FTP and W' J auto-update

Apologies as I think I may have mentioned this before, but I couldn’t find the post.

It would be great if there was an option to have the FTP value and W’J value automatically updated when intervals.icu sees that the current value has been exceeded (or a pop up to ask if you would like to do it). I exceeded both theoretical capacities in a ride last week, but it is a bit of work to update them (particularly the W value) and if you forget, it is then incorrect for future activity calculations.

I don’t do FTP tests (or at least very rarely) so I am happy to go with the intervals eFTP value, and the W’ value will only ever come from intervals data as well.

I am planning to do some more work on W’ soon. At the moment with eFTP just assumes a standard W’ value but I can do a proper job of estimating it using durations too short for eFTP. Then I will look at auto updating.


I think it is very tricky to do it…
From a single random interval, how would you know if your critical power or your w’ has increased? I mean… if usually you hold 350w for 5 min and now you are able to hold 370w for 5 min, which one (CP vs W’) has increased?

I was planning to only look at intervals less than your eFTP minimum duration as a start. So only stuff too short to bump up eFTP. Still it may well be that your CP has gone up and you just haven’t done a long enough effort to see it yet.

I can also look at more that just a single activity for this e.g. when your eFTP goes up look back for a few weeks (months?) and recalculate W’ as well.

So certainly tricky but I think it is worth a try. :slight_smile:

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Scientifically, you really need at least 3 maximal efforts of different durations, otherwise as you said you can’t separate out the contributions of CP and W’. There are technical protocols out there in the literature that would need to be implemented. Yet more work for David!

P.S. I really think that you’ve done an awesome job with intervals.icu, David. If Strava have any sense they’ll buy you out and hire you as the lead developer to integrate it into Strava Premium.


Is there a way to calculate W’J on intervals.icu now? I see the spot to enter it in, but haven’t found a way to run the calculations

Your Power Curve on the /power page will tell you your W’J based on your eFTP



Awesome! @Olly_Thomas thanks for the help!