Hi Carole,
Have your legs recovered from your 1/2 marathon?
I saw a sports physician (don't know what you call him, he's an MD specialised in sports and sports injuries) who did some tests. He said my max HR was 190, which was a little above average for a 42 yo woman. But so was everything else according to him: lung capcity, VO2, body fat%, muscle tone and muscle length and normal heart ECG, don't remember what else was tested.
He said my aerobic zone was 135-165
anaerobic zone was 165-180
red line zone was 180-190
So I have set my HRM zone to 135-165.
Dutchie