VO2 and Zwift

[Daniel_Newman2 (Daniel)]

Hi all
I’ve recently noticed that VO2 max forms part of the Category Enforcement in Zwift. My fitness watch (Fitbit) suggests my VO2 is around 47 yet Zwift is estimating at 37.9 which, whilst I’m not the fittest guy, does feel very low for an active person my age (35).

If the data going in is the same (max HR, RHR, weight etc) then does anyone know how the two figures come out so wildly different?

Thanks!

[Colin_Cadden (Colin)]

It’s Zwifts own determination of VO2 max, called zVO2. They were warned on this forum that using this would cause confusion and should, at the very least, rename it, but just wouldn’t listen.

[Released December 2022] Critical Power Information in Zwift Profile

I’m most interested in the word ‘determine’ which I, possibly in error, take to mean calculate. Is there any chance you could tell me how you determine your best estimations of zFTP zMAP VO2max (I wonder whether for consistency this should be zVO2max ?)

[Daniel_Newman2 (Daniel)]

Hi Colin
Thanks so much for taking the time to reply - well it managed to confuse me so people were right! It just seems so wildly off, gave me a complex that I was even less fit than I thought!
Thanks again
Dan

[Ian_Attoe (Ian)]

There are so many different methods out there for calculating VO2max using power, HR, weight etc that very few if any of them provide exactly the same answer.

However you don’t really need to worry, from a Zwift perspective, as having introduced it they have now decided to remove it.

This link gives you latest, I think, info on Category Enforcement:

Category Enforcement Update - Weight Changes [December 2022]

Hi racers, We’ve caught wind of a way to gain an advantage in races related to user weight to lower the recommended category in the category enforcement system. This problem cropped up after we changed the frequency and timing at which the user metrics are calculated and was initially overlooked by…

And if you want short version this is key section:

2. VO2max

With the changes mentioned above, it didn’t make sense to keep using the VO2max value for the category determination for two reasons:

1. Because VO2max is a metric that already includes weight normalization, it uses the weight currently set in the user account. It is also calculated at the same time the other power metrics (zMAP, zFTP) are. Continuing use of VO2max with these changes would cause inconsistency with the weight average that will be used for the category enforcement moving forward.
2. The use of zMAP - a proxy of the user’s maximal aerobic capacity - allows us to discontinue using VO2max in the category determination.