Was a post about 20 min power - deleted

Hi Scoob,

Not exactly… that’s part of it, but the sprint (on its own) isn’t adjusting your signature. You should post the breakthrough report, or from the 3.5-4 hr mark on that ride so others can see what’s going on with more detail… it’s quite fascinating, in my opinion. :slight_smile:

Xert determines your signature based on all your efforts - we don’t determine any parameters by looking at “highest avg 20 min power” or “5 min avg power”. As you identified… extrapolating a user’s Threshold from their Peak Power wouldn’t work well at all. It’s very possible to have 2 athletes with a ~300 W TP, but one might have a PP of ~800 W and the other could have a PP of ~1600 W (or more!).


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If you don’t remember suddenly launching a sprint at that point in the ride, it’s a power spike.
If that’s the case you should flag the activity to remove any adjustment to your signature.
Strain score remains. Signature calc is excluded.
Before flagging you can also zoom in and use Previous/Current button to review the BT event.

PP is the least sensitive value in your signature.
See this thread –

I think the point may be that the BT wasn’t just due to peak power / sprint, because of the incomplete recovery from the solid above threshold (red) effort a few minutes earlier, and which used both low and HIE systems, That red effort brought down MPA and it was not recovered to 100% when the sprint happened

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Post your BT report from that activity along with your XPMC chart YTD.
PP is your 1s power. MPA is the limit of your power at any time.
You are verifying your signature as you ride a variety of activities that include over/unders (LTP and TP), max sprints, and intervals that draw down MPA when riding above TP.

You may find these blog posts of interest –
Your Fitness Signature – Xert (
Breaking Through the Xert Way! – Xert (
Fitness Improvement and Day-to-day Variation – Xert (
Understanding MPA – A Story – Xert (

@wescaine was spot on with the assessment!

It’s not just the sprint, but what lead up to the sprint. Xert is analyzing - by using your MPA - that your effort simply wouldn’t be possible if your Threshold Power was 20 W lower - the previous efforts would have sapped too much out of your legs that an ~800 W sprint wouldn’t be possible! If we look at the MPA but reduce your TP by 20 Watts, you’ll see that the highest power you could achieve in that fatigued state would only be ~600 W:

For what it’s worth, MPA analysis also works for your ‘traditional’ 8/20 min efforts as well… you’ll notice MPA will decrease exponentially as you continue holding the effort:

What’s odd about these efforts is that it’s not really ‘natural’… notice all the variation in your original activity data - you never just sat and help ‘xyz Watts’ for the sake of holding ‘xyz Watts’. All those variations in your field data provide far more insight into your performance than simply calculating the highest mean power a rider can maintain for 8min/20 min.

MPA isn’t just a number - it’s a physiological phenomenon that we’ve mathematically modelled with high degree of precision! :slight_smile: If the concept of MPA wasn’t true, then why else couldn’t sprinters run the 400m race at the same speed/intensity as a 100m race?

I think we’re very much in agreement here. For our intents and purposes, Threshold Power is the highest power you can ride at where MPA doesn’t decrease, which I would argue is a great metric for training purposes.

As you continue tracking your training with Xert, you should notice that your signature will respond to your training… train more, and fitness signature parameters will increase. As you reduce training volume, you’ll see your signature slowly decrease.