Incorrect FTP determination

A few days ago I did an FTP test and got a new FTP of 321. The next day I checked Xert and it said my FTP was… 269?! I adjusted my fitness signature back to 321 and now it seems to be stuck at 312ish and nothing I do to my fitness signature will fix it. This is very frustrating and I am stuck manually changing the FTP value before I do workouts so that they’re at the correct intensity. My MPA is ~705 and HIE is ~22 (and I’ve been using Xert for a couple years.)

Sounds like invalid data from one ride/workout or another or an unexpected value such as peak power is too low.
How often do you perform BT workouts that test multiple points along your power curve?
What type of FTP test was it?
What happens if you adjust your PP number based on this chart to say 1050?
Are there errors in my Fitness Signature? – Xert (

You can also try flagging any suspect activity in the table view and watch what happens to your signature.
If you can’t locate the cause you can file a support request by contacting and they’ll inspect your data.

For FTP tests I typically follow the protocol here:
I’m a triathlete, so I do these tests every few months and don’t spend a lot of time above threshold in training. I’ve tried setting PP and HIE to every possible combination and the only effect (if any) is that it decreases it below 312. I’ve looked through past workouts and can’t find one that stands out as being incorrect, but I did notice that all my past workouts show an FTP on 271, when at the time it was 290, so Xert has retroactively lowered my FTP on all past workouts.

I guess the problem is the data that is put into the system. For a 320 TP the MPA is very (very, very!) low at 700, even for a triathlete. I mean, everybody is different for sure, but everybody I know personally with a 300+ watt TP has also a 1000w+ Sprint. The two people I know personally with a 320ish tp have even a 1200w+ sprint
I would not fiddle manually with the numbers (messed things up for me too) but try and get some really good 5sek sprints. Really good meaning not just effort but also very good technique. There’s even a podcast episode where Armando explains how he performs max sprints: Small Ring, somewhat middle cog, shifting once or twice when you are spinning out.
Once you are sure you have your MPA set, I would go for another breakthrough attempt.
Most important question to answer for yourself: What do you feel your TP actually is?

My son has an FTP of 335 at the mineute. But his max 1 sec power is only in the low 800w range.

As I said, everybody is different. And I will admit that aerobic fitness and muscular fitness are not the same (though they often correlate in healthy amateur athletes). That being said: I still claim (especially a male between I assume 25 and 35) with a tp of 335 and a 1sek peak of 800w is not the norm.
Well I actually don’t “claim” it: Just look at the Xert’s ranking sheet: Population of xert users median: 1hr/233w, 10sek/807w
Having a 800w max power and a 335tp is not just a little off, it is VERY unusual.
This goes for every other study/data compilation I have found over the last years.

I don’t say it is not possible to have a high TP and low PP (it is very well possible), but you can never rely on an algorithm to determine your training zones and if you don’t fit the norm you have to rely on the knowledge of your own body more than if you do fit the norm (I’m very happy that I’m all the way average btw :-)). And you have to ask more questions like: Why is my TP so high compared to my PP. Maybe there is a perfectly fine reason. But again: More often then not you just fed a not representative PP effort.

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He is 23 and a solid TT rider. His PP isn’t 800 it’s in the low 800s, about 830w.

I suggest you file a request and Xert support will take a look at your data.
I suspect you don’t have enough data points sampled or BT events to generate a proper signature based on how the algorithms work.
I make the effort to force the issue every time a “signature stale” warning appears on the Training tab. That occurs every few weeks, not months.

Take a look at your spider chart under Ranking. How star shaped is it?
Do you set your athlete type (focus duration) to TT or Tri and leave it there all the time?

Reference: Breaking Through the Xert Way! – Xert (

Lionel Sanders, one of the best tri-athletes in the world, has really low Peak Power of 8-900w…

Yes, I’m a big fan of Lionel.