If you, too, watch your Garmin VO2max number slide down as the temperatures climb, you're not imagining it, and you're definitely not alone. How to fix your VO2max trendIf you understand what's happening and you're fine ignoring the number for a few months, that's my recommendation. In the Garmin Connect app, you can go into an activity profile and turn off VO2max calculation for it entirely. Simply copy your existing Run profile, rename it something like "Hot Run," and disable VO2max calculation on that copy. The bottom lineA dropping VO2 max number in the summer is one of the most common false alarms in the running world.