About 60% of endurance athletes report gastrointestinal symptoms during training or competition, according to Kayla Henningsen, a PhD candidate researching exercise gastroenterology at Monash University. The American Medical Society for Sports Medicine estimates the prevalence could be as high as 90%. This startling statistic comes to light after Australian athlete Joanna Wietrzyk apologised for soiling herself during the Hyrox games in Beijing on Saturday, an incident that has thrown a spotlight on the common but rarely discussed phenomenon of runner's diarrhoea.
High-Intensity Events Create Perfect Conditions
Wietrzyk won the fitness race but not before using communal equipment with faecal matter visibly running down her legs, muddying Hyrox's reputation. Her case is far more common than many people realise, casting new light on the ominous rows of portable toilets stationed along fun run courses and the knowing nods between runners as they pass them.
Severity varies considerably. "Symptoms can range from mild bloating and cramping through to nausea, diarrhoea and, in rare cases, loss of bowel control," Henningsen says. "High-intensity events such as marathons, ultramarathons and Hyrox can create the perfect conditions for gastrointestinal distress, urgency or diarrhoea."
Not Alone: A History of Public Mishaps
Wietrzyk isn't alone. Other public mishaps over the past three decades include the 1998 London Marathon winner, Catherina McKeirnan, who dodged cameras while suffering several bouts of diarrhoea. Paula Radcliffe, winner of the 2005 London Marathon, was publicly caught relieving herself near the finish line, blaming it on too much gluten-free pasta and grilled salmon the night before.
In 2024, US athlete Taylor Knibb won the Dubai T100 despite having to relieve herself during the race, telling a camera operator: "I just shit myself … so can you not get my ass? Thank you." Although runner's trots are more common in women, men aren't immune. TikTok celebrity Davis Clarke crapped his pants during the 2024 Boston Marathon to avoid a toilet stop impacting his time. In a 50km race walk at the 2016 Olympics, French world record-holder Yohann Diniz suffered stomach pain and had blood and possibly diarrhoea dribbling down his leg before collapsing, yet still finished in eighth place.
Perhaps the most cringeworthy episode afflicted Swedish runner Mikael Ekvall, who ran a half-marathon in 2008 with diarrhoea running down his leg, earning him the viral nickname "bajsmannen" (poop man). He finished in 21st place despite 10km of severe stomach cramps.
An Ancient Ailment with Modern Understanding
The scientific literature has recorded gut problems related to exercise stress, known less colloquially as "exercise-induced gastrointestinal syndrome," for the past century, according to Prof Ricardo Da Costa from Monash University and colleagues. They write that it's likely to have plagued competitive athletes since the ancient Olympics. Despite this, understanding of why and how endurance exercise stresses the digestive tract only started to develop in the 1980s and 90s, and is still relatively unclear, possibly because it can't be pinned to one straightforward cause.
Exercise diverts blood to skeletal muscles, affecting the motility and absorptive ability of the digestive tract. Reduced absorptive capacity can especially affect the lower intestines when athletes load up with drinks, gels and bars during exercise, according to Prof John Hawley from Australian Catholic University. "Events in the heat make the problem worse," he adds, "as blood that would normally go to the gut is diverted to the skin for cooling and to preserve core temperature."
He says prolonged weight-bearing exercise for 90 minutes or more, such as running, can produce more severe symptoms than other endurance-based exercise. "This is because of the vertical up-and-down impact, and why cyclists can tolerate a lot more food and drink." Henningsen refers to this as "mechanical jostling of the intestines" and adds dehydration and intolerance of certain foods or nutrition protocols to these potential causes. Da Costa's team also refers to the gut-brain axis possibly directing performance stress to the gut, potentially through the hormonal stress response and/or the microbiome, among other factors including altered pH.
Prevention Strategies and Training the Gut
From a sports physiology perspective, Henningsen says runner's trots and other gut problems highlight the stress that extreme exercise places on the body: "These events are not necessarily a sign of poor preparation or poor fitness." While risk can be reduced, it may not be completely eliminated, she notes, suggesting prevention strategies such as avoiding unfamiliar foods before a competitive event, staying well hydrated, managing heat exposure and gradually adapting the gut to tolerate carbohydrates and fluids while exercising. Because triggers can differ between individuals, a personalised approach is usually most effective.
Hawley explains that "the gut is an 'athletic organ' and can be trained to tolerate nutrient loading – that is, eating and drinking during exercise – so practise in training what you will be doing in a competition." Henningsen agrees, saying the most important advice is "to treat your gut like any other part of your performance system and train it accordingly." She recommends keeping a record of foods, fluids, symptoms and environmental conditions to look for any patterns.
In addition, Da Costa and colleagues cite evidence that ingesting carbohydrates during prolonged exercise may help. They also review positive findings that proteins, especially glutamine, may support gut integrity and note possible benefits from low-fibre and gluten-free diets, though the evidence for these remains unclear. Fortunately, according to Hawley, "most GI symptoms are mild, transient, and of no risk to long-term health." But Henningsen offers a caution: "If symptoms are frequent, severe or worsening, see a healthcare professional. Persistent gastrointestinal issues should not simply be accepted as 'part of the sport'."
