Originally Posted by
PeteHski
Strava doesn’t measure “Normalized Power” like Garmin. They have their own proprietary “Weighted Average Power” which for me always gives a lower value. There is no right or wrong here, they are both proprietary attempts to normalise average power to take account of how lumpy your terrain was.
I'm not sure how proprietary either is. Garmin NP seems to agree with NP as originally described by Coggan, and Strava "weighted power" seems to agree with Skiba's xP. Part of the issue is that TrainingPeaks claimed a trademark on the name "Normalized power" (which surprised me, since they didn't come up with that name -- um, I did) and wanted a licensing fee to use it.
Neither NP nor "weighted power" should be used for calorie (or Calorie) calculations.