Well here is something to read.
Old Mike
Gastrointestinal Physiology During Exercise
www.cptips.com/smexphy.htm4) The Colon (ascending, transverse, descending, sigmoid, and rectum)
As opposed to the small intestine, the effects of exercise on the colon are marked and the results (diarrhea, urgency, and incontinence) readily evident. •There is a change in motility. There are two types of motility in the colon - segmenting activity and propulsive waves. As elsewhere in the GI system, there is a decrease in segmenting contractions (which usually act to delay transit through the colon) and propulsive or phasic waves are then unopposed. The result is a decrease in oral - rectal transit time. ◦mechanical effects, especially with the jostling of running, may contribute to the more rapid movement of fecal material down the descending colon with the result being rectal urgency - which is most common in running events and directly correlates with the duration of the running event.
•There is a change in colonic mucosal integrity with exercise. It is unclear whether this is related to mechanical effects on an organ which has a long mesentery or is a result of mucosal damage from a decrease in visceral blood flow. Evidence includes: ◦an increase in endotoxemia (measured in blood samples) ◾there is a significant correlation between endotoxin levels and symptoms of nausea, vomiting, and diarrhea,
◦colonoscopic evidence of ischemic colitis picture (confirmed by biopsy)
◦an increase in occult GI blood loss that directly correlates with exercise duration