Dilemma which occurs when you need to shit but are far away from the nearest toilet. Running will get you there faster but the natural laxative qualities of running will make you want to shit more. Walking doesn't make you want to shit nearly as much but it takes you twice as long to get to the toilet. Hence, you are caught in a Catch 20-Poo.
"I went jogging the other day and about a half mile from home I got caught in a Catch 20-Poo".