Notes
New approach: I tried very hard not to go over 153 heartbeats a minute (except the last 100 yards). During the whole run I was 50 minutes and 56 seconds within my zone: 140 - 160 bpm. It felt good but sometimes was difficult to keep it since I had to slow down to a 10 minutes/mile speed. And around 4 miles I got tired but not really from running but from trying not to run too fast. But it's worth the tryouts.