That doesn't sound right. Even 95% of max heart rate is sustainable for a long, long time. Intervals one can only sustain for 30s are way above VO2max intensity deep in the anaerobic zone. Heart rate pretty much maxes out on those.
90% of maximum heart rate is the start of the anaerobic zone, and maintaining it for multiple minutes requires intense training. If you think you're sustaining 95% for any sort of time then that means you've failed to measure your maximum heart rate correctly.
This really isn't accurate at all. I'm in very strong aerobic shape and 95% of my max heart rate is not at all sustainable for more than a few minutes, and it is also a deeply anaerobic activity. VO2Max != max heart rate. Your heartrate @ VO2 max is typically much lower than your max heartrate. Max genuinely means max in this case, as in, literally the highest you can get your heartrate up. By definition, you are way above your VO2 max in that situation and it is not going to be sustainable for long at all.
Something like 90% approaches what you're talking about, maybe being sustainable for 15 minutes or so, but that 5% makes an enormous difference.
You might be right and my 95% was a bit off. But the main point is that 80-85% being sustainable for only 30s might only be the case for someone who is in absolutely terrible shape.
