Forerunner 245 - Max VO2 doesn't update when I use a chest HRM

Hi there, without being able to see any activities it would be hard for me to assume why your VO2 Max isn't updating with the chest strap. One thing I do know is that heart rate tends to record lower on the chest strap then the wrist sensor (not always certainly but in most cases). One of the requirements is that your heart rate has to be at least 70% of your max heart rate for 10 consecutive minutes. I think what may be happening is that you might be running in that 65-75 percent range (a normal easy/recovery heart rate range) and with the chest strap it might be dipping down below that 70% threshold in a way that it isn't with the wrist sensor. Per the article What is the VO2 Max. Estimate Feature on My Garmin Device? the requirements for a run activity are as follows.

Running VO2 Max Estimate

NOTE: Activity must be recorded using the Run activity profile. Trail running is not supported due to the variation in terrain conditions that could lead to an inaccurate reading.

• Running Activity must be 10 minutes or longer in length
• Activity must be recorded outdoors with a GPS signal
• Heart rate data from either a built-in optical heart rate sensor or from a chest strap
• Heart rate must be elevated to at least 70% of your maximum heart rate for at least 10 minutes continuously

Hi, thanks for your response. My HR was at least 70% of max for 10mins however I was using the Trail running setting and appears from your response that this doesn't affect the VO2 max estimate. I understand why this might lead to an inaccurate reading however is there a way to override it? Also what is the benefit of using the Trail run setting? Thanks

The point of the trail run is for circumstances where you know the footing is going to be adverse. VO2 Max estimates can't take into consideration the footing meaning if you run 70% of your max heart rate at 7:00 pace on the roads, but 85% of your heart rate at the same pace because the trail is unstable your VO2 Max estimate would drop drastically even though your fitness hasn't changed it's the conditions surrounding the run that has changed. For example we're based out of Kanas, and it's 6 degrees outside, with 4 inches of snow on the ground. That would be a scenario that I would use the trail run profile if I were to go outside for my run. 

Thanks. I used it because I was running off-road in the snow this morning so get your point now. Appreciate your help with this