The concept of running MAF is a valid one. I think there are much better ways of training though.

I ran MAF when I started running again last year. Helped me build my mileage up to 60 per week.

MAF is actually zone 3 for me. I run my easy miles under MAF and try to stay a couple beats under going aerobic.

I still do a tempo once a week and either intervals at critical velocity one day or mix in faster miles on my long run.

I generally find this much more effective than MAF and I’m not beating my body up.

During the coldest and warmest 2-3 months of the year I generally run mostly zone 2 and don’t worry about intervals or tempo.

I’m a big fan of MAF training for building mileage.

I think your HR does limit the damage you do. Some days it is really hard to be at the top end of your MAF zone.

I combine it with Barry P training.

I will also say I found MAF very hard on the bike. I needed to start out by incorporating it as intervals. I’m pretty strong on the bike and even today a 2 Hr. MAF ride is a solid workout. Whereas a 2 Hr. MAF run is easy.

Back to running and MAF. I would be at the top end when feeling good. For shorter recovery runs I’m at the bottom end. I don’t spike above. For long runs I start out at the bottom end for first third then middle for middle third and top end for the final third. So, basically build within the run, which allows me to hold my pace pretty consistent throughout and when in good shape, negative split the long run.

If it helps I’m 43, 80 kg’s and a sub 3 hr marathoner off of MAF, Barry P and a bit of Phitzinger.

You definitely can overtrain on MAF.

MAF is using a formula for getting your heart rate which is just plain wrong. The formula is a straight line on a graph with millions of dots and huge deviation.
Formulas are correct for the average population not for the individual.

For me for example my MAF heart rate would be waaay to high for easy running since my max heart rate is comparably low and I'd be overcooked and injured within weeks.

Do a test what's your max HR or take it from a 5k run with a sprint finish and run at 75% of max hr or lower.

Also listen to Dr. Stephen Seiler on what is easy running (spoiler: it pretty much boils down to the above)

It's 2020 and HR formulas should finally die. It's known forever that they can and will be extremely off for the individual.

"I don't use the 180 formula for any of the athletes I coach" - Phil Maffetone

It's a starting point when you have no other information.

as a side note... from a guy in the 55-59 AG.

It's not the "heart energy" expended that those above 75% runs do to me, it is the possibility of injury.

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http://www.fitspeek.com the Fraser Valley's fitness, wellness, and endurance sports podcast

My view is that there is no Maffetone method as such. He didn’t invent the long and slow aerobic running, it had existed long before. What he introduced is the mostly useless simplistic formula and hoopla/religion around it.
I believe there is much more value in just several pages of Barry P posts which can be found on this forum.

Dimm