I think he's wrong about running at 5:20 pace with 155 bpm. That is absoluptely impossible, the lowest that easy pace can go is 5:33 on the VDOT table (85) which would make him a 3:39 miler as a triathlete. He still kind of has the right concept on base work. I put this just in case anyone was curious about base work which I've mentioned several times. The best indicator for easy pace is if you can breathe comfortably at a 3-3 breathing rhythm (3 steps on inhale, 3 steps on exhale). If it's forced, it will feel like suffocating because the heart is beating too fast and signaling the lungs to take in more oxygen, therefore the runner starts to go into a 2-2 rhythm.