Hi there,
I have an issue where Power Zone data is showing different in Intervals.icu compared to Strava (which incidentally matches the source of the data, Zwift).
If you look at this ride: Zwift - FTP Ramp Test in Innsbruck | Strava
And the comparable ride on on Intervals account (which fed from Strava), the Power Zones don’t match up, with seemingly random times spent in each zone on Intervals. This was a ramp FTP test but for longer endurance rides the discrepancies are even greater as you’d expect.
Any thoughts? Let me know if you need anything else.
Did you set your FTP and Power zones in Intervals? If so, did you set exactly the same as Strava and Zwift?
Hi, thanks for the reply.
Yes, when I was looking yesterday I made sure that my FTP across all systems was 180 and verified this by checking that the zone boundaries were exactly the same as they were on Strava & Zwift. Today the outcome of the FTP test was 243 so I updated this value to both the indoor and outdoor FTP value on intervals, updated it on Strava and verified again that the zone boundaries are the same on both systems, time in zone still off!
Incidentally I also tried adjusting my Strava FTP to the estimated FTP for the ride on Intervals, but that also doesn’t match.
Then you probably have Intervals set to use HeartRate TIZ. Make sure that the TIZ priority is set to an option with Power priority:
Unfortunately it was already set to Power, HR, Pace 
Show screenshots of your settings and the differences Strava<–>Intervals.
It doesn’t help to post a link to your activity because we can’t open that (privacy rules!)
Updating FTP on Intervals takes effect on the next ride after the update. Maybe you just need to set the new FTP on the day before the Ramp Test and then re-analyse your ride. If you want to know what FTP was used for the analysis, use Activity List View with the FTP column.
Ride showing correct FTP used:
Settings (showing correct power zone distribution):
Strava zone distribution (matches Zwift):
Intervals ride summary, showing various different data, including incorrect time in power zones:
Original post says data fed from Strava.
Wondering if it’s due to this. Cos Strava will do some funny stuffs for “privacy”
Delete this workout and upload the original fit file from zwift.
The differences are minimal and caused by different rounding techniques.
Z1: The difference is the coasting time counted in Intervals as Z1 and discarded by Strava. Strava does set Z1 from 0W, so why isn’t it counted??? Total time in Strava is 18:56. Intervals has 19:13 with 17s coasting.
If you add up Z3 and Z4, there is a 3 sec difference. The reason why Z3 and Z4 have the biggest difference in time is that the border between the zones is 243 * 0.9 = 218.7W. Depending on the rounding technique, this can be interpreted as 218 or 219. It’s not like 218 is the end of Z3 and 219 the start of Z4 because then you would discard any value between 218 and 219. Those values go to one of those 2 buckets depending on which border is used.
Z2, Z5 and Z6 have a difference of 1-3 sec, which is to be considered negligible.
To me, none is incorrect. It just depends on how the math is implemented.
Just noticed the discrepancy being debated here thanks to medtechmd.
It’s a few seconds here and there so likely rounding issues.
Do you have workouts where you’re seeing very high inconsistency? Otherwise, what is the main concern?
So I posted about this ride because it was the most recent, but it’s actually a pretty short ride hence minor differences - here is a screenshot of a longer ride where the biggest discrepancy is 10 minutes for Z3, which equates to a 10% difference which is pretty significant in my opinion and means I can’t really trust the data as it’s different from both Zwift (where the data originated) and Strava (which is where I’m trying to verify the data). It also seems weird that if it’s a rounding issue, no one else seems to have mentioned a discrepancy.
Ride in Intervals:
Ride in Strava:
There has been a couple of threads talking about this. I think.
I would test for you, but I don’t have Strava subscriber.
I don’t have Strava nor Zwift myself, so can’t really dig in. But you can easily check out the impact on TIZ yourself by adding/subtracting 1W of your Intervals FTP and reanalysing the activity.
The more time you were riding ‘around’ a zone limit, the bigger the differences will be.
