On my series 6 Apple Watch, my VO2 max was 37.5. When I switched to a series 8 Ultra it immediately dropped to 21.6. My exercise routine is the same (3 hours/wk of strength/core, 3 hours/wk of cardio). I believe that the Ultra is in error. What do I need to do to fix it? Thanks.
Apple Watch Ultra
As already mentioned by Jeff Donald, the Apple Watch/Health App can only estimate your VO2 max, if you start a Run-, Hike-, or Walk Outdoor exercise.
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It can take at least 24 hours of wearing your Apple Watch, followed by several Outdoor Walk, Outdoor Run, or Hiking workouts* and passive measurements with your Apple Watch before you receive an initial estimate.
If the Health app detects that your previous cardio fitness estimates could be more accurate, you'll have the option to update your data. In Cardio Fitness, tap Update under Update Your Data. After you update, the Cardio Fitness Data Updated notification shows you the results of the update and how your estimates changed.
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copied from: Track your cardio fitness levels - Apple Support
Your Apple Watch gives you a cardio fitness (V02 max) estimate by measuring how hard your heart is working during an Outdoor Walk, Outdoor Run, or Hiking workout in the Workout app.
>>To estimate your cardio fitness level, your Apple Watch also takes into account your:
Track your cardio fitness levels - Apple Support
Use the Health app on your iPhone or iPad - Apple Support
What workout are you specifically doing, Outdoor Walk, Outdoor Hike, and Outdoor Run?
You’re welcome.
Your outdoor walks are probably severely lowering your VO2 max. Elliptical is not an Outdoor Walk, Hike or Run. I understand the frustration and disappointment. You can contact Apple using the link below. Apple welcomes your feedback, but regrets they cannot individually reply to comments submitted.
For cardio, I do the elliptical for 55 minutes 3 days a week. Of note, I did 15 minutes on an exercise stress test (calculated VO2 max of 55, while per Health my VO2 max was 21). Thank you.
Series 8 Ultra does not seem to be calculating VO2 max correctly
