W' and CP settings help


I have my W’ and CP set from values I have in GC and have some recent hard efforts at a few durations, in all honesty probably insufficient to give a fully accurate portrayal of current fitness. I’ve been working from 234W FTP and 14600kj W’.
This morning I did the TrainerRoad ramp test which gave me a 240W FTP and I noted that my W’ chart went down to -4.6 so something is clearly not set correctly. The test gave me a years best 10 min power so I guess I can use this as a good value for the Morton CP curve.

I’ve been a long term Golden Cheetah user but tbh I’ve always struggled with knowing where to set CP and W’.

Is there a chart within Intervals.icu which can guide me or can someone on here kindly assist?

Many thanks


I would say finding realistic values for both is a tricky business and indeed the GC estimator is a good starting point, but in my experience it also produced negative values sometimes. What I would suggest is to try and use a slightly higher CP value than you might name “realistic”, say take your 20 min best power. Then find a 4 minute or so effort where you really left it all on the road and make sure W’ is near 0. Hope this helps: after all, these values are statistical tools for assesment and not something you will write on your wall :smiley:

Thanks. Yes, tbh this is what I’ve done previously with ref to the W’ value, need to nail down my CP value, It’s obviously set too low right now at 232 with an FTP of 240 (previously 234). Trial and error I guess.

If you have recent max efforts of 5s, 3-5 minutes and 10 - 30 minutes you can use “Mortons 3P” on the /power page to get good numbers. Change to that in “Options” and show 42d. The eFTP number on the bottom of chart is actually CP from the model (I should change that label). You can move the marker to 1h to get FTP.

Intervals.icu uses “FFT curves + Mortons 3P” by default and for ongoing FTP estimation because it only requires a single max effort. Morton 3P gives results all over the place if you don’t have the correct inputs.

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Not necessarily, unless you have done a 60 minutes ‘all out’ effort. For most people, FTP is not their real 60 minute power, but somewhere between 40 and 70 minutes.

Most, if not all, FTP tests are done taking a % of a 20 minute, or a 2x20 minute test - that’s not the same as 60 minutes.

Even if you have good 3P values, you still do an estimate of your 60 minute CP.

Perfect, thank you for the guidance.

Yes I’m very much on this line of thinking ref the question of ‘what is FTP anyway’?

Having listened to almost every podcast which Stephen Seiler has ever appeared on I am aware of his view on doing a true 60 min effort, I see the paradox of this implying that FTP = 60 min power when it really isn’t, and have done a 60 min effort in the past but not recently.

What I meant was there is no point having a CP value set to below my FTP as I’d be dipping into my W’ at power value below FTP which contradicts what W’ is.

Thanks for the reply.

Fair enough - I’m all in on Xert, so that looks different at these concepts anyway. I’ve tried to empty my 24 kJ W’ tank by attempting 8 seconds at 3000 Watts, but I failed miserably :joy:


What I meant was there is no point having a CP value set to below my FTP as I’d be dipping into my W’ at power value below FTP which contradicts what W’ is.

Not sure this is strictly true, since the definitions of CP & W’ are intrinsically linked and interdependent (see image), but the definition of FTP is not at all dependent on W’ or CP. It’s just that FTP happens to be quite similar to CP, but FTP should normally be higher than your CP if all those metrics have been determined from good inputs/efforts.

CP and W' determination

I would suggest if using W’ for training but with a preference not to have different numbers for CP & FTP it may be better to use your CP value for FTP rather than the other way around.


OK thanks, interesting. Looking at my 42 day chart of efforts it’s clear that I need to improve the quality of the chart by making some more max efforts at various durations, my 42 day curve is way below the modelled curve. It starts to get close at the 10 minute mark and by 15 minutes it’s on the line.

That value is way out currently as I haven’t done a hard 60 min effort for over 6 weeks, it says 208W and I know for a fact I can do 25 mins at around 255W and as I say, my ramp test yesterday gave me 240. I also can’t believe my W’ is just under 50,000. I installed an IQ app recently and during some hard efforts with it set to 14600 I was getting close to zero. More work to do for me to get the data better.

Um, me neither, unless you are capable of well over 2000 Watts (sprint) efforts…

:grinning:I’m certainly not capable, 801W 1 sec max recently, I’m 54 soon and have never trained for max power so pretty low. In Golden Cheetah I had my W’ at 13700 and my ramp test took me down to 1.0 which seems reasonable. Strangely, and I don’t know how this happened, the W’ in intervals.icu has changed to 32241. Anyway, as I say, I need some better efforts to balance up my power curve.

I mean to move the marker and look at the model power number on the right hand side of the “flag” with the values.

Ah I see so to the right of the black horizontal line to the right of the date at the top of the line, thanks. Still skewed by a lack of a hard 60 min effort.

I’ve been doing some efforts way above FTP recently and been monitoring W’ one the IQ app and comparing what the ICU power chart shows for the ride. The app had me down at zero today after 5 x 1 min intervals at 125% FTP bit my icu chart gets nowhere near that low.

Do you have a reference for that app? I would like to improve this in Intervals.icu. Could you have done a 6th interval?

Hi David, it’s one of the ones mentioned in the other thread recently but not the Skiba one, sorry at work just now so can’t check.

I was doing 3 sets of 5 x 1 min but yes I could have done a 6th interval, it would have been tough but I almost certainly would have completed it as I was hitting and exceeding target power right up to 15th interval.

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It’s called W’ balance (W prime balance)

@david On a related question, how is W’bal computed on an activity? My (elementary) understanding is that there are two commonly accepted formulas for this, “Integral” and “Differential” (explained briefly here https://www.trinakan.com/wp/2016/04/02/everything-about-my-w-bal-w-prime-balance-connect-iq-app/ ) Do you use one of these two approaches, or something unique?