I am struggling to control my HR at 150; there seems to be a feedback loop operating. My heart wants to beat faster, but it is less efficient so not enough blood is pumped. My body needs more oxygen, so my heart tries to beat faster, but works even less efficiently so lower oxygen etc. until I am crawling along at 200 BPM.
Decided to stick to rollers in near future. Easy to control at 150 on rollers and on the plus side the 25mph averages put me high up on the club’s weekly strava boards.