and @Pirate, yes, it drops as you fatigue. That’s normal. Watching it live is not very useful, IMO, as it really doesn’t mean a whole lot as a number itself. I’m not even sure what you would do with it, as a live number on your screen. It’s not really something you control intently, or has something of more direct significance, unlike power, rpm, etc.
Also Garmin’s FTP estimate will never give you a number higher that what you hit during the ride/workout, FWIW. So, you’ve got to go maximal if you want some movement. But, I leave that to when I’m actually testing and just ignore these FTP estimates all the time. It’s just useless noise, IMO, as I know what I’m targeting or trying to do and for sure it’s not maximal.
PC is going to vary by individual. Mine pretty much drop consistently after an initial rise. I don’t pay it much attention. It also varies day by day and how I warm up. If I warm up with more watts, it starts out higher. Can definitely fudge it, for me anyway, as it takes a good 30+ minutes of high Z3+ for my HR to stabilize and nearly a good hour of high Z2 for my HR to reach a point that I look at for long rides. If I warm up at low Z2 and then hit some intervals, yeah, PC will rocket up some numbers.
I tend to look more for my general HR after X min with certain zones. My big tell, that I pay attention to, most of all, is tempo work and long Z2 work. I don’t reassess fitness (aka FTP test) much at all, but may nudge the range of where I’m working or target higher or lower in the range.
2hr workout with some intervals. Rise during the interval, -2 at the end.
3.5hr workout with 30 min low Z3, the rest Z2. Starts high and drops, HR still well into Z2 for me at that point and doesn’t get to a usable point until after the low Z3 block where HR is still well in Z2. PC is 0 at the end. As I mentioned before my HR won’t really get up until I burn a match or so. Because of how slow my HR responds to low-mid intensity, I really don’t pay much attention until I nail it with some high intensity or the duration is long enough that I think I’ve stabilized. Even if I warm up and do sweet spot, the first block of 92-94% sweet spot is usually still in Z3 HR.
For shits and giggles, here’s a short outside ride that became long because we were drinking. There were a few hills, but mostly a Z1 ride, and a long stop for beer, whiskey, and some trash talking, and then riding on half buzzed. George Thorogood would be proud, maybe, though some guy said he didn’t think guys in spandex drank so much. I’m not sure what this would tell you, but definitely not that I was drinking and biking and half drunk. PC says I was +1 at the end, but I could tell you I was definitely -15 or so. PC hit +5 at the top of the first hill. For me, it’s too short to be anything really meaningful, based on my own knowledge of self.