My signature (specifically the PP) as shown by Xert has been consistently incorrect. The PP power as shown in my sig is over 150w lower than what I have actually achieved in Xert workouts. So, a week ago I attempted to manually create a signature by inputting three best powers on the Calculator page. I entered three recent best power/times, and then saved the signature. It was successful. All three best power/times were now on the new curve, and my signature indicated the correct PP, the one I had recently achieved. But then, after the very next work out, the signature goes back to what it had been, with the PP over 150w lower than what I have achieved in the past. The other two points that I entered were also no longer on the brand new curve. A few days later I attempted the manual process again, with the exact same result.
I presented this issue on the Facebook group a few days ago, starting with the question, “If the PP as shown in my signature is incorrect, then why should I believe the TP value in the signature that Xert calculates?” I also listed the issue I had had with the manual signature creation. Apparently that affected the admin in a negative way, because rather than answers, I was met with what I felt were ad-hominems, stating that issue must somehow be with me, that I was going about getting breakthroughs incorrectly, that I just “don’t get it”, and “Why do you care about PP, you’re 61 years old,” and several other shotgun-type responses, all pointing to me. I also got the customary offer of a “free lesson”. I responded with, “I’d rather have answers than a lesson”, and then was told “That’s your problem.” Rather than respond emotionally to what seemed to me to be an emotional outburst by the admin, I repeated my question: “If the PP as shown in my signature is incorrect, then why should I believe the TP value in the signature that Xert calculates?” Five minutes later I found myself blocked from the group. Apparently I had hit a very sensitive nerve with my questioning and criticism.
So….That’s why I’m asking these questions here. Why does Xert refuse to include in my sig my actual PP as achieved in Xert workouts? Second question, why does my manual input of three best power/time points not “stick?” I have found Xert frustrating enough in terms of the interface, the workflow, and the disorganization of the support articles, but I have come to accept these idiosyncracies. But if can’t trust the Xert signature, that’s a dealbreaker. I want to have Xert work for me, as I am attracted to the selling point that FTP tests are no longer necessary, and I do like the instant positive feedback of breakthroughs, but I do have to feel confident that the estimated TP is accurate.
Just to answer the question as best as I know how:
There are to my knowledge 3 separate forces that can and will change your PP value:
The change in Peak Training Load. If you have done a workout with sprints your Peak TL will go up for a while and then back down again and with it the value of your PP to a degree. You can influence the TL settings in your Account Settings / Profile tab with Training Load Time Constant and Recovery Load Time Constant for the three core systems. I would not mess with that but who knows.
The “artificial” decay Xert applies to all values. I think it is meant to motivate you to do breakthrough workouts to test your values and keep them as accurate as possible. If you don’t want to do that as often and can live with less accurate values you can change to ‘no decay’.
I have and my values are more stable and at least to me look more plausible. PP still fluctuates a lot but I have decided to ignore that and just if and when I do a sprint that actually produces something higher than what Xert thinks at the moment I put the value in ‘advanced MPA’ and click save. HIE tends to fluctuate less but still more than I think is reasonable for my recreational TL state, might be more accurate when fully trained with the higher values being more dependent on TL. There is only so low you can fall when really bad to begin with
Breakthrough or “near breakthrough” (fakethrough, white circle) activities. Where the system thinks it detected a maximal effort on your part and adjusts your fitness signature to fit that maximal effort, up if it is higher (breakthrough) and down if it is lower (near breakthrough). If this was no maximal effort or the power data is incorrect you are supposed to flag the activity to tell Xert to not use it for fitness signature calculation. It will still count towards training load and will as far as I know affect the XATA recommendation for the next days as normal.
Any of those what you were looking for?
Thanks for the reply. It’s interesting stuff and surely good to know…But let me reframe the question a little differently. What good is the PP figure in my signature? A Gold Breakthrough is presumably better than a Silver breakthrough, but if the PP figure in my signature is 150w lower than what I can actually DO every day of the week, what value does the number have in the “fitness” signature? If the number goes up 20w, so what? Now it’s only 130w too low. The HIE I get. It goes up, and now presumably my “battery” is bigger. Same with TP. It goes up in a breakthrough…Yah! I’m more fit. But PP? It’s like some imaginary number.
PP is defined as 5-second max power and is important for sprints and very short duration efforts, so if that’s important to you, you want it to go up and will be happy when it does.
If more endurance focused, having it ball-park correct is all that’s required for other signature parameters to be correct. See @ManofSteele’s response here
As it’s defined as 5-sec power, you shouldn’t be able to put out more than PP for 5 seconds or more - if you do, it’s a BT and your signature is re-set. Maybe you exceeded it for less than 5 seconds?
Not at all!
There has to be some physiological limit on how much power you can produce, no? The traditional CP model completely ignores this fact. And the 3-parameter unfortunately isn’t really an improvement, despite having a Pmax value.
I thought PP was 1 sec max power but the Xert system does not evaluate peaks shorter than 5 sec because they are often erroneous data spikes. So Xert would look for some >5sec sprint and take or conclude the max 1sec power from that to determine PP.
Am basing it on the definitions under key terms here…
OK, thanks! Then where have I seen the 1 sec max power?
Well, you are both right. The article doesn’t fully hash things out.
I PMed Scott and the answer is…
PP = max 1s power (+/- 50 W). It’s very hard to be that precise (also consider that +/- 2% on a PM @ 1200W is already +/- 24 W).
We require you to exceed MPA for >5s in order to get a BT.
So you want to throw down a 5-7 sec all out sprint when fatigued with MPA drawn down and if a BT is detected the signature calc takes over to estimate PP while fresh.
In any case it’s a mathematical construct and I don’t worry about it being my actual max power which physically varies from moment to moment and day to day. Or on some days does not exist.
Ball park is good enough for me.
Ok but practically you need to exceed PP for 5 seconds when fresh… I just created a dummy workout and MPA only drops 13w in 5 seconds riding at PP, which is less than the 50w tolerance and the accuracy of the power meter…
In practice, you’ll find that there’s a bit of a lag between when power is applied and when MPA decreases.
I was referring to BT workouts when you draw down MPA and right before you collapse you jump up and sprint for at least 5-7 secs.
If a BT is detected at that junction your signature will update and if appropriate your PP will change even though you didn’t reach PP during that sprint. However, your performance during that 5-7 secs indicates predicted PP for 1 sec when fresh is X watts.
Here’s an example where my PP rose 30 pts, not from the failed blip to hit PP at the end but from the BT event where indicated which is where the actual 5-7 sec sprint took place.