Runner’s diarrhoea

Runner’s diarrhoea, sometimes called runner’s diarrhea, refers to loose stools or an urgent need to open the bowels during or after running. This digestive disorder is relatively common among endurance athletes, particularly during long runs, marathons or competitions.

Although often benign, runner’s diarrhoea can disrupt training and performance. It is generally related to a combination of mechanical, digestive and nutritional factors associated with exercise, and corresponds to accelerated intestinal transit during or immediately after exercise.

The digestive tract is particularly sensitive to the physiological consequences of exercise. Running generates repeated impacts that cause micro-jolts in the digestive organs; these vibrations can stimulate intestinal transit and promote diarrhoea.

During exercise, a large proportion of blood flow is also redirected to the working muscles, at the expense of the digestive system. This reduction in intestinal perfusion can disrupt the normal functioning of the digestive tract. Similarly, activation of the sympathetic nervous system during competition or intense sessions can speed up intestinal transit.

Digestive disorders are relatively common in endurance sports, particularly over long distances. Runner’s diarrhoea is therefore particularly associated with long runs, marathons and trail running.

Exercise-related factors

Some foods consumed before exercise can irritate the bowel and promote digestive disorders, as can competition stress, which speeds up transit via the sympathetic nervous system.

Dietary and contextual factors

Several factors can increase the risk of digestive disorders during running: a meal too close to training, high-fibre foods, fatty or spicy foods, coffee or energy drinks, excessive hydration, or competition stress. Long distances such as the marathon or trail running are particularly associated with these disorders.

Runner’s diarrhoea presents with loose stools, an urgent need to go to the toilet, abdominal cramps and bowel rumbling, most often during prolonged exercise such as long runs or endurance competitions. It may be accompanied by bloating, a feeling of digestive urgency, nausea or intestinal discomfort. In most cases, symptoms disappear quickly once exercise stops.

When to see a doctor?

A medical consultation is recommended if the diarrhoea persists for several days, if it is associated with blood in the stools, if significant abdominal pain appears, or if episodes are very frequent during training. A doctor can look for a food intolerance, a digestive infection or an intestinal disease.

Prevention relies above all on a good nutrition strategy: opt for a light, easily digestible meal, allow 2 to 3 hours between the meal and exercise, and systematically test any new eating habit in training before using it in competition. Managing competition stress also helps limit the risk of digestive disorders.