depends on the game shape he have before, but in the normal range a gs down is likely with 90 minutes.
I think more often than not, this is the case...but i had a weird thing happen this past week...One of my players had 90 minutes last week, and his DMI almost doubled, and his game shape went from 7 to 8. I was not expecting that at all, in fact I was bracing for him to drop to 6. Total fluke, but wheww!! :-) I'll take it! (By the way, I did NOT train Game Shape)