My forerunner 945 is showing very high heart rates even on a pace and feel that's too easy for me. I did a half marathon run and probably around 8kms the heart rate pushed past threshold category and too high. I did 22 Kms and feel fine and didn't push myself too much. I have had heart belts before and also faced very high heart levels.....how am I supposed to run slower then what I feel is already too slow and get to low aerobic use. As you can see by the images below my heart rate was in excess of 180 for most of the run. How does that make any sense