I did a 10K "run" this morning - easily, at an easy pace. I wore my el cheapo Aldi Heart Rate monitor and set it so that it beeped at me if I went above 130 BPM and also beeped at me if I went below 125BPM. I am unsure of my absolute maximum heart rate - but I suspect it to be somewhere around 155-160, so the 130 BPM that I set the HRM to as a maximum for the run, should have kept me within the aerobic zone ( below the lactic threshold) .
I discovered that even when running at a comfortable easy pace with my breathing well under control, my HR wanted to go above 130 BPM - so at that point I walked until it fell back to the lower limit of 125BPM.
The end result was a comfortable and easy 10 K training run at a pace of 8:04 per K. I think I will consider this to be my current fitness level at 10K for now and will do this same run once per week for the next month or so (after we come back from 2 week hols) and see how the results change. Eventually I should be able to increase my pace while maintaining the same HR numbers and/or increase the HR numbers a little until I reach a "race" pace.
The last time I did a 10K training run - I did it non-stop at a slightly faster pace of 7:50 per k -- but I was "wiped" at the end of that. With today's run, I was even able to do three 100 metre "pickups" at the very end of the run. I think that I am definitely going to continue with this HRM training over the longer distances once per week, and simply "go for it" for my weekly Zombies Run 30 min and my usual weekly Parkrun .