Altitude adjusted VO2 max

Thanks HerbanB, your customer focus is much appreciated, as is your organisation's learning values.  And I don't think you need to defend your own approach. I think I understand the constraints you are working under.  

From my point of view, as a customer - who thinks his 945 is the greatest thing since sliced bread, by the way - I just want to know how the thing works and to know that Garmin (or FirstBeat, it seems) are taking my and other customers' feedback seriously and acting upon it, which you appear to be doing.  I don't want to have to read guesswork from other users.  Looking forward very much to an update on this issue.

I'm in the same camp as mylestomp on this one, though I have a 235.  I'm from western PA but spend 2 - 3 months at a time in Colorado.  When in Colorado, I experience a drop in my reported VO2 max readout.  In PA, my runs are on flatter terrain and (obviously) at lower altitude.  In CO, I run much steeper, more technical trails, and at higher elevation (including the Pike's Peak Marathon).  Consequently, my pace is significantly slower.  My perceived effort is much greater than running at a faster pace back in PA, yet my reported VO2 max goes way down.  I'm 60 and in PA my VO2 max runs around 50 +/-2.  In CO, my VO2 max drop to 40 +/-2.  It seems to me that if the the VO2 max algorithm accurately accounted for elevation gain/altitude, I wouldn't see the drop off that I do when doing steeper runs at altitude. My 2 cents.

Let me see if I can explain this simply but understandably. Compare two people, one from PA, the other from Colo. They both, in their respective states, have a measured VO2 max of 50. Are they the same? Nope. The person in Colo. has more oxygen-carrying blood cells, a compensation, called acclimitization, to the higher altitude. Put that person in Pa., and his VO2 max will rocket up because his blood is loaded with oxygen-carrying cells. Put the relatively oxygen-poor PA. person in Colo., and his VO2 max will plummet in the thin air. That's why athletes train high, race low.

You ask why the algorithm doesn't compensate for elevation. It does, but not the way you think. It compensates for the extra effort needed to climb, and less effort to go downhill. More effort is needed to climb than is gained by going downhill.

Your perceived effort is more in Colorado partly because you're climbing more, but also because you now effectively are operating on a lower VO2 max. So think of it this way. Everyone's VO2 max is correlated to the elevation it was calculated at. Go down, it goes up, and vice versa. Your 50 in Pa. just isn't the same as 50 in Colorado. A watch can't compensate for that simply because there's nothing to compensate (except a wounded ego). Here's another way to look at it. To get a VO2 max of 50 in Colorado, you need an eight cylinder engine. To get the same in Pa., where the air is rich in oxygen, all you need is a four-banger. Now how powerful will that four-banger feel going up Pikes Peak.

Cheers

A VO2 max of 50 means the same thing wherever one is located. In your example, the difference is not whether the person is from CO (where I am from) or PA but rather that there’s less oxygen available for use at the higher altitudes of CO. One other related factor is acclimatization to the higher altitude.

By connecting an external temperature sensor, is VO2 max affected? Surely a very low or very high temperature determines a significant decrease in performance

No external sensor is necessary, but one of the functions of the newer devices is that they do have an algorithm to account for elevation and heat. What Is the Heat and Altitude Performance Acclimation Feature? 

Thanks a lot for your explanation