I used to be a runner (and swimmer) as well prior to EFH, and I had the same feeling that I absolutely needed to get my HR up X number of times a week in order to maintain my physical health & fitness. But I had to stop running because I realized it was incredibly stressful for my body, and not actually contributing to my overall health/wellbeing. Now I never run and instead take really long, leisurely walks. And I’ve noticed that removing running and replacing it with walking (which rarely gets my HR up, though occasionally I work up a sweat) hasn’t actually reduced my endurance or fitness! I know this because I’ve gone swimming a few times recently (now that the lake near my grandmother’s house is unfrozen) and I’m just as fast and strong, and could swim for as long, as when I used to run.
I should also mention that I occasionally do yoga, which I think helps to maintain my muscle strength (and probably repair joint damage from all that running). I don’t do the crazy cardio power yoga (though I used to), and opt for more stretchy classes. And if I find myself struggling to breathe calmly and evenly, I rest rather than pushing myself to endure (as I used to do).
I also take long bike rides a few times a month, but whenever I do that I make sure to give myself a few days to recover. I never exercise two days in a row if I feel any muscle soreness anywhere.
To me the main thing is to eliminate the amnt of stress you expose your body to, because that will ultimately harm your wellbeing and inhibit natural healing/repair mechanisms (even if you think it’s clearing out your arteries). Walking requires and produces a totally different mindset, though. It makes you much more chill and observant, which is a good thing for overall health and wellbeing, I believe.
Mix it up and keep it fun! Don’t get too attached to any one thing, lest it become an obsession. It’s liberating to realize you don’t HAVE to pant and sweat and struggle daily (or weekly) in order to get a “good workout” and maintain heart health. You just have to find a fun way to move whenever you want to; keep doing whatever your body is telling you it needs :)