Gastroenterologists tell The Healthy that exercise stimulates hormones in your body. In particular, the vasoactive intestinal peptide stimulates movement in your gut. Adrenaline and the peptide hormone gastrin also get things going in your digestive system. If you’re doing a race, your nerves could also give these hormones a boost.
Exercise also shifts your blood from the digestive tract to your muscles, causing your bowels to contract. Sometimes, drinking too much fluid with electrolytes can cause your bowels to loosen. Sports drinks with a carb solution of more than 7% can result in GI distress, according to the International Foundation for Gastrointestinal Disorders.
Certain foods might awaken your bowels during exercise. Natural and artificial sweeteners, fats, grains, dairy, and caffeine could be the culprits of your mid-workout urge to poop, according to Unity Point Health. Short, intense runs might not present too much of a problem, but longer runs at a moderate pace could necessitate your need to go.