eFTP as Master for activities


I use Xert as well as intervals.icu (mainly for training advisor - otherwise intervals.icu probably has everything I need!). With Xert, TP (or FTP) is regularly updated when you achieve a breakthrough, but that number does not feed through to other systems, such as Strava’s FTP value. eFTP seems to be relatively close to Xert’s TP. Is it possible to set eFTP as the master for analysis on all workouts, as opposed to the static FTP value which I only occasionally update?


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The use of eFTP as a single FTP to use for all analysis would not work for me. I need to have indoor FTP applied to indoor rides and similarly outdoor FTP applied to outdoor rides for loading analysis. Perhaps if eFTP changes then people could accept or reject that change to replace the indoor or outdoor FTP?

I agree it wouldn’t work for everyone, but it would be good to have it as a ‘toggle’ option. At the moment unless I constantly tweak my FTP in the system, my time in zones (for example) won’t quite be right.

I have that on the todo list already as an option. I won’t be able to update your Strava FTP, only FTP in Intervals.icu, Strava doesn’t have an API call for that.


Awesome! Don’t worry, no need to sync it to Strava - I use 0 of their analysis tools.


adding to this @david is it also possible to auto-populate the W’ value in settings with the calculated one?


I could use the one from the eFTP curve but that is the same for everyone on the same eFTP. To get a personal number for W’ you need to use “Mortons 3P” on the /power page. You need to make sure you have recent max efforts for 5s, 2-3m and 10-30m. I can’t use that algorithm all the time because if you don’t have good inputs the results are all over the place.

Understood - any idea how xert might do it with HIE?

I don’t know how Xert does it. It is something I want to investigate again. I basically need to be able to figure out automatically when Mortons 3P is producing good results and I can use the W’ number. It should be possible now that I have a reasonable number for FTP (eFTP) to help. When I was last working on this that was the goal, not so much W’.

So single max effort (long enough) provides the FTP information and then shorter efforts are used to try figure out W’ given known FTP.

without being an expert in this at all and no mathematician - would it basically be possible to calculate by using the power curve values above threshold? That would also require some recent efforts, but it can be a smoothed curve anyway. My guess is Xert calculates in this way using recent max efforts at whatever time interval, and then applies a decay factor until it is raised again.e.g. a 5 min best effort increase would see an increase in W’.


Not sure if this is anything you want to pursue, because obviously there’s more to it.

You’d need to read up a lot :sunglasses:

Just in case you haven’t scratched it, HIE is defined here: http://baronbiosys.com/glossary/high-intensity-energy/

That definitely sounds like a possible approach. I am also not a mathematician but fortunately you don’t need all that much maths to write this kind of software.

@Cyclopaat Yes I have seen that. It implies that they deplete W’bal a bit differently but some of the comparisons you have posted make HIE and W’bal look very similar! Xert was my inspiration to try get “FTP estimation without tests” going.


Also, just in, a good explanation on decay: https://forum.xertonline.com/t/i-dont-fully-understand-the-decay-options/34904 (Scott elaborates).

As you can see, it’s a setting like that, which makes it hard(er) to implement…

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Wouldn’t work for me and I wouldn’t want that. Actually, it would invalidate the whole product for me. But as a toggle for people who want it that way - why not.

For what it’s worth - the decay of the eFTP is also something I don’t subscribe to. That may be a very specific concept working only for a very specific training regimen. Or maybe not a very specific training regimen but one which features frequent HIIT stuff and the hunt for high numbers rather than building endurance, a big engine and time to exhaustion. As it stands in that regard the eFTP value is just a thing of mildly amusing interest for me personally. Sometimes glanced over and thinking: uh hu? Yeah sure, if you think so…

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As eFTP seems to be 95% of your 20 min power, it’s probably valid, but less interesting for me personally too, definitely not as a ‘master’. It may look to be similar to Xert’s TP, but it is not.

As a Xert-er, you will have to make sure your power curve is calculated correctly, starting with your PP. Most people get that wrong, which means that TP and likely HIE (W’ - sorta) are off as well.

To set your FTP for Strava or intervals.icu, you should probably look at your one hour power on the curve. That’s not the same as TP for many, which makes sense, considering that FTP is generally your maximum sustainable power for 40-70 minutes, depending on your athlete type, or, as Torsten mentions, your engine and TTE.

Bumping this up. Missing to update manually FTP for me causes more trouble than anything else. Right now I mostly go by my Xert signature as far as workouts go, but for athletes who don’t have/use Xert, having the real time update would be great.

Also you mentioned you can’t fix the one on Strava, what about Garmin connect, is it in their API?

As far as I can tell it isn’t possible to update FTP etc on Garmin Connect via the training or health APIs. I actually had a hard time finding that on the GC website. Found in “per device” user settings.

I was just about to write a new topic when I bumped into this one.
I’m fairly certain my FTP slowly decreased after the indoor season (outdoor sessions tend to be less structured/hard, at least in my case), and I think eFTP is a fairly accurate representation.
Since I very rarely test my FTP during the outdoor season, my FTP stays at the last indoor test during the outdoor season.
I think I therefore underestimate the training load of the outdoor sessions.

@david, do you still plan to implement a way to have the training load (and other metrics) be calculated based on eFTP instead of FTP?

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I am planning to add an option to automatically update the FTP in /settings when eFTP changes. Lots of people have asked for that. Just need to get “custom plots on activity detail page” done and then I will get on that and lots of other small things.


While you’re working on the solution, would it be possible to get an e-mail notification when the eFTP has decreased? I already get e-mail notifications on an increase! @david