I have a Polar HRM but all my runs seem to be between 160 - 170 and today was 180+...seems higher in the morning and thought that might be as I usually train at night...and always at 6mph whatever the rate!!! I have had a couple of long runs at 155ish but that's really unusual. Should I do a bit of interval/ lampost running? or maybe a bit of hills? there's a nice 100m hill quite near which might be useful.