Advice on improbably high fitness signature update

I got a fitness breakthrough in a Zwift race yesterday, which was not unexpected. However, based on this Xert has increased my Threshold Power by 22W to 256W. This is not credible. This is not a power I can sustain over any extended period. For reference my Garmin, which also has the benefit of my HR data, increased it to 238W based on the same activity. This is credible. I might have prepared to believe anything up to about 245W.

However, playing with the numbers I can’t make even 245W fit without an enormous increase to HIE.

Given that I simply don’t believe the new signature, how would folks recommend proceeding?

Here’s what the interesting bit looks like with my old signature (PP 892, HIE 18.7, TP 234):

and with the updated signature (PP 896, HIE 19.3, TP 256):

Are you sure your PP is correct/high enough? You could try to set it higher (1000/1100?) and “refresh” + “extract” and see if what comes out does look more realistic. As long as you don’t “save” nothing is actually changed so it doesn’t hurt to try and play around a bit.

I think so. If anything it might be too high. I haven’t managed to hit anywhere close to 1000W in a sprint in a long time, and I’ve tried!

The reason any other platform won’t have the same result is because they’re only looking at average power over the activity… they aren’t accounting for the order in which the work was performed.

I used the workout designer to demonstrate why this is important. I used 2 interval steps to set up the demonstration: 20s at 2 min power and 25 min at 105% Threshold power (using my specific signature - I probably should have used MMP for both so they’d apply equally to all athletes/signatures). The average power for both efforts (and total work performed) between the two are identical:

However, if we look closely at the first setup, which is 20s hard effort followed by extended effort above threshold, the interval ends with MPA close to, but not quite reaching, MPA:

On the other hand, if we model riding above Threshold for ~25 min and then do the 20s effort at 2 min power, we can see that this effort wouldn’t be possible, because of the order in which the work is done. MPA is already too depleted when the hard effort is started to achieve this effort, even if it has the same average power/work performed as the first set:

Most other platforms might simply ~95% of your 20 min average power from that effort, but what that fails to account for is at the very end of your race, your MPA still needed to be high enough that you could ride at 400 W for ~30s or so. If your threshold was lower, then your MPA would already be too depleted for you to be able to achieve an effort of that magnitude.

Hope that makes sense!


How do you know? You could always try when you are recovered, and you may surprise yourself :blush: doesn’t have to be in one go, just do a few long-ish intervals at threshold and see how you get on. It’s a good workout anyway. If you’re absolutely gasping for breath at max HR after 10 minutes, you’ll know it’s too high…

To me the signature looks like a reasonable result relative to the effort


This wasn’t a lone breakthrough. I’ve had a succession on breakthroughs over the last few months, so my signature has stayed reasonably fresh. A 22W increase is improbable on a number of fronts.

If you really don’t like the new number, you can always flag the activity and wait to see what happens on your next short hard effort. Or split the difference and Save/Lock.


Ok, if you think your powermeter is wrong or you forgot to calibrate then as @ridgerider2 says it’s easy to flag it, which will do what you want.

But if there are no power meter issues, you did actually have some very hard hard efforts to bring MPA down, were able to broadly hold (new) threshold power in between those (not easy in general and especially not if you think TP is actually lower), and had enough energy for another very hard effort, well above threshold, at the end… all to say the estimated signature seems reasonable assuming no power meter issues.

P.s. I don’t think Garmin considers HR in its FTP estimate, only average power vs time as mentioned by @ManofSteele. It also likely understimates your ride as he also explained. HR is used for the LTHR estimate though

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@mdbooth first up - massive congrats on the achievement. Whether it’s right or not, you look like you’ve done harder and achieved something - so nice one and may it continue for years :+1:

Is the applications algorithm right for a 20 min power number - that’s much harder - as looking at that picture, am I right (I might be, I’m using the numbers at the bottom), the longest ‘peak’ is about 14 minutes?

It does ‘look’ like (without the actual chart obvs) your threshold power is higher for those 14 minutes.
Have you zoomed in on the peak 14 mins to see what that average was?

You could go and do a traditional ftp test for a giggle once you’ve recovered properly from that race and see what happens. Even ERG it at a suitable number and just focus on cadence ….

Nicely done on your effort

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