I am 41 and have started running from august. I have noticed my slow runs increase my heart rate more than the faster runs. My runs with a pace of 9 mins/km hits an average heart rate of 156. I have noticed whenever I reduce my speed my heart rate goes up mostly hitting max heart rate zone.
When I do 7 mins/km , I hit an average heart rate of 147. Much better than slower runs!
Why is that my body is working at a high heart rate for slower, easier runs?
Note that even though the heart rate is high I am not feeling like straining as I do with faster runs when I run slow.