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."
"Blood is stolen away from the gut to other muscles during a workout," he explained, "so if there's less blood flowing to the gut, the gut muscles must shut down activity."
He also said the findings show that it's not necessarily true that "better" colonic function means more colonic activity. Part of the colon's job is also to slow down activity at certain times, he said.
Rao said the UI study was unique in how it combined a focus on untrained people (rather than athletes), examination of at least 75 percent of the colon (compared to 25 percent in studies using older technology) and a single session of graded exercise.
The study also differed from other investigations in that the colonic probe, which causes no discomfort, was placed in the participants the day before the exercise tests, allowing their colons to return to a normal state. Thus, the participants' colons were not cleaned out. Previous studies looked at subjects whose colons were emptied by enema treatment or lavage immediately before testing.
"The colon normally has stool in it, so the question was how do you study an organ that has some material inside it?" Rao said. "Using x-ray imaging to study the colon is not possible because the colon works slowly and would require an unsafe level of radiation to track all the changes.
"New technology developed over the last 10 years allows us to visualize the entire colon from the inside, even in the presence of material. People can then go about their normal activities while we measure the colonic activity," he added.
Rao said learning more about colonic muscles may help researchers investigate common colon problems such as constipation, diverticular disease, colon cancer and inflammatory conditions such as colitis.
"One implication of the study is that regular physical exercise may benefit people in terms of normal colonic activity," Rao said. "By extension, this may help decrease a person's chances of colon cancer."
Before beginning any new exercise program, people should consult a physician.
The study was funded by an American Gastroenterology Association - Smith Kline French Beecham Clinical Research Award and a General Clinical Research Center Grant from the National Institutes of Health. The findings were published in the May issue of the American Journal of Physiology. The study was part of a larger study on colonic function under physiological conditions.