On the same topic, my VO2Max estimate according to my Apple Watch was at 50,3 in mid August... since then my perception is that my fitness level has increased, as I am able to run faster and longer distances with less effort, but yet the readings have gone down to 49,4... I can only assume it has to do with my weight loss which went up slightly before it dropped by 2Kgs on average during the past few weeks. Body fat percentage also went down, which implies VO2Max should be higher, but I guess with smartwatches, they don't always get it right.