Three overlapping mechanisms are usually implicated:
1. Blood flow redistribution (“splanchnic hypoperfusion”)
During sustained, high-intensity exercise, the body prioritises blood flow to working muscles, skin (for cooling) and the heart and lungs — at the expense of the gut. Blood flow to the intestines can drop substantially during intense effort. This relative ischaemia irritates the intestinal lining, increases gut permeability, and disrupts normal fluid and nutrient absorption, all of which can trigger loose stools and urgency.
2. Mechanical jostling
The repetitive impact of running physically jars the abdominal organs against each other and the abdominal wall. This is thought to stimulate intestinal motility and contribute to the sudden, hard-to-ignore urge to defecate — one reason lower-GI symptoms are more common in runners than in low-impact endurance sports like cycling or swimming.
3. Altered gut motility and permeability
Intense exercise speeds transit time through the GI tract and increases intestinal permeability (sometimes measured via markers like I-FABP). Interestingly, research suggests these physiological changes occur in most athletes during hard efforts, whether or not they go on to develop symptoms — so susceptibility likely also depends on individual gut sensitivity, hydration status, prior nutrition, heat exposure, and race-day anxiety.
“Runner’s Trots”: The Real Medical Reason Endurance Athletes Sometimes Lose Bowel Control
Why an elite HYROX result made headlines for the wrong reason
This month, Australian HYROX athlete Joanna Wietrzyk became an unwilling case study in exercise physiology after experiencing sudden faecal incontinence mid-race at a HYROX event in Beijing — and going on to win the division anyway. The clip went viral, HYROX’s co-founder publicly apologised for how officials handled it, and the organisation has since flagged new competition rules around health and hygiene incidents.
Beyond the headlines, the episode is a good opportunity to explain a phenomenon that’s far more common in endurance sport than most people realise: exercise-induced gastrointestinal (GI) distress, colloquially known as “runner’s trots.”
It's common — and it's not a sign of poor fitness
Studies of endurance athletes report GI symptoms — cramping, urgency, diarrhoea, nausea — in anywhere from 30–90% of long-distance runners, with lower-GI symptoms like urgency and diarrhoea especially prevalent in high-impact sports like running and, by extension, hybrid events like HYROX. It occurs across all levels of competitor, from recreational runners to elite athletes, and is generally unrelated to underlying illness.
What's actually happening physiologically
Three overlapping mechanisms are usually implicated:
1. Blood flow redistribution (“splanchnic hypoperfusion”)
During sustained, high-intensity exercise, the body prioritises blood flow to working muscles, skin (for cooling) and the heart and lungs — at the expense of the gut. Blood flow to the intestines can drop substantially during intense effort. This relative ischaemia irritates the intestinal lining, increases gut permeability, and disrupts normal fluid and nutrient absorption, all of which can trigger loose stools and urgency.
2. Mechanical jostling
The repetitive impact of running physically jars the abdominal organs against each other and the abdominal wall. This is thought to stimulate intestinal motility and contribute to the sudden, hard-to-ignore urge to defecate — one reason lower-GI symptoms are more common in runners than in low-impact endurance sports like cycling or swimming.
3. Altered gut motility and permeability
Intense exercise speeds transit time through the GI tract and increases intestinal permeability (sometimes measured via markers like I-FABP). Interestingly, research suggests these physiological changes occur in most athletes during hard efforts, whether or not they go on to develop symptoms — so susceptibility likely also depends on individual gut sensitivity, hydration status, prior nutrition, heat exposure, and race-day anxiety.
Why it can escalate quickly, with little warning
Several factors compound the risk in longer, harder efforts:
Critically, once urgency hits during a race, there is often very little warning window between “I might need a bathroom” and loss of control — which is exactly why incidents like this can happen to elite, experienced athletes with no prior history of GI issues.
Practical prevention
The takeaway
What happened in Beijing wasn’t a hygiene failure or a lapse in professionalism — it’s a well-documented, physiologically explainable consequence of pushing the body to its limits under heat and load. It happens to age-group athletes and world-record holders alike.
If anything, it’s a reminder of just how much the gut has to sacrifice to keep the legs moving.
This article is general information and doesn’t replace individual medical advice. If you experience recurrent or severe exercise-related GI symptoms, see your GP or a sports physician.
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