in the springfield 5k, if all entered and worthless side charcters like a sherpa arent included, my top ten would be:
1. 18:30 Smithers (pedaled a bike while having reaction to bee sting, he has some toughness)
2. 18:53 Groundskeeper Willy (one of the only athletic looking guys)
3. 19:14 Skinner (his army days)
4. 19:27 Cletus (runners body at least)
5. 19:49 Carl (can play basketball, so he is somewhat athletic)
6: 20:24 Ned Flanders (the shoes; he stays in good shape)
7. 20:44.2 Snake (running from the cops is some practice)
8. 20:44.7 Lou the cop (seemed the most fit of the cops)
9. 21:34 Marge (she showed something in her cop days)
10. 22:00 Herman the one armed military guy (had to do some running back in the day)
conclusion, the simpsons dont have many athletic main characters. in fact i think i overestimated their ability