CONTACT: BECKY SOGLIN
2130 Medical Laboratories
Iowa City IA 52242
(319) 335-6660; fax (319) 335-8034
Release: Aug. 18, 1999
UI researchers learn more about how exercise affects
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
"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
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
"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