Using W balance

Not an expert but I have a little bit of knowledge, so here’s my take:

The 2 parameter model works exactly as you would expect - take any point on the curve, take off your FTP and divide by the time in seconds gives you W’. The trouble with that model is that you can’t actually produce the power it thinks you can at very short durations: 10 seconds at 2816 Watts! No chance.

This model assumes that when you deplete W’ at any given power output, you will be unable to continue pedelling which is only correct in one sense: you can’t continue to pedal at that particular intensity.

Now, I’m not particularly familiar with the 3 parameter model, which, as you described, does not follow the same pattern.

Here is a comparison between the actual power curve and the constant work above FTP curve:

They start diverging significantly once you get down to about 180 seconds. It makes intuative sense that you could never output a wattage of 25000 for a single second or 5000 for 5 seconds etc so there is some sort of degradation of W’ in the very short durations.

Less obviously, there is also a reduction in W’ even much further along the curve which isn’t so intuative.

Above I referred to not being able to continue pedalling at the same intensity once you hit the point on the model curve (assuming it is correct), but that doesn’t mean you can’t continue to pedal above FTP, it just means that your ability to continue producing, say 400 Watts is compromised. This is due to being not only being limited by the amount of energy that you can use, but also by the rate that you can use it. In this case you get to a point where you can no longer produce 400 Watts, but can continue to produce 399, 398, 397 etc for a few seconds each until you finally get down to your threshold. This energy is also part of W’ but can never be represented on the power duration curve because it’s imposible to deplete it fully at a single intensity.

Now, I must admit that my knowledge of this comes from learning about Xert and that may well be different to Morton’s model in the exact detail (no doubt it is) but it shows exactly the same sort of ‘behaviour’.

Mike

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There is a good explanation of the Monod 2 & Morton 3 parameter models within this publicly accessible thesis:
https://ssudl.solent.ac.uk/id/eprint/4099/

I have played around with calculating CP & W’ from a number of maximal efforts within a single ride (1 min, 3min, 20min - a bit like a 4DP power test) and then calculating CP & W’ using the 2 parameter model and I am happy with the results. It does have the limitation of not being realistic for very short durations but that is an acknowledged model limitation, and there are more complex models that account better for this such as the Morton 3 Parameter model that David has implemented within intervals.icu.

There is an interesting quote within the thesis: “In theory, the 3-parameter mathematical model should result in the most accurate calculation of CP and Wʹ and is often regarded as the criterion method within the literature
(Mattioni Maturana et al. 2018); however, due to the complexity of calculating CP and Wʹ
from this model, it is not often used by coaches, athletes or researchers.”

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Hi, I really like the concept op W’ as a way of eyeball gauging how deep I went during a ride.

I do find it a bit of a struggle, however, to really see how deep I went on the sprints or climbs due to the fact that there are no gridlines.
I think a couple of horizontal lines (every 5 kJ, or maybe every 20 or 25% of max W’?) would work wonders in readability of the graph!

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I assume somewhere there is an IQ app where you can select a live W’ data field??

I use Xert’s MPA :joy: But, there are more; https://apps.garmin.com/en-US/search?q=w’bal&device=&deviceLimit=&appType=&sort=&start=0&count=30

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Great thanks for that. Is this something you have used or only searched for? I have an Edge 520 and a review says it no longer works on this model. I’ve sent a message to the developer but I guess I can install and check it.

No personal experience with it. W’ has been an interest of mine for some time and I learned about this CIQ app several months back. Strange that it wouldn’t support the 520, as I use it on my 1000 without issue and it was released about a year earlier… Will be curious what, if anything, the developer can offer on why the 520 was excluded.

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Try it or try dr Skiba’s - that seems to work with the 520.

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Zac, ref the one you linked to he replied really quickly, just said some people had to reinstall then all was good.

Cyclopaat , I’ve downloaded and installed both and will try them tomorrow once I can work out where the value settings are :grin:

EDIT - settings found in Connect mobile app.

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I have used this connnectIQ data field on Edge520 since shortly after learning about W’ - I highly recommend!

Ah which one William? I have installed both anyway so I’ll see how they perform tomorrow.

This one: https://apps.garmin.com/en-US/apps/6dcfffe5-cd3d-41f3-8ba3-13fa0647b003

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On the trainer now, one of the 2 is showing an error screen. The other says % W’ Bal (Int)

I worked out that it was the Dr Skiba one which didn’t work.

Hello David,
Two questions

  1. Today i changed my W’ value to 24000 w.e.f. 1 Jan 20, now my all rides are showing almost flat graph, which was earlier proper i guess just for that value of 20000 was less.
  2. Is it not possible to calculate W’ for rides without power meter. maybe on estimated power .

Thanks
Ajit

This one isn’t flat … I picked it more or less at random so I think its working: https://intervals.icu/activities/3664143358

Strava doesn’t give out estimated power via their API (and its generally quite bogus IMO) so I can’t do that easily.

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On average for a round trip, provided the wind (direction) doesn’t change, it’s not that bad.

However, it will calculate 400 Watts when you’re speeding at 50 kph with a strong tail wind and you’re relatively pedaling easy. Then on the return, blowing up into a head wind, doing 25 kph, it will calculate 150 Watts.

I did a hard 30 min climb today and ended up at -.6.6 on the W’ scale, I’m assuming either my CP value is wrong or my W’ value is wrong, how do I know which one to adjust?

I set a season best 12 min power on this climb and a bast for the last 42 days so it was a hard effort.

FTP is accurate at 240W and my CP is currently set to 235W (my power chart shows eFTP of 234 and I understand this is going to be relabelled as CP at some point. W’ set at 14600 but power chart shows 19572.

What is your (1 sec) peak power?

I think you should update W’. If you are happy with your FTP/CP then thats it.

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