Power reading outside versus inside

I completed a 90 minute workout under build phase sustained power build. It was a hard workout and it took everything I had to complete the workout. My numbers said I had a NP of 205. Last weekend I did a 4+ hour ride outside and had a similar NP of 205. How can I do a 4 hour ride and have a similar NP as a 90 minute indoor ride that was very hard? I seem to be able to generate more power outsider versus on the trainer. Does anyone know why? Thanks.

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Steady state rides without a lot of spiky power (long intervals like on a trainer) have NP and Avg Power being very close. Rides with many spikes in power (quick accelerations, jumps up hills, etc; typical of outside rides/races) can have NP being much higher than Avg Power.

My guess is your raw average outside was a bit lower than your 90 minute inside ride raw average power.

The regular questions: Same bike? Same power meter?

Assuming the same other factors can be cooling (eg. less inside) and type of workout. For example indoors holding power for long periods of time vs outdoors where power could be more spikey may generate similar NP’s but different stressors.

I suspect someone will be able to post a link to a thread that goes into a lot of detail on this.

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Happens to me every single outdoor ride, and an overrated NP means overrated IF and TSS.

My points:

  • Indoors FTP (lower) used to ride outdoors.
  • Lot of time spent at VO2max and Anaerobic power zones
  • Spiky power riding.
  • High short power capabilities compared to FTP.