A few people have asked me when I'm going to stop the Hadd experiment and "do some real training". If I were a marathoner, I'd probably do Hadd-training forever. I believe it's possible to run a good marathon (even a PB), just off Hadd, and nothing else.
Hadd-training is a method of developing 'base' by using heart-rate to guide effort during a particular training run. Base was made famous by Arthur Lydiard, who had all his runners, from 800m specialists to marathoners, running 100 mile weeks during the base phase. The Lydiard method of training is often thought to mean lots of slow running. It's actually base training (aerobic running), followed by 4 weeks of hill training, 4 weeks of anaerobic (intervals) training, then speedwork (sprinting), tapering and racing.
I'm putting off doing any "real training" because I want to race a couple of 3000 metre events just off Hadd-training. I'm curious to see what simple aerobic conditioning will produce in the way of a 3000 metre time. After that, I may do some anaerobic running and speedwork. Or I may not. I'm actually enjoying the less frenetic and more contemplative aspects of aerobic running. I've also been able to run a lot, without becoming injured. I like running.