VO2Max trend and treadmill run

Thanks for the response. My treadmill activities give me a speed too obviously, amongst many other things, which is based on the movement of the arm while running. As I understand it. There's probably more to it but we can simplify for my purpose here.

What you're saying is that Garmin doesn't think this speed estimate is good enough to be used as a VO2Max estimate, is this correct ?

That is correct. In my case, the speed estimate is far off from my actual running speed indicated by the treadmill, particularly if I run intervals with large variation in speed. If you run at a constant pace, you can get it calibrated to show pretty much correct speed and distance.

Ok, this is fine. I understand the intent.

But now something that I find confusing then.

The immense majority of my cardio sessions are at the gym, and I know that Garmin is trying to estimate my VO2Max after each sessions. I don't necessarily see it on the watch or on GC because Garmin rounds the VO2Max data to the nearest unit and it obviously takes time for VO2Max to change. But, I linked my Garming account to Runalayse, which lets me access the raw data, and I see that the actual VO2Max estimates calculated by Garmin comes with 2 digits, so I can see its evolution with a lot more granularity than on the watch itself.

So, since Garmin's raw data is precise enough to includes 2 digits, why does the trend on the watch exclude indoor estimates: we know Garmin calculates and use them in the end.

(to be clear, my question is purely academic, I'm just trying to understand what Garmin is trying to do, VO2Max trend isn't something I find useful as its level of granularity is low while when Runalyse lets me see the raw data with 2 digits already).

The way I see it (mostly guessing), Garmin measures VO2Max on outdoor runs. It also tries to estimate if your training affects the VO2Max in a positive or negative way. This is used to adjust the VO2Max when the watch has no actual measurements.I had VO2Max 54 on my last outdoor run, but after some time with no outdoor running, it has fallen to 53, since the watch thinks I am not training well enough to maintain 54. There is no line showing, as there is when the watch has actual measurements.

JRKingOfBeer said:

since Garmin's raw data is precise enough to includes 2 digits

I think this is a fundamentally incorrect assumption. Garmin measures VO²max outdoors with maybe 5% accuracy. Without GPS, these will be even less accurate guesses. On a treadmill, it makes sense to set the incline to 1% so that it somehow corresponds to outdoor effort.
Two decimal places are more of an attempt not to lose data during transfer to other systems, but not the accuracy of VO²max measurement.

I shouldn't have used the word "precise". I agree, these decimals can't be "precise". Of course.

My point was that for example after each HIIT session (or sometines instead very shortly after), I'm getting a small bump up in those decimals. Or, after a bad run (like 2 days ago I had to finish limping after injuring my knee lol), the bump was a bump down.

Garmin is calculating "something" here that at least goes in the direction of where I think it should go given my activity. The "trend" of those decimals, which is the purpose of this thread, appears to be correct in my case.

Again, yes, of course, it can't possibly be precise.

If you are interested in vo2max calculation "how it works" - and it is clear, it is only for outdoor runs.

Thanks for the document, I think I saw it posted before a few times but never got to read it. I have now read it in full. Yes it is very intesting.

Questions:

1) page 4: error in MaxHR estimates will lead in error in VO2Max estimates but I'm not clear which way around. If Garmin underestimates my MaxHR (I plug in manually a MaxHR lower than what it is in reality), will Garmin overestimate or underedtimate my VO2Max ?

2) page 7, table 4: aren't taller people at an advantage ? well, they've got longer legs so can - potentially - run faster ? I presume longer legs means more leverage so may mean more O2 expenditure and in the end this may not be relevant ? I'm not sure.

As a side note, Table 2 (page 5) mentions the treadmill based tests. I presume these is at least - if not more - accurate than a test done outdoor with a Garmin watch because there is no wind, the speed is constant and very accurate on that type of equipment etc etc. Do you agree ? I presume these are the Bruce Protocoles and the likes ? I'm doing one of those every year at my cardiologist and the last one - in June - showed a VO2Max estimate of 44. Which was exactly what Garmin was estimating too on my watch at that time, 44.

I've got another question actually about the way Garmin calculates its VO2Max estimate:

3) does Garmin recompute a VO2Max after each (outdoor) run from scratch ? Or does it compute a smaller increment that it adds/reduce to the previous VO2Max calculated ? What I mean by this is, for example my VO2Max is 45 now. If I give my watch to someone whose VO2Max is 65, and this persons goes for a run with it, will the VO2Max calculated by the watch after the activity jump from 45 to 65 ?