The review of 8 studies on gastrointestinal injury related to exercise found that distress set in after the 2-hour mark, which is significant because no one has ever completed the 26.2-mile marathon in that time.
Running can be good for your health, but apparently running a marathon—which no one has ever done in under 2 hours—is likely to bring on gastrointestinal (GI) distress.
A review of studies on the effect of acute exercise on GI injury finds that exercising more than 2 hours at more than 60% of a person’s maximum intensity level can bring on symptoms of gastrointestinal distress, “irrespective of fitness status.” This is especially true in the heat. Those with a predisposition to GI problems are more likely to have problems related to strenuous exercise, according to the review, which appeared this month in Alimentary Pharmacology & Therapeutics.
“While there is evidence for health benefits of moderate exercise in patients with inflammatory bowel disease or functional gastrointestinal disorders, the safety of more strenuous exercise has not been established,” the researchers wrote.
The researchers reviewed 8 previous studies to draw their conclusions. The condition they identified has been labeled “exercise-induced gastrointestinal syndrome.”
GI problems are common among marathoners, even though many athletes do not want to discuss them. One study found up to 71% of long distance runners experience cramping or diarrhea, for physiological reasons that include the diversion of blood flow to the muscles to severe jostling of the intestines. Nerves may play a part as well.
Identification of 2 hours as the threshold when GI problems start to set in during intense exercise is significant, since no runner has ever broken the 2-hour barrier for the 26.2-mile race. The recognized world record is 2:02:57, set in 2014, and the average finishing time for men in the United States is about 4 hours, 20 minutes.
“Exercise-induced gastrointestinal syndrome has the ability to create acute disturbances in the health of the gastrointestinal tract due to multiple physiological changes association with hypofusion and ischemia, epithelial injury, impaired barrier function, impaired nutrient absorption, altered gastric and intestinal mobility, endotoxemia, [and] local and systemic inflammation,” the authors state. “Whether the syndrome is associated with the development of chronic disease acutely or after repeated insults remains unclear, but is of concern and requires more research.”
Costa RJS, Snipe RMJ, Kitic CM, Gibson PR. Systematic review: exercise-induced gastrointestinal syndrome—implications for health and intestinal disease [published online June 7, 2017]. Aliment Pharmacol Ther. 2017; doi: 10.1111/apt.14157.