To preface, I've done a couple of VO2 Max testing sessions with my coach, and from that we have determined my heart rate zones. I did one of these recently, and my heart rate zones changed from when I previously did it (which was when I first began cycling).
The question: my "supra-threshold" HR zone is 161-167 (I have a max HR of 177) and my "aerobic capacity" HR zone is 168-172. In today's race, however, I sustained 166 ("supra-threshold") for 20 minutes and 168 ("aerobic capacity") for 10 minutes. Should sustaining those zones for that long be possible (given the name of the zones), or do I need to tweak them?
Is there a rule of thumb for how long you can sustain supra-threshold/aerobic capacity zones?
FYI I also train with power; I just like the see how they correlate.