One of the main problems is that the the VO2Max is kind of a lookup from a data table. From experience I can tell you, that if you do an endurance run, like a GA1 session where you run in a pace that you van sustain for an hour or longer your VO2Max will be very low for that session because pace is a major factor for VO2 Max. However, if you to strides, you will get a much higher VO2Max for that session. Garmin is doing some averaging over these values per session. That’s one angle to look from at the problem. Of you are interested in your session-wise VO2Max, the values are in the .fit files. Runalyze for example does extract and display them.
