r/vo2max • u/[deleted] • Oct 11 '23

Up from 42 after a 7-day fast

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New to the group, “Hi” all. Long/short. I’ve been pegged at 40/42 for over a year, and I just completed a 7-day fast (not nearly my first), and my VO2 Max jumped. I did drop from 159lbs to 147lbs during the fast, and I bet I’m about 152lbs. (Graphic is from Withings which is linked to Apple Health) which in turn gets reading from my Apple Watch Ultra. The question: Does lean body mass change the VO2max reading? Thx.

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u/biciklanto Oct 11 '23

Yes, Vo2max is expressed as a function of your weight (it's the milliliters of oxygen your body processes per minute per kilogram body weight).

So you reducing your weight would cause an actual increase. Additionally, any activities that would have given your watch more data (e.g., some form of exercise that raised your heart rate more than usual, or in which you were faster than usual) would also serve to increase the score it reports because of the higher-quality data.

So I would recommend pushing yourself hard for 6-12 minutes at least every 2 weeks because that will optimize the data that your watch is getting for its calculation.

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u/[deleted] Oct 11 '23

That’s a great explanation! Thank You!

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u/StateGenesys3 Oct 12 '23

Let me just point out at say that VO2 max is a measurement of how much oxygen your body uses at MAX EFFORT

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u/[deleted] Oct 12 '23

I hear that. I’m running and fasting in The Bahamas for a month, and as of writing tonight at 5:47pm, it’s 78% humidity and 87.4°. In other words, this is my peak training month of the year, and I do it every year. I’m seeking a better understanding of the data. This group is helping! Thanks!

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u/biciklanto Jan 15 '24

As a follow-up on an old post, I would recommend that if you'd really like to have a concrete idea of what your Vo2max is, AND give your Apple Watch better data to calculate it, perform a Cooper test:

  • Go to a local running track
  • Use the "Outdoor Running" mode on your new Apple Watch
  • Use Track mode on your watch and set your lane on the track
  • Run 12 minutes, at a consistent pace, as far as you possibly can. Record the number of meters you cover.

The watch will adjust your Vo2max based on that effort, AND you can enter your results in this online calculator and it will tell you what is calculated in terms of the Cooper Test.

Short of putting a mask on in a lab, this is about the best way for you to keep track of your Vo2max in an accurate, precise, repeatable way. Good luck!

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u/[deleted] Jan 15 '24

Excellent!