In any compromise we lose certain options, and for most of us, we lose the option of real endurance training and development. I came into running during the peak of the U. S. running boom, and it was neat to see so many people running and running so well. His philosophy was less is more at least if it is always hard. And this was before heart rate monitors and the MYTH of altitude training. They RAN, they ran a lot, and they ran often pretty darn hard.
Volume builds fundamental endurance.
The Japanese and Chinese marathoners are regularly running 130 miles a week or more, and our best recent U. S. marathoner left the U. S. to train with a stable of Japanese runners to find others motivated enough to challenge his needs. The Kenyans are running 3 times a day and mileage levels that clearly exceed 100 miles a week, and those are often quality distance sessions too. Read train hard, win easy that describes what goes on in those Kenyan camps. We need to do solid long tempo runs. We need to do elemental speed training which is what Tuesdays and Thursdays is all about.