Fitness Signature Accuracy - Test?

After using Xert for about 3 month and trusting Xert to assess my fitness as I went along I now have the following signature:

TP = 112w
PP = 1230w
HIE = 67.7kJ
LTP = -57w
3+ HrPower 105w


According to the graph my HIE should be in about 21kJ and not 67kJ. How can I test this?

The last 20min test - Elite smart turbo trainer (myEtraining app) gave a Threshold power of 150w.

What Xert workout can I do to confirm which is true - HIE and TP.

Would picking a constant power of say 150w and seeing what happens to my MPA over time be ok?

That signature would be physically impossible. Just look at the negative LTP for example.


I had a look at your data and made some adjustments. I think the progression makes much more sense now.

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Thank you very much for the adjustments. Much appreciated.

Be interesting to see what the adjustments look like.

Peak Power does not seem relative to TP though. I know you might have a massive burst of power but cannot hold it but it does seem wide apart to me.

HIE is quite variable, but the typical range is approximately 10-40 kJ. A value in the 60’s just indicated that the HIE adjusted down (to 25ish kJ), and the TP needed to be adjusted up. So I went to an older breakthrough, adjusted HIE down, bumped TP up a few watts, then let Xert do the rest of the work and extract the new signature.

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The adjusted signature became:
PP = 1222w
TP = 130w
HIE = 16.6Kj.

I had done a 20min MyETraining Test for assessing my fitness a few days earlier to the adjustment which gave my TP at 150w.

Today I set 150w TTE in Xert android which gave me about 14min. So after 14 min I made a brakethrough.

The question is is 150w or 130w more representative of my TP. Hoping that knowing a more accurate TP would lead to a PP and HIE that is accurate.

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What did you do at the end of the 14 minutes? Did you push yourself to the point of failure?

No I did not push myself to the point of failure at that point, so I presume 150w is still low and the 130w suggested by Xert is too low.

Next is to edit in Xert my TP to 150w and let Xert do its thing with PP and HIE then set TTE for 200w and try again iteratively.

Hoping to reach max Power at which I cannot reach breakthrough in the time suggested in Xert and extract an accurate signature from.

If you didn’t push yourself to the point of failure you didn’t get a true breakthrough. Forget about any steady state or ramp tests and follow a XERT workout such as Xert Fitness Test for Breakthrough Version 2 and give it all you have on the interval titled Push a last time.

On a separate day I’d recommend doing a few sprints to get your PP. It’s easier to get a good value if you have a bit of a downhill run or a tailwind.

At the moment I am really trying to get at an accurate fitness signature.

I would think that the Xert Fitness tests suggested would require an accurate fitness signature as a basis for the the breakthroughs but I may be wrong.

If the current signature is too optimistic that workout will bring you to the point of failure which can be used to determine your signature.

If the current signature is pessimistic you will feel that you have something left in the tank. If this happens, give it all you’ve got in the Push Thrice and Push a last time intervals. In the last interval just keep going until you can’t go any longer and then try and hang on just a bit more.

Alternatively, hit the road and do some STRAVA hunting, or smash the climbs on a rolling section of road and sprint for the top of the last climb. Or do a race. It really doesn’t matter what you do as long as you get to the point of failure.


This wording makes it sound like you’re still hanging onto older methods of “Hold X watts for Y seconds”, which is completely unnecessary when using Xert. In fact, steady state efforts without any variation in the power, especially at the point of failure are more difficult for the system to analyze because it’s more difficult to differentiate the contribution from TP and HIE.

Rather, as expertly recommended by @Old_Major above, you just need to do any sort of effort that brings you to the limit (hard Zwift race, KOM attempt on a local segment, hard push on a club ride, etc. etc.) will be best for determining an accurate fitness signature.

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Thanks for the pointer to the Xert Fitness Test for Breakthrough Version 2 and how to execute it properly. I shall give it a go when I feel up to it.

My current fitness signature of TP = 131w, PP = 1211w, HIE = 23.1kJ now seem reasonable when I check it against the PP vs HIE graph above. Falls nicely within the yellow band from being wildly off.

A question of curiosity: how is the Xert Fitness Test for Breakthrough Version 2 different from the FTP test?.

The Xert tests for breakthroughs are different because they’re designed to elicit a failure point at several different intensities versus 1 steady effort, since Xert is looking for patterns of fatigue rather than taking percentages of MMP. This is because two different types of athletes can generate the same amount of power over 20 min (which would give them the same traditional FTP), but have very different fitness signatures. Using a traditional, constant power 20 min test would make it difficult for Xert to distinguish their fitness signatures, whereas bringing them to failure at multiple different intensities will make it easier to identify each athlete’s own fitness signature.

The “tests for breakthroughs” aren’t always needed…you can always aim to push for a breakthrough during regular interval training if you’d like. Or doing a Zwift race. Or trying for a KOM/PR on a local Strava segment. We leave it up to you!

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Thanks for the clarification. Much appreciated.

what if i want to try the “under pressure”? I’m struggling to see the difference other than the difference in XSS. Maybe a test should be done such that the XSS reflects something closer to what i’m used to doing on that given day?

That is certainly another option.

The critical part of these tests is the part where you see the MPA decreasing until you breakthrough/fail. After that you could just do a light warm down if you want the ride to have a lower XSS.

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I did the version 2 test on Saturday, I feel like there’s a good chance i forgot that I could try to just keep going. I was watching the interval timer and just shooting for maximum effort for the time interval allotted. I have no idea if i could have tried to just keep going (even if at a slightly lower power).

Would it have effected the signature result if i had just kept pushing myself to go as hard as possible despite the power probably being lower than the beginning of the interval?..Now I want to repeat it. sigh
I guess what really confuses me is how do I know when to call it quits during that last interval? I imagine my body will force me into recovery, but my mind can tell my body to keep going as hard as it can, even if “as hard as it can” is only 80 watts.
here’s a picture of my breakthrough workout… the critical part anyways…

Well done.

If you can hold just a bit longer it will either result in a superior signature and/or you will see the MPA and power levels touching each other on a downward slope. If you see the phenomena it’s a pretty good sign that your signature is dialed in.