Intervals.icu now estimates W’ (W prime) or anaerobic work capacity. This represents the amount of work you can do above threshold (FTP). Your eFTP, W’ and pMax (max power for 1 second) define the shape of your modelled power curve.
This is useful for specifying workouts above FTP using % of MMP (mean maximal power) for a given duration. You can see your model curve for various durations on the /power page (click “Options” and tick “Show model power curve”).
Currently W’ isn’t estimated on an ongoing basis and applied to new activities like eFTP. I am working on that. You can get it from the /power page and enter it in /settings to apply to future activities.
This sounds awesome, but I don’t think I fully grasp the impact of it, yet. So a couple of questions:
Am I correct in the assumption that on the /power-page the model now estimates FTP and W’ for both 42 days and season?
Since you state that W’ isn’t estimated on an ongoing basis: how often is it estimated?
Once you’ve implemented the auto-estimation, will that value be used for each following activity?
How is the decay in (e)FTP modelled? For normal FTP-tests, I just assume the number will stay valid until I do a new FTP-test a couple of weeks/months later.
The ongoing eFTP estimate is done on a ride by ride basis using just the data for that ride. A single max effort that is long enough will get you a new eFTP number. If the “number for the ride” is less that your current eFTP then your current value is kept, otherwise you get an “FTP UP” email. You can click the “eFTP” number shown on the ride page to see what the estimate for that ride was. You can also plot this on the /fitness page so see how close you have been getting.
The ongoing eFTP number decays if your training load is reduced. It is difficult to get this part right but it seems a better option than just leaving it as it is. You can add a calendar event to set eFTP to whatever you like e.g. after an injury break or whatever when you know it is too high. Then whenever you do a long enough max effort you will get a new number.
I can’t also estimate W’ from a single activity like that. What I need to do is probably look at your last 90 days when your eFTP has gone up and make a new W’ estimate using your new eFTP.
The /power page estimates eFTP and W’ for whichever durations are selected using all of the data for that time period (no decay or anything like that). So for now you need to look there for a W’ number and enter that in /settings to apply to future activities. You can also tick the “show model curve” option to see how well the model matches your actual power curve.
The power model used for %MMP in the workout builder uses your eFTP and W’ for the last 90 days (configurable on the /power page). So the main reason for setting W’ on activities is to see the W’bal chart.