NP vs average power outside

This might be a dumb question, but when I occasionally do my workouts outside, my NP is always quite a bit lower than my average power. When I do my intervals indoors on my “dumb” trainer, they’re almost identical, or NP is slightly higher.

Why is NP lower outside if I’m moving my legs the entire time?

I don’t necessarily have a great answer, but one thing that can greatly skew riding outside is the “Include or Exclude Zeros for Power” option.

  • For proper power data, you need to INCLUDE Zeros for proper power data accuracy. So that is one thing to check right away.
  • This implies that you never coast outside. Is this really true? Can you share links to files for review?
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I’ll definitely check on including zeros.

I should have clarified that I mean my legs are moving during the intervals, I’m definitely coasting during rest intervals when outside. Also dumb question, but how does one share their ride files? Data analysis dummy here when it comes to my cycling.

For sharing TR rides, you can open your rides on the TR website, copy that browser link and post here. Note, this method requires you to have a “Public” setting for your account vs “Private”.

As to your NP vs AP, are you talking about single intervals, or entire workouts?

  • If you are talking about shorter intervals, that is likely a misuse of NP. It is noted as likely to be misleading for shorter intervals (anything less than 20 minutes IIRC, but that could be wrong), so take care to avoid placing too great of importance to those short data times.

Edit to add a related discussion:

Did u possibly transpose avg and NP? NP should be higher except when there is no variation in power, then NP = Avg power


Yes, that struck me as odd too. I only recall one or two trainer rides (in my pre-TR days) where my NP is lower than the average power. I’ve seen a few rides where they are identical and the vast majority of rides NP > AP even if only by a few watts.

On the ride or two where NP < AP, my recollection is I was trying to keep HR even and I would reduce power to bring my HR down back to my target and then when I was back in HR spec I would bring my power back up…

NP is calculated as:

Take the rolling 30sec average power 0-30,1-31sec,2-32sec etc

Raise each to the fourth power

Take the average of the results

Take the fourth root of that average

It can never be less than a simple average except perhaps if the effort consists of intervals so short that NP can’t really be calculated

Here’s a link to several outdoor workouts I completed this fall. This trend is consistent every time I go outdoors though.

I’m talking about individual intervals. The issue gets worse the shorter the interval but is always still present when I’m outdoor. I realize it’s an overemphasis, I’m just curious why this is happening as I don’t see this indoors at all.

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In the linked article they mention autopause being an issue. I’ve been using a wahoo element bolt with autopause since I started using TR so I do wonder if that’s part of the issue. I’ll have to try my next workout with that turned off and see if there’s a difference.

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Ok. I see now what you are saying

I think the lap function of the wahoo is not restarting the NP calculation. It is just a time stamp. NP is calculated beginning at the 30th second. I suspect that the Wahoo is using power from before the interval started to have a running avg from the first second of the interval for the NP calculation

Try looking at NP for the first 30 seconds of an interval outdoors. It shouldn’t progressively climb from the pre-interval power to the interval power over those 30 seconds. NP should be blank until second 30

Oh wow, good catch! You’re 100% right! If you zoom in on say the last 2 minute of the 3 minute intervals NP is close to, if not slightly higher, than the average power like you’d expect.

Thanks for the help! I had been a little confused as to whether I should be looking at average power or NP for my interval compliance when I’m outside and mistakenly thought NP was the better metric so this issue was super confusing.

Hmmm, maybe I did something something wrong but I ginned up some numbers and applied that calculation and I came up with an NP calculation lower than the average. NOW I want to scale those numbers up and perform the workout to see if it holds. Also, worth noting is the difference was NOT huge.

Still, I distinctly remember 1 trainer session where the NP was less than the average. However, trying to find it is not an easy thing – none of my tools allow me to write custom queries for this. I did stumble on one ride where that held but it was about a 2.5 minute warmup session and the difference could very well be rounding or other sort of artifact.

NP can’t be less than avg power unless it is calculated incorrectly. Basically the higher numbers grow more than the lower ones when raised to the fourth power. If your power is perfectly even then NP=Avg Power

Half 1W and half 2W (avg=1.5W)
Raise to 4th power=1W and 16W
Average (1+16)/2=8.5
1/4 Power (fourth root) of 8.5=1.7