• gastrointestinal flow;
  • exercise;
  • gastric emptying;
  • gastric motility;
  • gastroenteropancreatic hormone

Different types of upper and lower gastrointestinal (GI) symptoms occur in 30–50% of participants in endurance exercise. These symptoms may be related to more than one causal factor. When exercise is extremely intense or when dehydration causes hypovolemia, exercise induces changes in GI blood flow that may lead to local hypoxia of the GI tract and increased neural activity of the plexus submucosa of the gut. As a result, secretion of some gastroenteropancreatic hormones may be enhanced, and decreased absorption parallel with increased secretion may take place. Diarrhea, intestinal cramping, delayed gastric emptying and bleeding of the serosa of the stomach and colon may result. This bleeding may be aggravated by the use of anti-inflammatory drugs. Exercise reduces GI tone and motility, and tends to delay transit. A reduction in tone may lead to reflux from the stomach or loose stools escaping from the colon. Gastric emptying is not influenced at moderate exercise intensities, but will be inhibited at maximal exercise intensities or during a state of dehydration. The latter likely induces a cascade of changes in hormone secretion and nervous output, leading to a change in absorption, secretion and gut motility. Additionally, severe emotional or mental strain may further influence GI functioning.