Run vo2max values stuck?

I think the biggest thing for me is that my vo2max since I have used a HRM+Garmin (2015) to have a vo2max, has changed somewhat often at least weekly.  Sometimes I wouldn't get a vo2max reading in the past or vo2max would go up/down depending on type of workout or non-fitness related sources (heat, cold, snow/trail, hangover, overdressed, wearing backpack, etc).  But typically you could see a trend and key strong Tempo runs would usually provide a good 'accurate' result.

Now... since mid July, I get a vo2max result on almost every run... and it is the same.  warm run... cold run... overdressed hungover a bit....  feeling great workout run.  its the same.  

Even considering that my fitness after running Boston marathon for a solid PR(!)... I was then hurt and didn't run for almost two months after.  It dropped 1 in late-June/earl-July as I returned to running more... then back up after 2wks and now sits at the same.

Very non-typical of Garmin watches to read that way.  I don't recall there ever being an update to Vo2max calculation methods.  I guess I'll have to dig through the change log a bit.

My Vo2max changed from 49 to 50 today after around 5 months of consistent training. Last time I had a 50 was beginning of June. So it's not stuck but the logic behind the calculations may have changed. I don't know if Garmin is disclosing any of these internal details, I rather doubt it. 

I wrote a simple utility program in Python to track the VO2Max as a floating point number. I shows what your watch has calculated in each training session. Maybe it can help you to understand what it happening. More information here: https://github.com/jalbiero/vo2max-tracker.

Credits: The program was inspired by https://github.com/bleenhou/fitparser which was also published in this forum. 

Try Runalyze where can see the detail of the VO2 max from the .fit file to two decimals there, it changes all the time. Its a great source of date and expresses it in different ways to the Garmin Pages.

I did do a suggestion to Garmin to show decimals...

Yes, that's a good idea. The Vo2Max value is changing all the time but you don't see it. After some minutes of your running activity you'll get a reading like "+3" which means that your estimated 5k time has improved by 3 seconds but you don't see the Vo2Max change in Garmin Connect as it's not showing the decimals. I'm at 51 for several days now and had several +x improvements but don't know when I will reach 52. I can just guess. Garmin-Kevin 

Well, I don't know if Garmin someday will display decimals. Why? because the number calculated by the watch (the number that is written in the activity file for the training session) is not what the watch display without decimals. I will tell you what I discover when I was developing and testing the program with my own data: When my VO2Max was 51 for running I was getting floating values greater than 51.0 and lesser than 51.50, At some point in time my VO2Max changed to 52, but the values calculated by my watch were never greater than 51.50 (I though a value greater than 51.50 could be ceiling rounded to 52, but that was not the case). Currently my VO2Max is still 52, and the greater value read from my activities is 51.65. To sum up: IMO the watch is applying an extra correction over the FIT data (based on something that it is unknown to me).  

If Garmin wanted to, they could of course change the display to display decimal values too, it's just a coding issue. They could also add something like an arrow +/- to see the trend or something like a gauge on top to see how far away you are from the next Vo2Max increase, there are several possible options. It's just not perfect that you only see 51 and nothing else, unless you would look into the files directly. In my case, I would be at something like 51,8 or so I guess, my assumption is two more runs or so with a +x value and I'll be at 52.

I gave you an explanation why decimals are meaningless from the Garmin point of view; they applies a correction over the value (or values) got from activities. Of course they could implement something else to give users a more precise feedback about how well their training is going. BTW, don't forget that they have something in that regard: when the training status is "productive", VO2Max could be marked with an upper arrow in Garmin Connect application.
Using my program I will be monitoring my progress in order to understand when VO2Max change for bad or for good. Updates will be posted here (I also use Runalyze btw)