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People who exercise very hard may be prone to acute or chronic gut issues, researchers reported.

A systematic review suggested that exercise intensity was a key regulator of gastric emptying rate, with higher intensity exercise (≥70% peak power output) causing the greatest disturbance to gastric motility, according to Ricardo J.S. Costa, MD, of Monash University in Victoria, Australia, and colleagues.

However, steady state moderate exercise (60-70% peak power output or 66% VO_2max equivalent) did not appear to influence gastric emptying and intestinal transit compared with rest in well-trained individuals, they wrote online in .

Additionally, they found that the impact of high-intensity exercise on gastric motility appeared to be ephemeral, as the intensity of prior exercise had a negligible effect on post-exercise gastric emptying rate of a glucose solution.

"Understanding the effect of prolonged strenuous exercise on gastrointestinal motility is important since the consumption of foods/fluids during exercise aids in the maintenance of blood glucoseconcentration and euhydration, aimed at attenuating fatigue and enhancing exercise performance," Costa stated.

The researchers searched five databases -- PubMed, EBSCO, Web of Science, SPORTSdiscus, and Ovid Medline -- to review publications that focused on the impact of acute exercise on markers of GI injury, permeability, endotoxemia, motility, and malabsorption in healthy populations and populations with gastrointestinal diseases or disorders.

They included original field observational studies and laboratory controlled trials from the previous 20 years.

Costa's group found that as exercise intensity and duration increased, so did indices of intestinal injury, permeability and endotoxemia, as well as impairment of gastric emptying, slowing of small intestinal transit, and malabsorption.

Exercise stress of ≥2 hours at 60% VO_2max appeared to be the threshold, while significant GI perturbations manifested, irrespective of fitness status. Running and exercising in hot ambient temperatures exacerbated the indicators of gastrointestinal disturbance, they added.

Additionally, low to moderate physical activity may be beneficial for patients who have irritable bowel syndrome or inflammatory bowel disease.

"Despite excessive exercise being confirmed to compromise gut integrity and function, we have identified several exacerbating factors which can be controlled, and several prevention and management strategies that can attenuate and abolish the damage and compromised function," said Costa.

Two common risk factors included the type of exercise and the duration of the experience.

For example, 96%, 85% and 73% of an ultra-endurance athlete cohort competing in a 161 km, multi-stage, and 24 hours continuous ultra-marathon, respectively, reported severe GI symptoms during competition. Conversely, only 11% and 7% of endurance runners who respectively completed a half-marathon and marathon reported GI symptom.

Hot ambient conditions, being female, eating during exercise, and having a history of recurrent exercise-associated GI symptoms were also linked to greater incidence and severity of symptoms during exercise.

"It is recommended that a full gut assessment during exercise should be undertaken by individuals with symptoms of gut disturbances during exercise, to ascertain what is causing the issue and to develop individually tailored management strategies," said Costa.

Several strategies for preventing or reducing the severity of exercise-associated GI perturbations:

• Maintenance of euhydration
• Consumption of carbohydrate during exercise
• Dietary adaptation of the GI tract pre-exercise
• Avoidance of nonsteroidal anti-inflammatory drugs (NSAIDs)
• Dietary supplementation, such as antioxidants, glutamine, L-arginine, L-citrulline, bovine colostrum, and probiotics

The researchers called for further research on the safety and health implications of prolonged strenuous exercise in patients with chronic GI diseases and disorders.

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