V02 max on GPS watch. Accurate or not?

It may be somewhat useful in reference to itself regarding how your fitness is trending over time. However, it probably is completely inaccurate as a measurement of VO2max. I personally don't really trust most "fitness tracker" stats in general.

Only one metric matters: Race Times.

But if you know you have a solid vo2 max (which I doubt can be obtained from a watch) then you know you need to focus on other stuff (running economy I guess?)

It's an absolute bogus metric. It means nothing. Typically they are based off some wrist based HR which is a completely idiotic way to predict fitness or VO2max. If you want to know your VO2max get a test.

It's not very good if you are actually training. When I do intervals mine goes down as I think it just looks at overall time, mileage, and heartrate. Running hills (I live in the mountains) causes a decline too as my heartrate is way up for any particular time and distance. Thus, if you want a high "watch vo2", just run 4 to 5 every day at the same average pace. This is for the Garmin watch, don't know about the others.

I think you answered your own question, really. The metric can be a decent approximation but works best after a race. Then you'll generally watch yourself get slightly less fit for weeks until miraculously you get fit again after a time trial. As a training metric, it's pretty useless compared to just feeling that the tempo is easier this week than it was 6 weeks ago, etc.

Yeah, my watch VO2 max goes down when it’s really hot and humid. Spikes back up in the cooler months because I can runner the same or faster pace at a lower HR. I think it’s a general guide, but certainly not an accurate metric.

My Garmin vo2 value is typically within 1-2 pts of the vdot values of my recent race performances. Being accurate about your max hr value is important to get the calculator to work properly.

The day to day fluctuations are just noise but when looking at weekly and monthly trends the change in values track pretty closely to both my perceived fitness and race performances. (My Garmin vo2 never varies by more than 2 pts in any week but it has gone up about 8 pts after a year of steady training) I also think it gives a steadier and more useful number than Strava's fitness score which is really just a training load tracker.

If you've been training for 3 months and hadn't done any recent races, taking your Garmin vo2 value , plugging that number into Daniel's vdot chart to predict a possible race time and then maybe adding 5 seconds a mile to be conservative wouldn't be a horrible strategy.

I take the measurements from Garmin instruments with a grain of salt.

I use Garmin hr watch (945) for running and also have garmin equipment for cycling (a hrm strap/power meter pedals/bike computer). The hr watch has my vO2 max estimated at 61, on cycling it estimates my fitness at like a 57.

This is perhaps a bit ironic because at this point in my life I'm a better cyclist than I am a runner. Last year I ran 82 min for a half marathon last year which is alright, but I actually participated in a bike race that was 100 miles and had >500 people in it and finished in the top 35, averaging 23mph for first 50 miles and blowing up a bit to average 21miles for a relatively hilly course after getting dropped from leaders. For cycling training, I'm almost entirely in the z2 hr range, so maybe that's why it's lower? For running training, I am mostly z2, but will do some work in z4 once a week or so.

So that's a longwinded way of saying idk how accurate they are, but my best guess is that it is based on some function of how much you do aerobically + the peak of your hr.

I find it a reliable but not valid measure of my VO2 max

Reliable in the sense that at the same level of fitness I get the same estimated VO@max estimate. And it varies very predictably with my actual race performance.

I find it useful as a Benchmark. It does seem to increase/decrease in response to how my training is going.

But it is not valid/accurate. Let's use my current fitness. I ran a local 5k a few weeks ago and the VO2 calculators estimate a VO2 of 39.7. My Garmin estimates my VO2 max at 45. I wish. :)

In my case the VO2 max measured by the watch and the race time predictions are spot-on within +/- 10seconds....

I use a HR belt for more accuracy in HR reading because I don't think the optical sensor works well when you're running.

So I would say that it's a good metric to watch for fun. If it's trending up, you're probably getting a little bit fitter.

Garmin VO2max: 57ml/kg/min.

Lab testing says 53.8 ml/kg/min.

I have had really good experience with Fenix 5 and Apple Watch with VO2Max estimates.

Garmin gives me 52 ml/min/kg.

Apple gives me 54.

I measured 53 with a consumer portable metabolic cart. Slope of hr/VO2 from a track graded exercise test and max HR gives me about the same.

Cooper test gives me 52.

All pretty close for me. Good enough for government work, right?

If it were accurate, what would that mean anyway? What would you do with that number?

I have turned off the wrist HR sensor on my watch, which also disables the stupid vo2max feature. I don't need the inaccurate wrist HR and I don't need the completely made up vo2max number. Show me the time/distance and shut the f*ck up, stupid watch.

My peak VO2 on watch was 67 despite having run under 8 in the 3k. Garbage metric.

Completely inaccurate.

I haven't followed any recent research in the area, but I think it's a big mistake to treat VO2 max and economy as independent variables, with VO2 max as the key limiting factor that can only be increased a tiny amount. I remember when Matt Carpenter, decades ago, told me that he his VO2 max had been measured as the highest ever (mid-90s) for a runner during testing at the U.S. Olympic Training Center. Matt reasonably asked why he wasn't running world-class times in conventional distance races. He was told (of course) that his running economy must be bad. Matt then reasonably asked what he could do to improve his running economy. The physiologists had no good answers. They suggested that he try running 200 meter repetitions to improve his economy. Didn't work.

Conversely, you can find world-class distance runners with VO2 max numbers around 70ml/kg/minute, suggesting high economy (and probably high lactate threshold). People might think that if you can just find guys with Matt's VO2 max and (for example) Kjell-Erik Stahl's economy and high lactate threshold, then you can develop a bunch of super world class runners who will crush everyone else. But it just doesn't seem to happen. And I've never seen any persuasive evidence that economy can be improved much more dramatically (except through exogenous methods like shoe technology and pacers who reduce air resistance) than VO2 max, despite decades of claims by mediocre physiologists and running journalists and authors.

I look at VO2 max estimates on my Garmin when they pop up. It's not clear to me why really slow jogging can produce numbers significantly higher than those that show up in in much more intense training. But it doesn't much matter to me. The VO2 max numbers are more useful in confirming the extent of my decline in aerobic capacity over the past 35 years or so, especially because of the strong relationship between VO2 max and longevity among the elderly.