I would definetely write stress diarrhoea. I did some researches on the web and I didn't find other solutions. The "psychological rather than physical sense" you mentioned is a good point, but as a matter of fact, we're talking about dogs... not men & women. In http://www.beaglesunlimited.com/beaglehealth_canineperforman... we read:


The timing of food administration also is important. Dogs that work hard with food in the gastrointestinal tract may experience impaired performance and gastrointestinal upset. Because the gastrointestinal tract and the muscular system both require a large blood supply while working, neither can function optimally if both try to work intensely at the same time.

Exercise often is associated with loose and even bloody stools. This condition often referred to as “stress diarrhea,” may be due to exercising while the gastrointestinal tract is processing a large meal. Stress diarrhea can often be improved or prevented if the dog has time to completely process a meal and defecate its remains before his next bout of exercise

Nothing to do with the "dog's psychological life" as you can see.