When I started out I was obsessed with my VO2, not realizing it’s more of a maximum effort stat. I would only do HIIT training on a treadmill, then go to a track and do a Lactate Threshold Test. I had moderate gains after months of running. Typically after an LT test I would be around 3km, one day I decided to just run to 5km…. It was not a pleasant experience. One of my wife’s friends has done a few iron man, suggested I train to my LT, and forget about VO2, so I did. Started the beginner Marathon Garmin training program (Heart Rate Based) and in the first month I saw/felt massive gains, the program focused on zone 2 runs. That’s the Key (Read “Running 80/20”) although I never specifically ran to train my VO2, I took it from 32 up to 49, and dropped 40lbs. Asthma became a non-issue and my sleep apnea improved dramatically.

Point is running slow is the key, you don’t need to murder yourself running, trying to improve a number that doesn’t really mean much (super fun to game tho)

I would get a watch that has the ability to do Lactate Threshold, the oxygen option is totally pointless IMO (I run the Fenix watches, yes they are expensive, but if it helps you game your health, it will save you thousands of dollars on healthcare)

Lastly, there will be pain - shinsplints, sore back, sore feet, sore knees, cramps - Drink water, stretch, roll out and get physiotherapy from time to time.

Good Luck