hour rides averaging 200 W each can differ greatly in their load. On an indoor trainer power stays almost constant; in hilly terrain, spikes of 300–400 W alternate with coasting phases at zero.

Average power claims both rides were equally hard. Subjectively and metabolically the second is far more demanding, because every spike burns anaerobic energy that is only partly replenished while coasting. NP makes this difference visible, which is why it is the basis for Intensity Factor and Training Stress Score.

How obseed measures it

obseed computes NP from the power meter’s one-second data following Coggan’s method:

1. Rolling 30-second average of power
2. Raise each average to the fourth power
3. Take the mean of those values
4. Take the fourth root

As a formula: NP = (mean(P30s^4))^(1/4). The fourth power ensures that short, high spikes carry heavy weight. The ratio VI = NP / average power (Variability Index) also shows how uneven the ride was; values above 1.10 indicate a very irregular session.

To place NP in zones, obseed uses the thresholds from spiroergometry. An NP of 250 W only becomes meaningful once it is known whether the second ventilatory threshold sits at 240 or 270 W, and an FTP field test answers that question with considerable uncertainty.

Example

A simplified calculation with four 30-second segments instead of a full hour:

Segment	Power (W)	Power^4
1	150	506,250,000
2	350	15,006,250,000
3	100	100,000,000
4	200	1,600,000,000

Average power: (150 + 350 + 100 + 200) / 4 = 200 W.

Mean of the fourth powers: 17,212,500,000 / 4 = 4,303,125,000. Fourth root: NP ≈ 256 W.

NP sits 56 W above the average and the Variability Index is 256 / 200 = 1.28. On the trainer at a constant 200 W, NP would be exactly 200 W and VI 1.00. With a VT2 of 260 W, the hilly ride was a threshold session and the steady ride a base session.

References

Allen, H. & Coggan, A.: “Training and Racing with a Power Meter”.