VO2 max when going uphill

If you have a watch with barometric altimeter, it should definitely take uphill into account.

Yeah. That's the problem. My watch has an altimeter but when the VO2 max is calculated, altitude doesn't play a role. The only reason I have a high heart rate while running in a relatively slow speed, is because I'm climbing the hill. But the calculator only sees that I'm running slowly with a high heart rate.

Does your watch support the Grade-Adjusted Pace? If so, then it should take in account the terrain profile too. If it does not do it, try using the Trail Run profile and enable VO₂max in the settings of the Trail Run activity.

That's a very nice tip and thank you very much. I have the venu 2 plus. I don't think it supports the Grade-Adjusted Pace. Can you please elaborate? Where can I find the trail run profile?

Sorry, Venu 2 does not support VO₂max at Trail.

Oh bummer... Thanks again trux

When you look at your run in Garmin Connect, does it show the altitude increase? Does the watch show it when you look at the activity there?
Garmin's algorithms have taken up/downhill into account in running VO2max for several years (on watches with barometric altimeter like your Venu 2), so I'm pretty sure it's not the case of algorithms ignoring altitude changes. Something else has to be wrong.
But what are you comparing against? Does running on a flat terrain give you better VO2max?

I have an older watch with no VO2max for trail run (Fenix 5+), so I can't comment on that. But I'm not totally confused the trail run would give any any more "correct" results. The fact is that since running VO2max is estimated from pace, elevation change, heart rate (at least), it's not the "scientific" VO2max (maximal oxygen intake), but rather a number that also depends on things like running economy, terrain hardness, etc. And especially running economy is a factor. So, if you running economy running uphill is worse than running on a flat terrain, that would definitely give you a worse VO2max estimate. I know this from personal experience, since my running economy is definitely worse when I'm running slow. And no surprise, the watch lowers my VO2max after slow runs.

Are you sure that VO2 max is calculated from pace, heart rate and elevation change? If that's true then a slower pace going uphill should not lower the VO2 max values. That's my understanding at least.