How important is the 10 beat range for your lower limit? In Maffetone's article he doesn't mention it at all.
Nicole's reply:
Hi, the thing to remember is that once you have worked out your max MAF heart rate, the plan is not to exceed that number during your MAF training. It would be impossible to run/walk your whole training session sticking to one number so that is where the 10 beat range comes into play. Some people in fact choose to go more than 10 beasts below their max MAF heart rate so in essence the 10 beats is just a guide.
You might find this article useful where Phil Maffetone does talk about the 10 beat range. Want speed? Slow down!