Workout - POWER reserve MPA

Hi xertians,
I ran into strange behaviour with xert on my garmin 530.

I was riding the SMART - Blood and Thunder workout outside. All seemed to go quite easy, so I was waiting for the yellow blocks to put in some effort. Expected them to be at about TP. They started out at TP as expected, but then dropped quickly to LTP…
Afterwards I noticed that the power in these blocks is defined as 99,6% reserve MPA. I tried to find some information on what that means but couldn’t find any.
I’ve find something on Reserve MPA in duration though. Xert than calculates the time it would take to bring back MPA to e.g. 60% at a specified amount of power (110% TP) and uses that as duration. If I understand correctly, that duration is than fixed…
So I would think that in this instance, 99,6% reserve MPA refers to the power I have to put in to drop my MPA by 0,4% over 5 minutes. If that value is calculated beforehand, based on my power curve, I would expect that to be constant.

However, it dropped very fast, so it seems to be ‘smart’… Can anyone explain why? I might have put more effort in than required for the earlier LTP intervals, could that be the reason?

I’ve previously had problems with smart intervals outside, but always with the duration. The smart duration time just dropped and a 3min interval was done in 20sec… Frustrating up to the point that I stopped riding xert smart intervals outside as it just didn’t work.
So there might be something wrong with my settings as well, which might explain all this.

Thanks for your time and suggestions!

Doing the earlier efforts would have the entire ‘reserve MPA’ interval ending up way below TP as it would be trying to bring your MPA up to 99.6% of your PP.

What was MPA just before the ‘Reserve MPA’ interval started and what is your Peak Power?

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Here are some references that go into details such as dynamic power vs dynamic duration intervals and much more :wink:

Introducing Smart Workouts – Xert (

Advanced Workout Design using SMART Intervals – Xert (

Are Your Workouts Too Hard? – Xert (

Do you also consider the outdoor advice on occasion and free ride to focus instead of a specific workout?

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Exactly. It’s a SMART interval designed such that at the end of the interval, your MPA is down 0.4% of the difference between PP and TP (i.e. MPA Reserve). If your MPA was already slightly depressed, it’s likely that the interval shifted to LTP, so MPA could recover to 99.6% MPA reserve. HTH!

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Oldmajor & manofsteele, thanks for the suggestions and the clear explanation!

PP 1250, TP 287, MPA reserve 967, so 0,4% is about 4W.
MPA at start of interval was 1249 and did only go down to 1248 in the first minutes in which I put out more power than the smart interval told me to.

Here is the activity: Xert - Activity | SMART - Blood and Thunder

I’ve been hardly riding for about 6 weeks, so my values went down. Yesterday I had a breakthrough, PP went up to 1340, HIE and TP also went up.

However, I’ve ridden a large part of the workout at 105-110% and still found it to be way too easy. And it is rated as difficult. I’ve had the same behaviour with intervals with smart duration steps that finished in seconds rather than minutes. I understand that the values might adapt, but they go down way faster than I would expect…

Ridgerider2, thanks for the references! I searched for “reserve MPA” and found nothing related to power. In the links, it is phrased differently, so doesn’t show up in the search engine…

I sometimes free ride to focus and from time to time do interval workouts outside. But intervals with short steps are difficult outside. And the smart ones don’t always behave like I expect. Still some learning to do!

What is your current status stars count?
How do the intervals feel with your updated signature if you perform the same workout on your smart trainer with the Xert app in AUTO mode?

Also found this article that mentions the relationship between reserve and target power – I just did a workout and some of the intervals were shorter/longer than what was defined in the workout. Why? – Xert (

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I’m at 2 1/3 stars right now, coming from 4 stars two months ago.

My trainer is not set up for the moment, I only ride indoors in winter… I’ll try the same workout outdoor to see how it behaves with the updated values.