Recently my Vo2Max score on my watch dropped significantly, from 51-52 to 48-49.
I honestly don't put much credence in this actual score (or most of the FirstBeat metrics), as I use Sporttracks to track my Load/Fitness/etc anyway. But I was pretty curious why it's suddenly scoring me so lowly.
Clues:
I went through a two week period where I didn't do any road runs. This sent my "Load" metrics into "unknown" and then following that I saw the drop in Vo2Max score. I don't see how this could be related. All of my road runs since the gap have been pretty consistent with what I was doing before the gap.
I think I also recall changing my HR zones in Garmin Connect. It had an old HR max that I don't think is accurate anymore, which I changed to a slightly lower number. This adjusted all of my HR zones to the point that most of my runs are now in a higher zone than before. (I don't get that "high aerobic deficiency" message anymore). I think this has something to do with the Vo2Max rating but I can't confirm.
I also wear a Vivosmart which I use as my fitness tracker. When I do a Vo2Max test on that device, it still scores me at 52 which is what I am used to. It's my 945 that is consistently downgrading me.
Does anyone know what goes into calculating that score?