This won’t be relevant to everyone as the occasional jog or HIIT sesh isn’t remotely dangerous, but studies have found that strenuous exercise for over two hours can cause gut problems.
A study published in the Alimentary Pharmacology & Therapeutics journal, based on studies of cyclists and marathon runners, has found vigorous exercise can damage intestinal cells. The digestion problems, which range in severity, can occur if toxic substances get through the injured gastro-intestinal wall and into the blood stream.
It reads: 'With increasing intensity and duration of exercise there was a proportional increased risk of gut damage and impaired gut function.’
The lead author Dr Ricardo Costa said the research confirmed excessive exercise can 'compromise gut integrity and function'.
The team of sports scientists at Monash University in Australia found the problems, which they’ve called ‘exercise-induced gastrointestinal syndrome’, were found when people exercised for two or more hours at 60% of their maximum intensity level. Effects worsened if it was in heat.
Up to 96% of runners who took part in a 24-hour ultra-marathon reported severe symptoms of gut damage, while 93% of mountain ironman triathlon experienced the issues. By contrast, they effected only 7-11% of marathon and half-marathon runners.
So, what to do if your fitness habits put you at risk (e.g. ultra-marathon and ironman runners)? Costa recommends a 'full gut assessment' if you’re experiencing 'gut disturbances during exercise, to ascertain what is causing the issue and to develop individually tailored management strategies.'
He also warns people who have irritable bowel syndrome or inflammatory bowel disease against too much exercise.