A place for runners.
I can not tell, as I have not stopped from exercising XD
How long has passed since you are not training at that level? Have you totally stopped doing any endurance sport?
what you are doing now may be enough to keep that low HR levels, even without the intensity/volume required for your previous level and may be you have moved from (ie) 41 to 43, an actual increase, but not significantive.
Just an opinion.
I've been through it all. First a stress fracture sidelined me. Then pneumonia. I tried to get back in to it then, but never really did. I was lucky if I ran once a month at that point, but I still did run and cycle sometimes.
Then I got pneumonia a second time, and that one flattened me. I couldn't walk up a flight of stairs without being short of breath for over a year. And then covid hit with work from home, so even when I was keen to start cycling again, there was no work to cycle to. So after that second bout of pneumonia it was probably a two year break before I started to get active again (at the beginning of this year).
Now, I'm cycling and running a couple of times a week, but I'm 30gs heavier than I was at my peak, and my VO2Max is WAY down.
But through all of that, my RHR has only shifted slightly.
High 30s when I was super active. Low 40s when I'm mildly active. High 40s when I'm inactive.
I almost completely stopped running for like 6 years and my rhr increased quite a bit (to about 60). started running seriously again 3 years ago and down to 50 atm. So at least in my case it didn't stay low...