I’ve been off the bike for about a year until recently. When I left off last April I was the fittest I’d ever been on the bike (248 FTP). My FTP started around 189 after so much time off and is now back up to 207. Not sure if that’s relevant to the question, but there is some background.
I’ve always had a relatively high HR. Touching 200 in a ramp test is not unusual for me. But since picking up training again I’ve noticed a shift in my HR vs RPE compared to a year ago. A year ago HR in the high 170s up to 180 during a threshold session was typical and cardiovascularly challenging. Now I can run HRs into the high 180s, close to 190, at a similar RPE. Could that be related to my relatively low fitness at the moment? Or perhaps more related to how my body’s energy systems are tuned at the moment? I don’t understand physiology enough to make a judgement on what that might mean.