Background: Occult (i.e., non-visible) gastrointestinal (GI) bleeding is a well-recognized complication that can occur during vigorous endurance physical exertion, especially in the heat. Objectives: The purpose of this study was to investigate the incidence of GI bleeding during a non-impact (cycling) prolonged race (161-km) in the heat. Methods: Twenty-five experienced cyclists (21 males and 4 females, 49 ± 9 y, 83.7 ± 14.8 kg) were completed a summer 161-km cycling event. Following the race, participants were given a fecal occult blood test and were instructed to retrieve their first bowel movement. Results: Mean race dry air and wet bulb globe temperature (WBGT) were 36.0 ± 5.2°C, and 31.8 ± 3.6°C, respectively. Of the 25 subjects, two (8%) produced positive results for fecal occult blood while an additional two (16%) experienced constipation, hard stools, diarrhea or vomiting. Conclusions: These data showed a low incidence of GI complaints and occult bleeding during a prolonged cycling event in the heat, indicating the low-impact exercise such as cycling may lessen some of the occult GI bleeding previously reported in distance running in the heat.
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