Not sure if I've mentioned this before, but I began having all sorts of health-related issues a few years ago—heart palpitations, constant colds and flus, etc.
Then a cardiologist diagnosed me with a heart block and some scarring on my heart ("very common" he said with distance runners my age)
Somebody mentioned 'overtraining' to me, and recommended the MAF (
https://philmaffetone.com/method/) method. At my wit's end, I bought in completely.
The TL;DR version is this: Max Heartrate is, at best, an arbitrary number, and that many of us train way too hard for way too long, which leads to increased fat and other issues.
My MAF method to begin was 130—don't let your heart go above that number.
At first, even a brisk jog would have me in the 160's, which meant that I basically shuffeled for a few minutes and then had to walk.
A couple of years later, following this method religiously, I can run an 8-minute mile without my heartrate going over 130. My walking heartrate is 20bpm lower than it was at the beginning, and my HR recovery is at least triple what it was.
The best part? I run less, I walk more, and I am around 9or 10% bodyfat year round. I feel good, and haven't had a cold in two years. It's almost like I went back to my mid-20's.
I guess the takeaway here is don't work-out harder, work-out smarter.
Anyone struggling with constant plateaus, I'd recommend giving this method a try.