Effect of heavy exercise on gastrointestinal transit in endurance athletes

Background and aims. Disturbances in transit of the gastrointestinal (GI) tract have been proposed to be involved in the etiology of the GI symptoms in heavy exercise. However, the results are conflicting. In the present study, we investigated the effect of heavy exercise on GI transit in well-trained athletes. Methods. Fifteen healthy well-trained athletes underwent measurement of gastric emptying, small bowel transit and colonic transit with radiopaque markers during a resting week and during a week with heavy training. GI symptoms, bowel habits, food intake and exercise performed were registered. Results. Small bowel transit was accelerated during the training period compared with the resting period (3.7 (2.6--12.3) h vs. 6.9 (4.2--17.2) h, p == 0.04). Segmental colonic transit in the descending colon was significantly accelerated during exercise compared with rest (0.1 (0--0.4) h vs. 0.4 (0.1--0.7) h, p == 0.03). Gastric emptying did not change during exercise compared with resting (2.4 (0.7--4.6) h vs. 1.8 (0.9--3.3) h, p == 0.16). Stool frequency increased significantly during the week with heavy exercise compared with the week without training (1.5 (1.2--1.8) stools/day vs. 1.3 (1.0--1.7) stools/day, p == 0.02). Stool consistency according to Bristol Stool Form Scale tended to be looser during the training period compared with the resting period (4.2 (3.7--4.5) vs. 3.9 (3.0--4.3), p == 0.08). Conclusion. Heavy exercise affects transit in the GI tract, which might be involved in the generation of GI symptoms and altered stool frequency/consistency in endurance athletes.