Wahoo Normalized Power vs Strava

MishMash95

Hey,
Just wanted to pool some opinions on accuracy of wahoo normalized power vs Strava's. My Wahoo normalized power always seems to be quite a bit higher than strava's, especially with high power efforts.

Just did a ride today with a mix of 1-3 minute intervals, and the values reported were as follows:
Strava NP: 269w
Wahoo NP: 297w
Mean avg: 201w

Similarly, last week I did a longer ride with:
Strava NP: 222w
Wahoo NP: 240w
Mean avg: 216w


I tend to find strava's quite representitive, working under the assumption that these numbers are supposed to represent an "equivalent" physiological cost if you were to have done the ride at steady-state, and as I mix in steady-state rides, I feel its quite accurate, and the wahoo just consistently seems around 5-10% too high.

Ultimately I know it means nothing and I can just use strava's, but was curious if anyone found wahoo's estimate to line up, or if it being high is the general consensus. What I would say about the wahoo power is it does seem to better represent my intended "target" power. I.e. when I've done sweetspot rides targetting ~250w, but the avg has been blooped down due to traffic, micro rests, junctions etc; the NP in those cases seems to be an optimistic guess at what I had intended to hold minus the external factors, though in practise, those factors give you a bit of recovery.

Then finally, whether there is any other value in the NP number wahoo kicks out from a training perspective?

Midlands Grimpeur

Are you actually using a power meter? I wasn't sure as you referred to Wahoo's 'estimate'. I use a bolt and have a PM, Strava power readings are always well under the actual readings from the PM/bolt for both AP and NP in my case (generally around 8-10%). I am a bit of a luddite tech wise but have read that Strava and Wahoo use different algorithms to calculate power and from the Strava support forums there are a few people who report lower strava power readings compared to both wahoo and garmin.

I have had my PM calibrated against other power meters under lab testing so I am pretty sure my bolt readings are accurate and the strava one's are too low.

MishMash95

Yeah, using a power meter. Atm, i'm just talking about the discrepency between the Wahoo NP and Strava's Weighted Avg Power. For both, the actual average is identical (as they both just take the mean of the data set), the only difference is in the Normalized power estimates.

I have also heard they use different algorithms, but the main reason I created this topic was just to try and get some insight into the basis behind those algorithms, and given that in my case, the wahoo NP is always higher, whether there was good scientific grounding as to why that might be the case? Or rather, what each number is trying to represent. As I imagine it could be the case that each one is supposedly targetting a different intent, with perhaps Wahoo's NP referring more to the physiological impact of a session, i.e. how much it drains you and generates fatigue, vs strava's which could be more of an indicator of what power you could have sustained for similar "suffering".

Was mainly just interested in whether there was any more information into why the algorithms behave in the way they do, and whether there was research behind it

ric/rstsport

i've no idea which system uses the correct algorithm for calculating NP, but if you send me the original files i'll run them through WKO4 to ascertain what the actual data should be.

cheers
ric

58585

Have a read:
https://support.strava.com/hc/en-us/com ... 1#comments

As far as I can see Wahoo must be using the NP, IF etc as per training peaks algorithms, since they are referring to the those trademarked terms, so I'd be very surprised if they weren't calculated correctly.

Personally I'm only paying attention to the training metrics on TP and not on strava, I've also noticed differences in the TSS/CTL/ATL (strava calls these training load, fitness and freshness).

supermurph09

Do you have your FTP set to the same value on Strava and Wahoo?

MishMash95

Supermurph09 wrote:

Do you have your FTP set to the same value on Strava and Wahoo?

Yeah, they are both set the same. My understanding, however, is that NP shouldn't be affected by FTP, as its just based on the data. I know CTL and IF are affected.

Ric/RSTSport wrote:

i've no idea which system uses the correct algorithm for calculating NP, but if you send me the original files i'll run them through WKO4 to ascertain what the actual data should be.

cheers
ric

Thanks for the input, I downloaded the WKO4 trial out of curiosity and uploaded all of my rides into it. From my quick check, WKO4 gave a reading in the middle of the other two at 285w NP :P! However, the additional data it provides is really useful.

One interesting take away, and why I think WKO4's is potentially the best is that the generated CTL graph seems to far better represent how I physically feel on the bike. As it stands, Strava reckons that my "Fitness" is worse than it was 8 months ago, this seems to be because the value decays incredibly quickly. On WKO4 however, while there are dips that correctly line up with days off the bike, the overall trend is still positive.

So I guess that's a good takeaway from this, really glad to have found out about that software. Should really have known about that before, as I am a bit of a data nut :P