I've been into the running scene too; but to no great success; I read Dean Karnazas' book pictured.
Even Karnazas, when he started out, ran some great distance and said he was wore out to the point of a lot of bed time for 2 weeks. I can relate to that, some of that can really wear you out, the older the worse but it's not just that, you've got to do your protein and so on. Maybe electrolyte drinks as well.
Still, a pretty good book, even to the casual reader, heck, he even passed out on some city street or just off it, I forget, in one of his ultra-marathons.
Now, there is the cross-training phenomenon and now there is the "Tough Mudder" race. Those tax your body to the max like the ultra-marathons. Sort of on the same note, I enjoy that American Ninja show but I don't think it's as intensive as the above.
Real runners allegedly at forums like
"Let's Run" don't really consider what Karnazes is doing as that great.
I got into it for awhile, read up on Prefontaine, fascinating person.