Emergency pit stops are a common problem for runners on their way to the finish line—and, indeed, sometimes there’s no time to get to the port-a-potty. One survey of marathoners in the U.K. found that the vast majority (83 percent) frequently suffered at least one gastrointestinal disturbance during or right after a long run. The issues were more likely to affect women than men, with 74 percent of women reporting the urge to have a bowel movement and 68 percent getting diarrhea. Hence the term “runners’ trots.” Symptoms are nearly twice as likely to happen while running than other high-endurance sports like cycling and swimming, which suggests that the jostling of the intestines plays a role. At the same time, while running long distances, blood flow is diverted from the intestines to the muscles at work.
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