Hi there.
Today I did <3h mtb ride including a short breakthrough effort, 5m at 384w (best until then was 382w) and Xert recalculated my signature but pretty bad. My threshold power increased 20 watts up to 338 (it was 318 before) There are no issues with my power meter. I flagged the ride so my signature stays the same. Would be helpful to understand how this can happen. Thanks for your help.
Wow. Nice one. Well done 
I’ve had a similar threshold experience myself (well not similar watts as you’re on Planet Titan with that capability)
I’ve always found (if I test to max) that I end up with 20min being about 80% of 5 minute max. If I remember right, the most common range is between 76% to 84%
(To be clear these are separately tested values, rather than interpolating either from a ride. But a useful indicator.
In Xert it’s not really clear how threshold power is calculated from looking at a ride. This is a good example where an indication could be given from
the ride graph of what portion of the ride generated that TP figure or something.
Unless the algorithm is far too complicated for that.
Unflag the activity, generate the BT report, and post that report here.
While unflagged select the Previous button below the chart, zoom in on the BT section including a bit before and after, and post that screenshot here.
Then flag the activity to remove signature calc.
What is your PP and is it reflective of your actual sprint power? If it’s significantly lower than ‘real’, the algorithm will likely underestimate HIE and over estimate TP.
You can also check this article re potential errors (includes a chart with normal ranges), and this thread re normal ratios between signature parameters
Hi Wes,
thanks for your feedback.
my current PP is 813 and quite realistic and also within the normal ranges when i check the article.
Only other thing I can think of is that you didn’t spend much time at MPA (maximum effort time is probably quite low), and you dropped off the power quite suddenly (not sure if it was a climb or something) which I’ve heard before can cause issues with extraction. For most accurate signature you apparently need to spend more time at / near MPA, and have a more ‘natural’ failure pattern than on / off… but overall agree that if your max 5m in power is 384w it may be tough for TP to be 88% of that…
The support team may chime in here (or you could email them), but for now I’d just flag it
It was on a climb. Actually didn’t had a test in mind but after 1 minute or 2 a thought i’ll give it a try and test my 5m power. I didn’t know that i should have hold longer to get a realistic/better test result. But let’s see what the support reports back. I have reached out to them already…
Thing is - a five minute test is a great measure of VO2 capability, so it’s a really useful marker.
I would expect the algorithms to predict based on what they see (and I think what this thread is saying, that’s what it is doing) but rather than suggest the rider has to keep going for longer, just improve the TP estimation based on available information.
Noted the peak power needing to be right. I’ve had this explained to me a dozen times but (because I’m a bit dense probably) I don’t understand why we need peak power measurements to be able to estimate Threshold Power well enough.
If a rider can produce ‘n’ watts for 5 minutes (plus the added info on what the rider was doing before that 5 mins and after that 5 mins) then is that not a good enough way to resolve TP?
(And of course maybe it is, and maybe it’s all good 
)
What a cracking effort !! Looks like you got that heart rate right up there by the end 
Actually I didn’t say there is a need to ride longer, but a need to spend more time at (or I guess technically near) MPA… in this example the MPA and power lines come together quite steeply and are not close for long… what’s needed is for a more time around the failure level… if you keep riding with power dropping off ‘naturally’ (because you can’t do anymore) you apparently get better results… the effort itself could still be 5 minutes, but you’d need to be at failure at say 4:50 and keep pushing all out for the last 10 seconds with declining power… alternatively you could recover slightly (10 seconds) and then go all-out again which should also increase time near MPA… this is just from what I’ve read previously, don’t know the algorithm details…
While Xert doesn’t claim to strictly model physiology, the simple way I think about it is that for a given short effort (5 min in this case), there is a potentially significant ‘anaerobic’ (probably not strictly the right term) contribution, and the higher your PP and HIE, the greater the contribution (and the lower your TP contribution)… Xert tries so split that out to figure out what is longer term sustainable (TP) vs short term ‘burning matches’ (HIE and PP). HIE and PP are apparently correlated hence important to get PP right, even if the effort itself is not heavily relying on PP
That useful.
Hopefully helpful for the OP. Certainly is for me as in my ‘world’ I’ll regularly hit my current limits on climbs (or on intervals if indoors) and will very rarely still be doing anything other than trying to breathe by the top / end (certainly not pedalling significantly, more likely in a heap in the heather) so that helps me explain my own numbers a bit.
Hi everyone… I can chime in here!
Xert never uses % of XYZ min power to determine Threshold Power. As you’ve pointed out, the actual % will likely be slightly different for each user, so it doesn’t work to assign all athlete’s TP at 95% of 20 min power or 90% of 8 min power, etc. like many other platforms do.
Threshold Power (and Peak Power & MPA) are determined from the interaction of your Maximum Power Available and Power data, especially when you’re right on the limit of fatigue. As Wes mentioned, if the effort is just abruptly stopped, then there are many combinations of PP/HIE/TP that could match that one singular effort to failure, just as it’s possible for many different athletes to have the same/similar 20 min power despite having different signatures (more on that below).
Xert doesn’t think this way, but another way to think about this is that this 5 min effort (~377 W) was nearly 50% (actually 46.7%) of your 1s peak power. Also, at the end of the effort, your MPA could have only gone down to ~380 W, because that was your power at the end of the effort. Since your HIE is only ~14.0 kJ, that indicates that most of that work had to be done by your aerobic system, hence the large bump up in Threshold Power as a result of this activity.
On the other hand… if your Peak Power is higher, than HIE is also likely much higher, since those usually scale directly with one another. With a higher Peak Power (say ~1000 W) & HIE ( ~20.0 kJ), this effort becomes possible with your existing TP of ~318 W:
And again, if your Peak Power was much higher, this same effort would be possible for someone with a TP of only ~300 W:
Hopefully that helps explain the importance of Peak Power when calculating your signature, as well as why it’s helpful to Xert to continue efforts until you physically can’t pedal anymore (or standing & sprinting all out at the very end), rather than stopping abruptly.
As we saw above, based only on the ~5 min effort, there are at least 3 different signatures that could explain this performance!
Hey Scott, that’s really helpful, and I guess as a long time user, I mostly understand. What ‘Maximal Effort Time’ would you look for to have confidence in the new sig?
It’s not uncommon to see athletes get breakthroughs on climbs more frequently. It’s been scientifically shown that some riders can produce more power on climbs than on the flats. I have also seen that some power meters can read a few watts higher while standing (difficult to see this effect unless you’re using our Relative Power feature with another rider riding beside you).
In some ways you could consider standing on a bike riding an incline to be a different exercise modality than sitting on the saddle on flat terrain, in which case it’s reasonable to see differing signatures as a result. In some ways, it’s akin to the difference between riding a road bike and a TT bike. Signatures may not be identical. Xert doesn’t account for this difference automatically since not all athletes exhibit differences.
If you trust your power meter and don’t think you have more power on climbs, then you need to tell yourself that you just did this effort and your signature will need to change. If you stopped abruptly at the end of the effort, the system will try and infer which parameters need to change since the information doesn’t reside in the data directly. You didn’t show the system how your power declines during a max effort. Sort of like determining what your Peak Power is after a 20 minute FTP test. The system can’t know because that information isn’t in your data.
What I always recommend is that you flag it if you don’t believe it and see if it happens again in different circumstances. Try and sustain power during a max effort to gain more confidence in the resulting signature. If the same numbers show up, you’ll just have to suffer the disappointment that your fitness numbers are higher than you think. 
Hi Scott,
thank your for your feedback. Sounds reasonable to me. Actually it could have to do with my PP. I haven’t tested it for a few month. I compared my power curve of 2023 and found an outdoor ride end of December where i had a PP BT of 878w.
As i have not performed or planned PP BT tests since then my current MPA could actually be higher than currently stated. And this would explain the latest TP result out of my last BT ride. Does that make sense?
For now I will keep that ride flagged and try another test to have more confidence in my power and numbers 
