High HR wrote:
I think, as you said, I'm simply not fit enough to have an "easy" run yet. I've been on ~20mpw for a while so I need to up my mileage. The last time I had to build a proper base was probably 15 years ago in high school and HRMs weren't exactly widespread then. So I have no idea what my heart was or wasn't doing at the time, just the pace we were running (which I'm not comparing my current pace to, of course).
I'll gradually increase mileage until I hit around 35mpw and hold it there for a little bit, checking my HR every few weeks to see if it comes down. If it's any indication, my resting HR has come down a few BPM over the last few months.
This should work for you. Let me make a couple of guesses and add this.
If... IF... your goal is to get faster over the 5k, and NOT to train for a marathon, you could try continuing to do the "faster" 9-10 minute pace for easy runs and just take walk breaks when your HR exceeds some predetermined "easy" level for more than a few seconds. Walk until your HR drops a predetermined level below that mark and then resume running. Let me pick a number (not necessarily what you would choose) to illustrate.
Assume you set your max "easy" HR at 150. When you hit, say 151-152, stop running and walk until it drops to 145 and then resume running. Of course, the first time you do this, your walking intervals will get a bit longer the farther you run. But over time, you'll be able to run a little longer before you have to take a walking break.
The downside of Maffetone and similar super slow pace training is that the slow pace isn't remotely close to your race pace and thus your easy pace form isn't remotely similar to your race pace. It's more of a shuffle. Sure, your heart is getting a recovery workout at this super slow pace, but your form is devolving into a shuffle.
The benefit of my suggested run/walk approach is that your easy pace is fast enough to not be a shuffle. It's a little closer to how your legs must move at 5k race pace. You can also do this on tempo runs. I use a 5min/1min ratio so my running pace (during the running portion) on four mile tempos is closer to my 5k race pace.
Disclaimer: I'm not too familiar with the Maffetone method. Perhaps there's an option to do what I'm suggesting.