Just to be a little more specific: Here's Maffetone's formula as described on his website, a website hyperlinked from Leitner's FAQ:
"The 180 Formula
To find your maximum aerobic heart rate:
Subtract your age from 180 (180 - age).
Modify this number by selecting one of the following categories:
If you have or are recovering from a major illness (heart disease, any operation, any hospital stay) or on any regular medication, subtract 10.
If you have not exercised before, you have exercised but have been injured or are regressing in your running, or you often get colds or flu or have allergies, subtract 5.
If you have been exercising for up to two years with no real problems and have not had colds or flu more than once or twice a year, subtract 0.
If you have been exercising for more than two years without any problems, making progress in competition without injury, add 5.
For example, if you are 30 years old and fit into category b: 180 - 30 = 150, and 150 - 5 = 145. This is your maximum aerobic heart rate. For efficient base building, you should train at or below this level throughout your base period."
Using me as an example: I'm 48 and fit. 180 minus 48 + 5 = 137. That's my Maffetone or "Maff" heart rate. Maffetone claims that ALL of my running during my base phase should be at this HR or below.
The Maff formula cares nothing for actual max HR, which is to say nothing for percentages of max HR or HR reserve. But since my actual max HR happens to be 196, my Maff HR is exactly 70% of max.
Maff's formula stipulates, in other words, that all my training runs, including long runs, should be at 70% of HR max or below. All.
Leitner trained this way and lowered his 50 mile time by more than two hours. He ran a BQ (3:17, as I recall) untapered, at the end of a 70 mile week, with a surprisingly low HR. He seems to have turned himself into a quite remarkable aerobic engine, of a kind.
It's not clear how applicable this sort of training is to elite runners, needless to say. My own hunch is that this is an exceptionally good way for a relatively untrained runner, of ANY talent level, to spend the first several years of his or her career.
I was curious, in any case, to hear Renato's opinion. Curious about yours, too.