W' and CP settings help

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?

Intervals.icu uses the differential algorithm. Here is the code that computes it:

let wb = wPrime
let pt = 0
for (let i = 0; i < data.length; i++) {
  let t = time[i]
  let secs = t - pt
  let deltaW = cp - data[i]
  if (deltaW > 0) {
    for (let j = 0; j < secs; j++) wb += deltaW * (wPrime - wb) / wPrime
  } else {
    wb += deltaW * secs
  }
  data[i] = Math.floor(wb)
  pt = t
}

I found a nice writeup here:

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Good to know, thanks @david. This setting is configurable in the Garmin CIQ app so that now the W‘ Balance shown on the Garmin screen should closely approximate what I’m seeing in intervals.icu.

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Great point, this could be the resolution to my query too. I also just realised I was on smart recording, I had to reset my device a while back and never changed it back to 1 sec.

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Tested the new setting this evening. My icu chart is now pretty much identical to my Golden Cheetah one.

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Sorry for bringing this back but wanted to avoid starting a new thread.

Is W’ calculated on the power page from the eFTP or from your inputted FTP? Or have I misunderstood and this doesn’t matter?

Thanks.

If you have the default power model selected (FFT curves + Mortons 3P) then the W’ number is based on the curve for your eFTP i.e. it is the same for everyone with the same eFTP. I am going to be doing some work on automatically estimating W’ from short efforts soon to go with eFTP.

If you have one of the other power models selected then W’ is the value derived from the model. You need to have the right inputs for this to work well.

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which app do you use to visualize your W’Balance on your Garmin?

This is not true any more. W’ is individually estimated by looking at the most energy above eFTP on the athletes actual power curve for the selected duration.

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Here is what I use.

Saying FTP should be “normally be higher than your CP” makes little empirical sense. Its been proven in the lab that CP and CP alone is the point that demarcates heavy from severe boundary, in other words it is the gold standard for the maximal oxidative point beyond which metabolic control is lost. FTP as a power output that can be sustained for approximately 1 hour cannot be greater than CP; you simply wouldn’t be able to sustain that wattage for that long and besides that empirical observation will not even honor the definition of FTP set out in the book TARWAPM (i.e “quasi steady state” maximal power output that can be managed for approximately 1 hour “WITHOUT” fatigue").

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I posted a reply then realised I misread your comment!

So here’s a new one.

It all depends on how you define the parameters / test inputs for these two metrics. Depending on selection of test inputs for CP and means of estimating FTP, FTP may be higher than CP or may be lower. If one is defining FTP from a single test (be that 8min / 20min plus scale factor, or long form time trial / time to exhaustion effort), and includes that effort in their CP calculation, CP should be lower than FTP due to the asymptotic nature of the CP model (and you can’t get test data at infinite time). And of course if define CP from just short tests, and define FTP from one long test, they are likely to be quite different, and as to which comes out larger I think is dependent more on the athlete type (anaerobic or aerobic biased) than anything else - besides the poor selection of test values / model inputs that is!

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I’ve read somewhere that a single 3 min max test is a very good value for CP but it needs to be max throughout, no pacing, so the power curve for the 3 minutes looks like a power curve, high to begin and fading away.

Yes I’ve read that too - a difficult test to do though as I think you need to be very motivated and “honest”! Would be easy to underestimate CP if back off too much after the initial strong effort, or overestimate if end up subconsciously pacing the effort / trying to minimise the inevitable pain!

You may have read in this open-access paper?
https://www.researchgate.net/publication/260375733_A_single-session_testing_protocol_to_determine_critical_power_and_W

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Yes, it would undoubtedly be very painful at the end.

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The means of estimating something and the conceptual definition are two different things. We should not conflate the two. We have good evidence to suggest CP is the demarcating boundary between heavy and severe intensity domains. If you then introduce something called FTP (which has little research validation) to suggest that it is higher than CP, you’ve now just contradicted FTP and its definition laid out in the book. Riding in the severe intensity regime without fatigue is impossible. Frankly, my interest in FTP is minimal. I just picked up this conversation to correct the conceptual notion that there is a steady state exercise intensity that is even higher than CP. There isn’t one.

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