A Hyrox race in Beijing has sparked an awkward but surprisingly useful conversation about what extreme exercise does to the human gut. Australian athlete Joanna Wietrzyk developed diarrhoea mid-race during the Hyrox Beijing Women's Pro event, was allowed by officials to keep competing, went on to win — and organisers have since apologised, with co-founder Moritz Fürste admitting the event made a mistake by not reacting immediately. New rules and procedures are now in place.

The incident divided opinion online, but it's far from unique. British marathon great Paula Radcliffe famously stopped by the roadside during the 2005 London Marathon to relieve herself in front of spectators and cameras — and still won in 2:17:42. As one ultra-runner puts it, for endurance athletes it's not a matter of if this happens, but when.

Sports dietitian Dr Rachel Scrivin, who completed a PhD in exercise gastroenterology, explains there are three main reasons the gut rebels during hard efforts. First, blood gets diverted away from the digestive system toward working muscles and the skin for cooling, which can compromise the gut lining in events longer than three hours or in heat. Second, hormones like adrenaline and cortisol change how fast things move through the intestine — hence the familiar pre-race nervous poo. Third, there's simple mechanical jolt: Hyrox is especially brutal in this respect, alternating upright running with burpees and other movements that churn the gut.

Crucially, there's a difference between the common urge to go (the most reported symptom in Scrivin's research) and actual incontinence, which is rare and, if it happens without warning, worth investigating with a doctor. Most athletes get an early signal and can hold on; marathon routes are lined with portable toilets for a reason. Ultra-runners heading into the wilderness routinely pack gloves, wet wipes and a sealable bag.

There's a mental angle too. High-performance psychologist Iain Saunders notes that elite athletes are praised for overriding their bodies' signals — the same trait that let Wietrzyk push through also made it hard for anyone to stop her. He argues organisers, not competitors mid-effort, should carry that responsibility, pointing to rugby's concussion and blood protocols as a model. Hyrox already penalises spitting and littering, which makes the lack of intervention here all the more glaring.

For anyone lining up for a Hyrox, marathon or long training run, the practical advice is straightforward. Eat easily digested, low-fibre food beforehand — rice, pasta, potatoes, kūmara — and consider a low-FODMAP approach in the 24-48 hours before a big event. Sip rather than gulp fluids in the final 30 minutes, since fluid hitting the stomach stimulates the bowel. And practise your race-day nutrition exactly as you trained with it, because changing fuel mid-race is like an F1 team experimenting on race day. Many experienced athletes even build a toileting routine: breakfast, some fluid, and a relaxed toilet visit about two hours before the start.

The takeaway? Gut emergencies are a normal, discussable part of endurance sport — and knowing why they happen, and how to plan around them, beats pretending they don't exist.