Running

I don't think that's how HR works. You're trying to optimize a proxy.

zone 5; obviously not safe.

Those posts about your heart and shins exploding if you go above zone 2 are just memes.

Unless you have some congenital heart defect, there is nothing unsafe about sprinting around in z5. You'll just get tired quickly, but not unsafe. Your brain will shut you down before you hurt yourself.

Anyway, your original question... as you get fitter, you'll just get faster for a given heart rate... i wouldnt think of it as lowering your heart rate. (6m/km @ 150bpm, vs 6m/km @ 140bpm)

Think of it as getting faster at a given effort (6m/km @ 150 bpm then running 5m/km @ 150bpm)

you get faster by putting in more miles, mainly. Sprinkle in some fast days, but mostly just lots of slow volume.

So normally just doing more cardio should lower your resting heart rate but resting HR can be very different from HR under load.

One of my colleagues is super fit, regularly does marathons etc, but when she's at pace her heart rate gets up to and exceeds 220bpm. She's seen several doctors about this out of concern and they noted that so long as she feels fine while it's doing this (no pain, not feeling faint etc, she experiences no ill effects) then it's fine. They said her body will let her know if she needs to slow down, it's just how her body is. They had no tips for how she might lower it.

Now I'm not saying you shouldn't be concerned and that you should definitely see a doctor if you are concerned, but if you feel fine while running with the rate you're running at then it might be okay.

My partner runs ultras. She is a slow runner. Longest race 100 miles. I get safety notifications from her fitness watch in the middle of the night that her heart rate is dipping into the high 30s.

Never move, stay inside, drink lots of milk.

Like what others have said: lots of slow volume over weeks/months. It is also about your VO2 max. Purposefully only breathing through your nose (restricted intake, basically) can help with the adaptation like being at altitude. Last time I came back to running, it took like 12 weeks of consistent slow volume to begin to see the HR dip.

I aim to keep my workout rate at between 140-160. I'm 42. This has reduced my resting rate and bp by a good bit. My runs average 30 minutes, when I get above 160 I'll walk till it's down to 120

Keep running the slow miles, building base takes a lot of time, and you'll build a better base with more volume and a few intervals thrown in.

My partner has been heavy into running as cardio support for cycling over the past year, and all the studies she has read basically point to the above (plus better fueling of course).

To begin with, make sure your max HR and zones are all reasonably correct. You say your max is 194, but it's not uncommon for the real max to be a decent amount higher than what you see in regular runs, unless you truly pushed yourself the absolute limit.

I'd use lactate threshold heart rate to calculate your zones, if your hardware/software supports it. Prefer a proper strap over a watch as well if possible.

Beyond that, you're just going to have to run slower than what you are used to, to stay in the lower zones. Try to do it with good technique and reasonably high cadence. If you can't run slow enough, throw in some walking in between to get your HR down.