so for the longest time xert was showing my ftp around 276, i really doubted i could even do that for 20 mins but i left it…so i did a pretty hard 20 min ride and my ftp was 248…so i inputed that into xert last week and processed my rides…it than put my ftp at 257…ok fine that seemed more reasonable to me. i do some anaerobic work today (same as last Saturday) and it dropped my ftp down to 255…ok so lets say i never changed my ftp in xert last week…it would have brought my ftp down 20 watts? i really doubt it…it is really making me think that xert is not accurate at all!!
Same here, it predicted my tp being 20W too high. I manually entered what I believe to be the accurate value, and the numbers are a lot more reasonable now
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There are for sure others that report similar, also if you search the forum.
Support may chime in but accuracy can be impacted by how much data you’ve fed in and how good quality that is… eg was your high 276 TP estimate from a one-off ride that may have had errors in it? If so, you should flag it so Xert ignores it for signature purposes. In the past I (and am sure others) have benefited from some manual tweaks to my signature, as it also got out of line - actually the other way with too low TP and too high HIE (I suspect from too many BTs with trainer control / erg mode). But I only did that once and since then it’s been fine… the balance between TP and HIE is important to get right, and there is a chart here to check that
Other observation, not sure if you meant it like that, but you said your 20min effort at (I guess) 260w or so was only ‘pretty hard’… so not ‘all out”… which actually sounds normal… 20min at high sweet spot is pretty hard but not that hard. Have you tried riding 20 min at 280w or so (as your signature implies for 20 min)? Riding at 20min power for 20 minutes is meant to be very very very hard - it leads to a breakthrough (ie failure, literally unable to maintain the power) and would only be possible when fresh and super motivated (psychologically those are so tough too)… so on a normal training day with some fatigue you wouldn’t be able to do it, which is also normal
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thanx for reply and the info! its was really close to all out but it also wasnt a steady effort but more of an under/over effort, so if anything i think this number might have been better than what i can hold steady but not much. i definitely feel like im in the area because ive changed my zones to the new numbers. for example ive added 8 min intervals at 255-260 with 2 mins rest between and haven’t been able to get the 4th one yet! maybe the signature still needs some more time to adjust?
I would have thought under overs lead to a lower average power (the efforts above threshold cause a lot of fatigue) but have never tested it…
Could also be other factors like whether the signature comes from outdoor rides while you’re doing intervals inside (where it’s fairly common to have lower power - number of reasons)… or depending on your background, you’re just not used to long steady efforts and how they feel… also 2 min rest is not a lot (and it depends on intensity and cadence of the rest)… so practice 
Over time yes, the signature will decay (assuming you’ve left it on default settings) and you’ll get more breakthroughs and ideally closer to ‘true’. If you are worried you can email support directly and they will take a look.
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I also get the feeling my fitness signature is a bit off sometimes. Especially my TP seems just a little bit too high. I tried to manually adjust it a bit in the past. Which may have thrown the balance between PP, HIE and TP off.
I’m now experimenting with the idea of setting my decay method for agressive decay for a week after my last BT. I will then set it back to default (optimal decay).
a pedantic point though similar Xert does not calculate FTP, however having said that
@xertedbrain asked an interesting question a while back, what is the number you get when you calculate this equation for your signature: ratio HIE*1000/(PP-TP) most people who probably have an accurate signature like Scott and Amando had a number between 30 and about 34.
If it is outside this range it is likely something is off on your signature. It might be that HIE is off or the gap between TP and PP is off. Since PP is usually pretty easy to get from an all out sprint then it is unlikely that PP is off by much meaning if the ratio is over 34 probably HIE is too high or TP is too high.The inverse may be true for a value less than 30?
try the calculation on your signature and let’s hear what you get. It is an interesting question at least to me because I think this calc is a possible diagnostic.
My ratio is 40.3 (PP 911, HIE 25.90, TP 274). My FTP on Garmin is 268 and Strava Est. = 288. My most recent 20 minute max effort is 267 (Not a FTP test- Aug 2021). So TP is likely correct. So does this this mean by PP is off…I have tried working on sprints in the last couple of weeks and moved PP from 865 to 913 (max). Not sure I can get close to 1000+ PP to get to ratio of 30 to 34… but I will continue to try over the next couple of weeks.
If you feel that your TP is right at around 274 then it is likely your HIE is too high, if that were 20.5 or so then the ratio become approx 32 which is in the range.
A good way to see if this makes sense is to go the the advanced MPA chart where you can actually play with the numbers and see how it affects the MPA draw down etc. Choose a near or breakthrough ride file and adjust the HIE to 20.5 and see how it changes the MPA draw down. If it was a true breakthrough or close the MPA should cross the actual power plot at the point of near failure…
Okay, I adjusted my HIE to 20.5, which dropped my 6 min power and increased my LTP but it all looked reasonable. Did an outdoor training ride today got a small breakthrough (increased PP by 1 watt and dropped HIE by a further 1KJ). My LTP increased by a couple of watts to 224 (feels right). Still not sure I fully understand HIE and it’s relationship to TP and LTP yet but I think my Fitness Signature is a better fit now. Thank you for your help!
glad it seems to work but the math is something @xertedbrain (Armando) came up with and the people gave numbers to show the likely correlation. It seems to work though if you have confidence in two numbers the third seems to follow the equation being 30-34 range.
i did some max efforts this week - PP sprint and a 5 min the sprint was 831 and the 5 min 321…it moved TP to 260. so my TP=260 PP= 831 and HIE is 18.9 does this like its lined up correctly now?
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You can also refer to this chart as posted by @wescaine above –
Are there errors in my Fitness Signature? – Xert (baronbiosys.com)
You are looking AOK.
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