Hello DanG_38,
Thanks for using Apple Support Communities. It sounds like you’re having trouble with your VO2 max reading on your Apple Watch. I’m happy to help.
To start, I suggest trying the steps in the article below:
Get the most accurate measurements using your Apple Watch - Apple Support
If that doesn’t help, I suggest making sure that your watch and iPhone are running the latest software versions:
Update your iPhone, iPad, or iPod touch - Apple Support
Update your Apple Watch - Apple Support
Lastly, you may need to unpair your Apple Watch and then set it up again. As long as your signed into iCloud, your Apple Watch will automatically create a backup when you unpair it.
Unpair and erase your Apple Watch - Apple Support
Set up your Apple Watch - Apple Support
Let me know if that helps.
Have a great day.