# Why is FTP affected by rider weight in Critical Power Model?



## kreuzberg (Feb 1, 2009)

Hi,
Confused about something. I was looking at the excel table that I found on this blog: alex-cycle.blogspot and I noticed that once you have fixed the time and wattage you can hold for that given time period, if you change the assumed weight (of yourself) the estimation of what power you can hold for 60 min changes as well.
This doesn't make sense to me. If you gain, say five pounds, your FTP doesn't just go up because of this. I know there's probably a simple answer, I just need someone to enlighten me...
thanks!


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## iliveonnitro (Feb 19, 2006)

I'll let the man himself respond. But, in the mean time, where is the excel table on that site?


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## Alex_Simmons/RST (Jan 12, 2008)

kreuzberg said:


> Hi,
> Confused about something. I was looking at the excel table that I found on this blog: alex-cycle.blogspot and I noticed that once you have fixed the time and wattage you can hold for that given time period, if you change the assumed weight (of yourself) the estimation of what power you can hold for 60 min changes as well.
> This doesn't make sense to me. If you gain, say five pounds, your FTP doesn't just go up because of this. I know there's probably a simple answer, I just need someone to enlighten me...
> thanks!


I didn't post an excel file but I may have posted a link to the Monod & Scherrer CP model on the Velofit site:
http://www.velo-fit.com/articles/monod.xls

CP isn't dependent on rider mass, however in that sheet CP is expressed as W/kg, hence when the model uses CP (and AWC) to calculate power duration estimates, it needs body mass. If you enter a body mass in the table at the top for the various max power test results, and then a different mass below, you'll get a different set of estimates than using the same mass.

But if CP was expressed as simply watts, then rider mass would simply cancel out of the equations.

I'm not entirely sure why it was set up that way. It's not my sheet. You'd have to ask Eddie Monnier.

As an aside, I tend to find the CP value alone is a better estimate of FTP than the 60-min power estimated by the model (which is essentially CP + contribution from AWC). That assumes of course the data used as inputs is valid for the purpose.


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