I had two training runs this week. One was 45 minutes and it was 15 min easy / 15 min threshold / 15 min easy. The second was 90 minutes easy. My pace for them was 9:00 / 7:00 / 9:00 and 8:35 for the second overall.
When running the first run my heart rate never got over 160, which seemed odd to me and I think was a misread by my watch. When I ran the exact same route 2 days later for my 90 minute run I was 167 average and got all the way up to 185 (my max is 190).
I use the wrist based heart rate, which I know is not very reliable, and so I'm pretty certain that this is all just the watch doing a so-so job. Still, I'm wondering from any more experienced runners out there if is some explanation based on the variable of distance/pace/etc... that makes this make sense? Does running slower at a longer distance possibly result in a higher average HR than doing a 15/15/15 with a threshold run in there? To say it another way, can I achieve a higher HR in the midst of a long easy run than I can in a short fast section of a run? That doesn't seem right to me, but I'm pretty new to both running and monitoring HR stuff.
PS - both runs were in the same area, so elevation/altitude/the hills wouldn't have made a difference.
