Stomach problems when running: Where they come from and what to avoid

Intensity and digestion in a dilemma: When all systems in the body are occupied by a physical challenge, the stomach gets a raw deal, which often results in digestive problems. Intensive endurance sports and digestion are two activities that limit each other.

Practically everyone who loves longer physical challenges has some experience with digestive problems. The reason is obvious: Intensive physical activity uses the available oxygen primarily for the supply of energy in the muscles, the other systems, such as digestion, are reduced to a minimum. The microclimate of the stomach is often disrupted by physical exertion.

Depending on the location, a distinction is made between problems of the upper and lower digestive tract. Symptoms of the upper digestive tract include burping, heartburn, chest pain, nausea and vomiting. In endurance sports, stomach problems occur mainly in running, cycling and triathlon. The more intense an exercise load is and the longer it lasts, the more frequent are digestive problems. In a 10 km run or a hike, far less than in a marathon or Ironman, for example.

Heartburn and its causes
Heartburn can occur due to increased acid production in the stomach or due to so-called stomach ulcers. Triggering factors can be the regular intake of certain medications such as anti-inflammatory drugs or cortisone. Nicotine, caffeine and alcohol as well as frequent large amounts of protein-rich food can additionally cause these disorders. Heartburn is not caused by physical activity, but by a disorder of the closing mechanism between the esophagus and the stomach. Nevertheless, an increased transfer of gastric acid to the oesophagus could also be detected in healthy probands during running. The shocks associated with running are probably responsible for this, because the stomach’s ability to absorb food deteriorates massively as a result of the constant impacts. This phenomenon is much less pronounced when cycling.

If the food is eaten shortly before the run, the reflux of acid is even more pronounced. A temporary decrease in the tension of the sphincter between the esophagus and stomach can provoke a pushing open of the sphincter and thus the backflow of gastric acid, which is additionally intensified by the increased breathing during physical activity.

Drinking: delicate shortly before the competition
Nausea occurs in long distance running mainly during or shortly after the end of a competition. What is striking is that those athletes who drink something before the competition have a 3.3-times higher risk of upper digestive complaints. The decisive factor for this is the delayed emptying of the stomach, as is observed with higher running intensity (75% of the maximum oxygen intake).

Studies also showed that athletes who had a certain degree of dehydration (about 5% body weight loss due to perspiration loss) had delayed gastric emptying. Thus, dehydration increases the risk of gastrointestinal problems during running, which can lead to nausea and vomiting. Other causative factors are intense heat and long running distances. High outside temperatures can impede gastric emptying by reducing intestinal blood flow and mobility.

Be careful with medications
Typical symptoms such as heartburn and frequent burping are an indication of a dysfunction of the lower esophageal sphincter. An examination by a doctor is therefore recommended. Drugs that attack the gastric mucosa should be avoided as far as possible in consultation with the doctor. The most important points for athletes:

  • Pain killers such as aspirin and ibuprofen should not be taken.
  • Avoid nicotine and drink caffeinated and alcoholic beverages with restraint.
  • Effective drugs (such as ranitidine) or so-called acid blockers reduce acid production and can alleviate the symptoms.
  • Hypertonic drinks (e.g. cola or other sweet drinks) should be avoided because of the resulting delay in emptying the stomach.
  • Isotonic carbohydrate/electrolyte drinks are emptied from the stomach as quickly as water and are therefore preferable in small portions throughout the entire run (commercially produced sports drinks such as gels provide the body with energy without straining the digestion too much).

The art in endurance sports lies in the optimal balance between an intensity of performance at which the necessary amount of energy can still be absorbed and the situation-specific food to which the stomach is accustomed. The appropriate intensity also depends on how ambitious an athlete is. If an athlete runs or goes to the limit for hours in pursuit of a best time, there is a great risk that the stomach will rebel even during minor tasks. If, on the other hand, the athlete consciously avoids this and attaches importance to adequate food, then it is possible that he will make it through the course without any problems and will still have reserves in the end, but will not be able to fully exhaust his performance limit. The “perfect competition” is therefore always a search for the “perfect” speed.

Dr. med. Roberto Llano is a specialist FMH for general internal medicine and sports medicine SGSM. Roberto Llano is a team doctor for the Snowboard Federation, the U15-U20 national football team, the Ju-Jitsu national team and the BMX national team of Swiss Cycling and works as a senior physician at Medbase Bern.

This post is also available in DE.

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