Xert calculations are incorrect

I was training and doing regular FTP tests and went from 220W to 240W FTP over the course of 4 months. My friends who are Xert users recommended Xert to me and I subscribed. Shortly after Xert showed lots of breakthroughs and TP of 262 and then 285 within a week. Those numbers, as much as I’d like to believe them, seemed too high. My friends explained to me that TP and FTP are not exactly same, however when I tried to do Xert workouts, it was so hard, I couldn’t complete them. After few tries I was not really working out and just rode since the weather outdoors got better. I finally did an FTP test today on a trainer to validate or invalidate Xert numbers. My 20 min NP was 260W for that 20min lap so used 95% of avg power to determine my actual FTP, which was 247W. That’s a HUGE difference from 285W and explains why I couldn’t complete Xert workouts. I have a year worth of Xert subscription and I would like to be able to rely on Xert’s algorithms to get to correct numbers and not fiddle around with intensity % to be able to do workouts. Hope someone from Xert can help with this.

Editing to add more information:

  • My training was on Wahoo Kickr indoors on TrainingPeaks/Zwift by FasCat
  • Many Xert breakthroughs happened once I started to ride outside, using Quarq power meter on my bike
  • I was suspicious about differences in power meter readings and compared the two on zwiftpower and turned out there was minimal 1-2% difference
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Import your data into intervals.icu (it’s free) and see what FTP you get there. Do you use Strava? What does Strava estimate your FTP to be?

Post a couple BT reports from those activities that boosted your TP by chunks.
To do that select Activities, Table, and scan the list for those BTs, click on activity Name, then click on the BT badge icon to generate the report.
Provide a couple names of the recommended Xert workouts you couldn’t complete at 100%.
What athlete type is currently selected?
What is your current star status and TL?
Finally, do your PP and HIE fall into normal range shown on this chart?

intervals.icu showed eFTP 249

Workouts I couldn’t complete were these three:

  1. Cheung CX - Ronnestad
  2. SMART - Highway Star
  3. SMART - Uprising+

Athlete type I experimented with few ones. WKO put me as TT, I am stronger on 10m, 20m, 60m power than on 5s 1m power.

HIE/PP fall into upper light yellow line.

My star status fell from 3+ stars to 2+ stars.

My recent Breakthroughs

So it seems Xert is inflating your TP then. If it were me, I’d just reset from the beginning, see what happens.

Makes sense. Nothing to lose really. Will give it one more try. Thanks.

Just refreshed and surprisingly got different numbers (would assume same workouts would be interpreted the same), still too high though 269W, that’s 20W higher than tested FTP.

Your BTs are in short intense efforts, where errors are most likely. I would suggest yo to flag these activities and see what are your new signatures. If you are satisfied try in the future more prolonged intervals if ouwant to test your TP

Which will be based on your latest FTP test.

I do think that Xert finds it hard to reduce TP significantly. It relies on decay methods which can take a long time. If you are then getting new BT’s based on short sharp efforts that is causing the decay not to kick in.
Once your TP is dialled in I am pretty sure it will match your FTP. In fact if I do an FTP test now I use the TP to tell me what to aim for. No massive movements that way but I am sure I can hit that FTP.

Do a full reset or adjust your TP manually and see how you go.

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Are you combining cycling and running power by chance?

I am tinkering now with what to flag so Xert TP matches real FTP. Feels like Xert should be able to interpret that automatically using appropriate model for “high intensity breakthroughs in frequent succession” as that is the whole point of Xert, to be able to determine TP/HIE/PP. Thank you all for suggestions!. Also this doesn’t look correct either.

I did few easy runs a while back which are on Strava, but not sure if Xert picks them up or how it interprets that data

Same thing happened to me. I refreshed more than once and got some wacky numbers each time, all different. The last time I refreshed I got what I think was a close TP estimate, so now I just keep my fingers crossed and leave well enough alone.

Recalculation takes the currently entered (or calculated) values as the value before your first activity, so hitting recalculate over and over will get you more or less useless results.
It should in theory work when you set values that you think might be right at the start of your Xert data, or maybe something below that to give Xert more room to find breakthroughs.

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Actually, what I think I did was completely reset the account, coming in fresh with my Strava activities.

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Xert uses a feedback process - your XSS calculates Training Loads → your Training Loads (using Signature Decay Method and Breakthroughs) calculate your Fitness Signature → your Fitness Signature calculates XSS.

Hence if you start the process off with the wrong values and there aren’t a lot of breakthroughs to bring it back on track, you won’t get great results. Ideally, you should set both your signature and your starting Training Load accurately before doing a recalc. Repeating the exact same thing helps in honing in on the relationship between Training Loads and your Fitness Signature.

Having all this set up properly is a beautiful thing. You can train and track day-to-day progress with great precision. Read our last blog post for additional help.

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In my case there were many breakthroughs from which TP was calculated higher than it should be. I validated that by taking an FTP test after I couldn’t complete prescribed by Xert workouts at TP it calculated.

Which workouts did you try? (edit … up in another post)

Ronnestad is crazy hard. Few can complete that. Highway Star is a bear too. Uprising+ is the easiest of the three but takes a bit of concentration and trusting the dynamic power recovery intervals. If your TP is overestimated by 2%, these workouts can be a lot harder.

Look for workout difficulty to best match your training status. So if you’re at 2 star status, look for 2 diamond difficulty workouts.

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