The Athlete and the GI Tract

by R. Rafoth MD
Sun Mountain Lodge - 1/2004

Exercise Related Gastrointestinal Symptoms

Gastrointestinal symptoms are common in athletes - in triathletes they are more common than musculoskeletal complaints and injuries. They are more common in high intensity situations (performing at >70% VO2max), but can also be a problem with less intense exercise in those who are out of shape as well as in endurance events. What are the most common GI symptoms? The following symptoms are reported by >50% of regular athletes during heavy exercise (both in training and competitive events).

With running, lower GI symptoms (cramps, diarrhea, and rectal urgency) are more common than upper (nausea), with rectal urgency being the most common symptom in up to 63% of regular runners followed by diarrhea in 54%.

Modifiers of GI Symptoms

These symptoms are modified in both severity and frequency by:
  1. The presence of symptoms in the non exercise period - if the athlete has irritable bowel syndrome before they begin to exercise regularly, they will probably have more symptoms afterwards.
  2. Age
  3. Gender
  4. Diet - this is important because of the many, varied approaches (eating and supplements) used by athletes to give them "that extra edge".
  5. Training Status Less trained individuals have more symptoms. The gut does not adapting with the stress of progressive training. But, training will help prevent GI symptoms. An example of indirect adaptation. May be tied into the next one:
  6. Intensity of exercise(3 of 5 studies showed a correlation). Especially in runners, symptoms seem most likely to occur after an episode of particularly severe exertion OR during a period of rapid increase in training mileage.
  7. Mode of exercise
  8. Duration of exercise - symptoms are more common the longer the event (marathon for example)
  9. Hydration status

    80% of marathoners with a 4% weight loss have GI symptoms

    Controlled dehydration in a sauna with a set exercise regimen - with dehydration significant slowing of gastric emptying and increase in nausea for a set amount of exercise.

  10. Certain non dietary supplements/meds

    Next we'll talk about the most common exercise related GI system disorders.