My max heart rate is 186 bpm. 90% of that is 167bpm.
I have managed to hold even 171bpm for one hour.
Am I doing VO2max when doing threshold?
For reference, I tend to perform really bad in ramp test. Last one I got 256 watts ftp when I have recently done 275 w for an hour and 20 mins at 300w; both occasions I felt I could ve squeezed maybe 5 to 10 extra watts.
FWIW maybe my case is not so common this I do not know but 90% of max does not sound too crazy to me.