Asking for a friend

At some point, fighting to achieve a weekly mileage goal becomes counter-productive. My "friend" wants to know where that point is.

My friend tries for 80 miles (used to be 70) per week. He doesn't always make it, but he usually does, and this is partly due to his GVRAT experience. Since he ran all those miles for GVRAT, he now doesn't want to back off. He's worried that that would negatively impact his fitness. Of course, running too many miles can lead to injury, which would also negatively impact fitness.

But the real problem (and the reason for the question) is that he does some strange things to achieve these miles. Like run VERY slowly. Like running on the mill. Etc. What a nutcase.