IOWA CITY, Iowa -- Some runners experience cramps and diarrhea while running, suggesting that colonic activity increases during exercise. However, a recently published University of Iowa Health Care study suggests that for people with less athletic training, progressive exercise like running or bicycling may instead decrease the normal number of propelling and non-propelling contractions in the colon. Following exercise, a large number of forward-propelling contractions return, which may facilitate normal defecation.
"We wanted to better understand how the colon normally functions," said Satish S. C. Rao, M.D., Ph.D, UI associate professor of internal medicine and lead investigator. "We expected to see an increase in colonic activity during exercise, but we found instead that colonic activity changes significantly in surprising ways."
UI researchers in gastroenterology and exercise science used advanced technology to study the colonic activity of 11 healthy non-athletes, six men and five women, ages 23 to 55. The participants exercised on stationary bikes at three different levels of aerobic capacity for 15 minute-periods each, followed by 15 minutes of rest. A slim, solid-state probe placed in the colon measured muscle activity before, during and after each exercise period.
The researchers found that as the subjects' exercise level increased from 25 to 50 to 75 percent of maximum aerobic capacity, the muscles that propel material in the colon forward or backward or break it down decreased their activity. This finding about non-athletes was contrary to some previous colon and exercise studies that focused on athletes. The UI researchers also found that within 30 minutes following exercise the colon resumes its forward propelling motion, allowing it to empty better.
Rao said the decrease in colonic activity during exercise may be caused by "competition."