I can't run on a full bladder. In fact, I can't run with anything in my bladder. If I drink coffee or any other drink an hour before I run, I am constantly stopping and starting my treadmill, taking potty breaks. To me, there's nothing worse than that, so I get in this rush to run almost immediately after I finish a drink of some sort in the morning.
This has nothing to do with ability, just everything to do with discomfort and annoyance. I think this is why I would never do well in a race. O crud, there's the finish line. Well, those guys are going to beat me cause I gotta go to the bathroom! I would be making full use of those port-a-potties, believe me.
Everywhere I go I have to plot my mental map to the bathroom. This makes the poor Professor's life only slightly miserable.