I've tried MAF with no real success. I've tried to keep my heart rate down and just run really easy. That is fine, but I don't feel like it is getting me any faster. I decided today that I am going back to the run/walk intervals and quit worrying about my heart rate. I stayed relatively injury free doing that and could see progress. Did 5/1 intervals today for five miles and it was the best run I've had in a long, long time. I think that little one minute walk break really helps me.
That is a happy faced runner. My average heart rate was 152 with a max of 179, but I was pushing it at the end.