4DP test analyzed in Xert

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Great effort and a nice breakthrough :sunglasses:
Also the recovery sections with the nearly full restore of MPA demonstrates the valid scientific and physiological modelling in XERT and Sufferfest.


I do not quite understand, it seems that the MAP effort was a maximal effort, but does not the graph indicate that the FTP could have been higher as there was still MPA left to expend?

Theoretically yes the end of the FTP section should be where your MPA touches the power. It would take practice and luck to be able to control your power over 20 minutest to completely deplete your MPA. If you hit the threshold with your MPA 1 minute before the end of the test you would not be able to complete the 20 minutes.

This is a copy-paste from a previous response to a very similar question.
Theoretically, your 20min test during FF will be equal to your FTP. If your Xert FTP is set correctly, then by definition, your MPA should not drop at all since you are technically never going “above” FTP. In the same sense, if your fitness signature is accurate in Xert, it should very nearly bottom out at the end of the 5-minute effort. If it doesn’t, the most likely culprits are not having your best day on the bike, or your fitness signature has been created around your outdoor power figures, and you will always see some level of decreased power when riding indoors vs. outdoors. Ultimately Xert and the fitness signature are only as good as the data you feed it, and FF results depend significantly on how good/bad a day you are having.


On another thread , I read that some people use use their bicycle computer to calculate their normalized power during a lap that corresponds to either the MAP or the FF section. That helps them with their pacing.

Incidentally, I modeled my last FF before I did it to estimate my output. Here is the model I used:

Here is where I discuss my results:

With the model and a head unit I imagine you could come pretty close. I am going to try that for my next FF.

There is also a general discussion about Xert and Suf in that thread that might interest you.

Thanks for the information. That makes sense. I haven’t ridden out side for awhile and had been doing mostly sweet spot workouts before trying sufferfest on Wednesday. I think the lack of FTP or above efforts causes my signature in Xert to drop as it was set to normal decay. My calculated FTP in Xert was 248 and my 4DP effort ended up at 265 which is probably why my MPA was dropping for the whole FTP segment.

Perhaps you can adjust your decay setting to “small” in your XERT profile and have a look for your values over the next few weeks.
This worked for me, since I don’t “Stravafy” or “Xertify” my commutes. Also after three weeks without breakthroughs my values are nearly spot on, when I finally crush it.