# Negative W'ball and how to adjust

**URL:** <https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556>\
**Category:** Uncategorized\
**Created:** [27 September 2022 17:48 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556 "2022-09-27T17:48:33Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![Mario1](https://forum.intervals.icu/user_avatar/forum.intervals.icu/mario1/32/37521_2.png) [@Mario1](https://forum.intervals.icu/u/Mario1)\
**Post date:** [27 September 2022 17:48 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/1 "2022-09-27T17:48:33Z")

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TL;DR: I got negative W’bal values but my calculated W’ is unchanged. How to adjust for this?

Looking at the profiles for my last race this part weekend I see that my W’bal went into the negative zone twice. See graph below. In the past when that happened the W’ value calculated in my power curve would change and I would update the number in my Power settings. This time however the calculated W’ value was unchanged. How do I adjust for this? Is this manual adjustment of W’ value in my settings the correct approach?

 ![image](https://forum.intervals.icu/uploads/default/original/2X/2/2ae82d0006d9ef345bbcf7a0c80767db299e7afa.png)

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**Author:** ![app4g](https://forum.intervals.icu/user_avatar/forum.intervals.icu/app4g/32/41800_2.png) [@app4g](https://forum.intervals.icu/u/app4g)\
**Post date:** [28 September 2022 02:58 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/2 "2022-09-28T02:58:31Z")

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just click the pencil icon next to W’Bal at the workout summary and input the new number.

> [@Mario1](#):
>
> s this manual adjustment of W’ value in my settings the correct approach?

yes. for now it is

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**Author:** ![Mario1](https://forum.intervals.icu/user_avatar/forum.intervals.icu/mario1/32/37521_2.png) [@Mario1](https://forum.intervals.icu/u/Mario1)\
**Post date:** [28 September 2022 09:35 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/3 "2022-09-28T09:35:46Z")

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Which new number? My W’ is unchanged.

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**Author:** ![Olly\_Thomas](https://forum.intervals.icu/user_avatar/forum.intervals.icu/olly_thomas/32/28972_2.png) [@Olly\_Thomas](https://forum.intervals.icu/u/Olly_Thomas)\
**Post date:** [28 September 2022 11:51 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/4 "2022-09-28T11:51:59Z")

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Your current W’ + the vale of your negative W’ value

From the above this would be 15.3 + 4.7 = 20k

The other alternative is to do a FTP test or similar to attain where you are at and a more accurate W’ - eg. could you of gone even harder/had a greater negative W’ value

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**Author:** ![Mario1](https://forum.intervals.icu/user_avatar/forum.intervals.icu/mario1/32/37521_2.png) [@Mario1](https://forum.intervals.icu/u/Mario1)\
**Post date:** [28 September 2022 15:51 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/5 "2022-09-28T15:51:23Z")

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Thank you both for the input. Yes, adding the portion that went below zero to my W’ works. In the past my W’ was automatically recalculated in the power curve when that happened, and I’d use that value. Did something change in the implementation or is this a weird power profile that happens to not update the model? Cheers.

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**Author:** ![Olly\_Thomas](https://forum.intervals.icu/user_avatar/forum.intervals.icu/olly_thomas/32/28972_2.png) [@Olly\_Thomas](https://forum.intervals.icu/u/Olly_Thomas)\
**Post date:** [28 September 2022 15:56 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/6 "2022-09-28T15:56:12Z")

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The W’ is only updated in the power curve when a new eFTP is detected I believe.

As such, the effort you did to achieve the negative W’ probably was not long enough to qualify as triggering a change in your detected eFTP.

What is your ‘minimum eFTP duration’ in Setting set as and what was the duration of the effort above?

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<div class="post-metadata">

**Author:** ![Mario1](https://forum.intervals.icu/user_avatar/forum.intervals.icu/mario1/32/37521_2.png) [@Mario1](https://forum.intervals.icu/u/Mario1)\
**Post date:** [28 September 2022 16:24 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/7 "2022-09-28T16:24:04Z")

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> [@Olly\_Thomas](#):
>
> What is your ‘minimum eFTP duration’ in Setting set as and what was the duration of the effort above?

I think you got to the root of the issue. My minimum duration in settings is 180s. This was a ~40min cyclocross race, with bursts of efforts, but it wasn’t sustained like a more traditional road race. My power curve for the season was updated in the 10-40min range due to this effort, but it didn’t update the eFTP.  
Anyway, I was under the impression that the W’ calculation was based on my input FTP, not the eFTP, but it looks like I’m wrong. I guess there is a lot I don’t understand yet about how the W’ and W’bal are implemented in intervals.icu. Is there documentation anywhere that I can refer to?

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**Author:** ![Olly\_Thomas](https://forum.intervals.icu/user_avatar/forum.intervals.icu/olly_thomas/32/28972_2.png) [@Olly\_Thomas](https://forum.intervals.icu/u/Olly_Thomas)\
**Post date:** [29 September 2022 14:38 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/8 "2022-09-29T14:38:48Z")

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> [@Mario1](#):
>
> I guess there is a lot I don’t understand yet about how the W’ and W’bal are implemented in intervals.icu. Is there documentation anywhere that I can refer to?

I’m afraid I don’t have anything specific but this thread has lots of snippers of info in etc. including the algorithm that intervals.icu uses to calculate W’

> [@Using W balance](https://forum.intervals.icu/t/using-w-balance/804):
>
> Hello guys, I am a French mid pack triathlete passionate on sports physiology and training. I am also a MD. I am curious to implement W’ monitoring during my HIIT sessions. Would you be kind enough to tell me if it’s useful ? Maybe to adjust dynamically intervals like Xert does ? Where should I start my reading then ? I have seen apps on the Connect IQ store since I use Garmin devices and I have seen that there are 2 différents methods to compute the W’ (integral and differential), what is the…

This post from within the thread might also be useful…

> [@W' and CP settings help](https://forum.intervals.icu/t/w-and-cp-settings-help/1155/21):
>
> 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:

[https://medium.com/critical-powers/comparison-of-wbalance-algorithms-8838173e2c15](https://medium.com/critical-powers/comparison-of-wbalance-algorithms-8838173e2c15)

Caveat: info might be outdated…

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<div class="post-metadata">

**Author:** ![BlackTek](https://forum.intervals.icu/user_avatar/forum.intervals.icu/blacktek/32/51102_2.png) [@BlackTek](https://forum.intervals.icu/u/BlackTek)\
**Post date:** [3 March 2025 13:55 UTC](https://forum.intervals.icu/t/negative-wball-and-how-to-adjust/20556/9 "2025-03-03T13:55:26Z")

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Hello,  
is there a specific reason for which we can specify only W’, but not CP? I understand that you use the FTP (instead of CP), that normally are quite comparable. But normally CP is a little bit higher because it’s an effort sustainable over 30-40 minutes (vs 60 minutes of FTP).  
Could it be usefull to be able to also specify CP?

Moreover do you use FTP or eFTP in the W’bal calculations?