My calculated VO2 Max value has been steady at 53-54 for several weeks. A couple of days ago I looked at the HR zone settings on Garmin Connect, and saw that my Max HR was set at 175. I'm not sure where this value came from, as I'm 62 yo. I changed Max HR to 162 (about what I think I've hit as a true maximum in the past few months). After today's 4-mi tempo run (137 bpm avg / 152 bpm max), my VO2 Max value dropped to 52. I'm thinking the VO2 dropped because my actual HR was a higher percentage of the new Max HR, which was interpreted that I was working harder but was not any faster than normal. BTW, I use the chest strap.
Am I thinking about this correctly?
Thanks - DW