Weighted Average Power (WAP / NP) — What It Is and How to Interpret It
Average power from a ride sounds simple — add up the watts, divide by time. The trouble is that number lies. An interval session averaging 200 W and an easy ride averaging 200 W are completely different loads on your body. Weighted Average Power (WAP) solves that problem.
Why isn't a plain average enough?
Imagine two 60-minute sessions:
- Session A — a steady ride at 200 W for 60 minutes. Average: 200 W.
- Session B — 30 × (1 min at 350 W + 1 min at 50 W). Average: 200 W.
Both rides average 200 W, but session B is drastically harder — the power surges create a higher metabolic load (more lactate, more glycogen used, a longer recovery). Weighted Average Power reflects that.
How is WAP calculated?
The algorithm (developed by Dr. Andrew Coggan):
- Smooth the power data with a 30-second rolling average.
- Raise each smoothed value to the 4th power.
- Calculate the average of those values.
- Take the 4th root of the result.
The 4th power is the key step — it disproportionately "punishes" power surges, because the physiological cost of effort rises non-linearly with intensity.
WAP vs NP — the same thing?
WAP (Weighted Average Power) and NP (Normalized Power®) are, in practice, the same metric. NP is TrainingPeaks' trademarked name, WAP is the generic name for the same calculation. The algorithm is identical.
How to interpret WAP?
| Situation | WAP vs average power | What it tells you |
|---|---|---|
| Steady riding (trainer, TT) | WAP ≈ average (a difference <5%) | An even pace, a low Variability Index |
| A group ride | WAP is 10–20% above average | Variable pace (attacks, climbs, wind) |
| A criterium / race | WAP is 20–40% above average | Very variable load (sprints, attacks) |
Variability Index (VI)
The ratio of WAP to average power:
VI = 1.0 → perfectly steady power. VI = 1.3 → a very variable pace. In time trials (TT) you aim for a VI as close to 1.0 as possible — that means your effort was distributed optimally.
Intensity Factor (IF)
WAP relative to your FTP:
IF tells you how hard the session was relative to your capability. IF = 0.75 is an easy ride. IF = 1.0 is riding at threshold. IF above 1.05 is only possible for short efforts (above-threshold power). More on TSS, which uses IF to calculate total load.
Practical use
- Comparing sessions — WAP lets you compare the load of an interval ride with a steady ride, where a plain average is misleading.
- Pacing in races — keep VI close to 1.0 in time trials; in road races VI will be higher — that's normal.
- Tracking form — the PMC chart uses TSS based on WAP to model fatigue and form.
WAP is the foundation of power-based training analysis. Without it, TSS, power zones and the PMC chart lose their meaning.
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