Xert MPA question

So since the weather is too good here and the lockdown has eased I am taking break from TR and riding outdoors… Just riding and playing about for now. Loaded up the Xert apps on the Charmin. I really like em (basically display metrics). The fat and carbs consumption is interesting but I have no way to check on its calibration but as a management tool on the road it is pretty good. The thing I am struggling a little bit with is the MPA. This is based on your maximum recorded power output and has a sort of decay model in there for when you are operating above threshold. As soon as this decays to the point where it matches your current power output the theory has it you are done and it is all downhill from there.

Has anyone used this much? I am sort of seeing very few episodes where I even approach within 50 watts of that point in any of my quaisi-structured intervals, but I still feel done. Is it just me…? should I just HTFU and hold on until that point? Is it your classic VO2max margin loss through under-use? As I said I am just riding for giggles ATM, so I may try to explore this over a couple of different style intervals… (Threshold, VO2Max)… just to see. I was just wondering if anyone else has used it in anger.

I used Xert for about 6 months or so (3 years on and off) and struggled to drain the MPA to a level where I would be awarded a breakthrough. I would imagine this is owing to a rubbish W’/FRC/Anaerobic battery - which the Xert algorithm overestimated.

You’re not alone.

I really want to like Xert, but at present there are too many niggles for me to commit.

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  1. Make sure you connect your phone to your garmin so that you are getting Xert signature updates regularly.

  2. It is way harder for me to exhaust MPA outside than it is inside. It takes an extreme amount of focus to work that hard and when you’re inside, it comes more easily.

  3. If you are “Just riding and playing about for now” you won’t hit MPA. It’s really tough to do!

  4. When I did exceed MPA and get breakthroughs, it was never in the beginning or middle of a hard interval workout. Always towards the end of a consistent smasher.

  5. Even when you DO exceed MPA, keep pushing it for another 15 seconds or so. If you just tickle it for a second, you may end up with a near breakthrough, which is Xert’s way of saying “we see you tried, but you didn’t do as much as we thought you could, so we are adjusting your signature down”

I really like the Xert IQ fields, and when you’re training specifically, they can be excellent. Right now with malaise about the state of the world taking a toll on my ability to push hard, I am not even coming close to a breakthrough so I am not paying any attention to them.

Especially if you’re outside - using a Garmin, there is a degree of inaccuracy, resulting in a “fakethrough”. There was a recent Xert podcast on this.

Fair enough; both Xert and Garmin seem to be fouling up their metrics with me. I think it is just that I spent the whole time on TR the last 6 months. Only some z2 stuff outdoors (or Zwift/Tacx). I didn’t use the 530 while on TR so it hasn’t got all that first hand data only the imported stuff. Xert imported a years worth of data from Strava but again I suspect the good stuff is lacking. Either that or I have been overly structured with TR… Never pushing the limits in the ways you do on the road. For example when do you do a max watts sprint in TR? Yet that is one of the Xert signatures. Xert had a really poor handle on my signature when I started it and the first ride outdoors was just me doing the puppy in the garden thing. I got a gold breakthrough. Now every other ride outdoors is giving a bronze one. Mostly on the max power as I have taken to doing a few sprints for the sheer joy of belting down the road. Once on FTP as I was rabbit chasing. It’s just a bit odd to have put in 3-5 minutes at 120% FTP (based on the Xert FTP which is +7 watts up on my last TR number) and not see much of a reaction from the MPA… Glad it isn’t just me being a weed. I did notice that on that one time where I did get an FTP breakthrough the decline was precipitous. So the MPA edged down a bit then fell off a cliff. Perhaps they need a more non-linear metric. Like a power law on MPA margin.

I used Xert for a year and found the opposite to be true.

It’s a model of anaerobic capacity. Models can be wrong. Like you said about pushing for another 15 seconds, you may have more to give than the model predicts. I quickly removed the MPA field from my Garmin 520 for that reason. Go out and do hard max efforts, don’t throttle them by power or HR or MPA.

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I hear ya… but living well is the best revenge

Doing structured training and z2 outside? Doesn’t sound like you were doing max efforts, that is a problem in Xert land. I’ve been dual recording TR workouts on my 530 and TR app, feeding the Garmin/FirstBeat models, and those model outputs look good.

MPA does not reduce linearly with time spent at a specific wattage above Threshold Power - it is not W’ Ballance.

Here’s a recent test I did at 20 minute power in Xert:

and the same test showing W’ Ballance (green line) from Intervals.icu:



Xert has revolutionised training/riding for me, and MPA completely changed the way I’ve paced races. Xert needs a lot of data, and frequent high intensity efforts to properly work out a fitness signature. But once it’s got the data it needs, it is frighteningly accurate.

There’s some really helpful articles online about how to interpret and use MPA. When you are riding at LTP you’re not going to deplete MPA, but once above TP it does begin to deplete. The power number on your Garmin will also change colour as MPA depletes. I paced a hill climb and a Crit with MPA last season, and was able to ride for 40 mins well above what I’d have predicted FTP to be from a 20 min test, and spot on what Xert estimated for TP. Remember FTP is not the same as Xert TP.

If you want to get a breakthrough, you need a steep two to three minute climb and go at it full gas. The sprint the final 15 - 20 seconds. Guarantee you’ll be on your knees afterwards, but likely rewarded with a gold breakthrough. To give you an idea of the efforts required last gold breakthrough required 2 mins at 7.2Wkg with the first minute at 10W/Kg and the final 15s at 13W/kg. That increased TP, MPA and HIE.

I’ll not be able to hold TP for 1hr, but can do the same TP power from 10 - 40 mins.

That looks like a pretty perfectly paced 20 min test!! Great job!

Not really, that was in ERG at 20 minute power for 25 minutes…

Got a decent breakthrough though!


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Yes. Both Xert and WKO models need to be fed with frequent max / high intensity efforts,

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That’s me in trouble then… :netherlands:

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For me too. I’ve gone all-in during the lockdown getting as much volume as I can and keeping the signature fresh with regular max efforts.

Taking the time to understand the system and getting your head round what it wants you to do (or not do) is crucial to getting the best out of it.



Who said anything about throttling.

Even outdoor intervals have been redefined! Who needs five minute blocks when you can do a session like “deplete MPA to 60%”!!!

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A general statement, I’ve throttled hard efforts because of the MPA field (and HR fields) being present on main recording screen. Removing the MPA field from that page helped.

I do love a constant XSSR interval:



That’s not a trivial challenge… for me now though I am just trying to get a good load of data in there with freeform outdoor riding but loosely aligned along 1 vo2max run 1 threshold run per week and a lot of z2 fillers. I have not put in many +3hour rides in this year. I find I need a good few of those to get to the good place, regardless of the higher intensity efforts.

I have found the general documentation on Xert to be quite terse… It has nowhere near the richness of something like TP. So you have to learn by doing really.

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