I am riding 3 times further at a lower heartrate than 6 months age and my VO2 max has not change one bit.
VO2 max changes when you run at least on 70% of your HR max for at least 10 minutes and you improved. And it must be outdoor run, not trail run. This is what manual tells:
The training status feature depends on updated assessments of your fitness level, including at least two VO2 max. measurements per week. Your VO2 max. estimate is updated after outdoor runs or rides during which your heart rate reached at least 70% of your maximum heart rate for several minutes. The trail run and indoor run activities do not generate a VO2 max. estimate in order to preserve the accuracy of your fitness level trend.
To get the most out of the training status feature, you can try these tips. At least two times per week, run or ride outdoors with a power meter, and reach a heart rate higher than 70% of your maximum heart rate for at least 10 minutes.
After using the device for one week, your training status should be available.
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Record all of your fitness activities on this device, or enable the Physio TrueUp feature, allowing your device to learn about your performance (Syncing Activities and Performance Measurements, page 11).
Cycling VO2Max requires the use of a power meter, if you don't have one your cycling VO2Max will not change.
I use one.