In a lightly wooded area next to a running path. In a stranger’s bathroom. One hundred meters from the finish line.

These are just a few of the places runners we talked to have admitted to, well, crapping out, during a run. And we don’t mean figuratively: Yep, we’re talking about poop.

Harrison Glotman, 25, a 2014 New York City Marathon finisher, was training in an unfamiliar neightborhood when he realized he had to go, stat. Realizing his options were either drop a deuce on a residential lawn or go door-to-door and ask strangers to have mercy on his bowels, Glotman chose the latter. Luckily, the owner of the first house he tried took puty on him and offered him his bathroom.

Not all stories end with a flush, though. Kyle Simmons, 27, a 100-mile ultra marathoner, learned this the hard way at the Krispy Kreme Challenge, North Carolina’s premiere doughnut-eating race (yes, you read that right). After accidentally fertilizing his pants, he withdrew from the course in shame.

The Science Behind Our Bathroom Behavior

Yeah, it’s an awkward topic. (Go ahead and get out your giggles.) But anyone who runs or exercises regularly knows that unpredictable bowel movements are just part of the sport. They can come quickly and without warning, slowly and painfully, or sometimes not at all.

So what’s really going on? Put simply, working out increases movement in your gastrointestinal tract, says Jeff Crespin M.D., a gasteroenterologist. “When you exercise, there’s more stimulation, which increases upper gastric motility,” Crespin says. “This carries over to the lower gastrointestinal (GI) tract.” Translation: The more you moved, the more you poop.