A question on involuntary defecation (TMI)

A friend of mine recently had a mountain biking accident where he was attempting to do a “manual” (a wheelie without pedalling) and overbalanced so he fell on his back. He didn’t fall hard and only has minor injuries, but he tells me, with some embarrassment, that as he hit the ground a small amount of faeces was expelled from his rear. He had recently evacuated his bowels voluntarily so there won’t have been a whole lot in there, though enough to cut the ride short.

Question is, what is the most likely mechanism that caused this? He’s not been in the habit of shitting his pants when he’s had other more serious accidents so we don’t think it was a “fear poo”. All we can think is that maybe the sphincter was relaxed at the exact moment of impact and, like an open tube of toothpaste hit with a mallet, the body was squeezed briefly and the faecal matter took the path of least resistance.

Any insights?

How recently had he gone voluntarily, before this incident occurred? Is it possible there could have been something that didn’t quite make it out the first time, but was right there waiting when the impact occurred?

Earlier that morning, 2 - 3 hours prior to the event.

Does he take Flo-Max, or the generic Tamsulosin? They relax the sphincter.

I will ask…

No, he does not. He doesn’t take any medication at all.


If he landed on his back, the poo was moving downward. His body stopped, but the poo kept moving down.
Maybe the force moving the poo was stronger than the sphincter that tried to stop it.

And: Trying to second-guess “When will my body invoke ‘fight or flight’?” is not really a fool-proof way of approaching the situation.

Wouldn’t that be more applicable if he landed on his bum with his spine vertical?

Did he land on his lower back? The impact may have been hard enough to shock the nerves that control the rectum and anus, leading to a brief spasm and the observed defecation.

Although it’s considered poor form to cite Bill Cosby these days, he did cover this in his standup routine, decades ago (emphasis added.)

You do know you’re not fooling anyone :wink:

The only time it happened to me was in Bolivia,when I was afflicted by some kind of intestinal disorder, which left me ambulatory and with seemingly relatively normal bowels, but feeling discomfiture… I went to take a piss, and when I released, I shit my pants. Much to my surprise, as it wasn’t even diarrhea. So I suppose, under conditions that are outside the ordinary, body parts can function with a mind of their own.