How to initiate VO2max test on Apple Watch?

According to Apple, the Health App calculates the VO max using "the heart and motion sensors during an outdoor walk, run, or hike." It uses information like height, weight, sex ,etc., to help calculate this, so you have to enter those the Health App. Apple says, "It can take at least 24 hours of wearing your Apple Watch, followed by several workouts* and passive measurements with your Apple Watch before you receive an initial estimate." You can see more at

Track your cardio fitness levels - Apple Support

i've been able to trigger a determination of VO2max by going on a walk and tracking it as an exercise. Unless I track the walk, it does not update (for me).

bmk1984, I agree. The graph shows points when the VO2 is updated, and they correspond to dates that I clicked "Add Workout" on the Workout app on my watch.