Not sure if this ever happended to anyone, but back in the day, during a championship high-school 800M final, I found myself trying to squeeze my butt cheeks together to prevent a turd from weighing down my shorts, with 250M to go. It was a struggle like no other, and I could either poop my pants and medal, or save the turd for later and place somewhere back in the 7th or 8th (last). Sure enough I saved the embarrassment and finished last - not sure if my team-mates actually ever bought my excuse!