When the Gut Says “Stop”: The Lesson from Beijing’s Hyrox

Yesterday, on 3bikes, we discussed how cycling had shifted from a steak for breakfast to 90, 100, and sometimes 120 grams of carbs per hour. Twenty-four hours later, a story from the Beijing Hyrox serves as a stark reminder of the other half of the equation. Because before carbohydrates can fuel the muscles, a much less spectacular organ must first do its job: the gut.

By Jeff Tatard – Photos: DR

Yesterday, we published an article on 3bikes dedicated to the history of cycling nutrition. From the steak eaten at five in the morning to the 40-gram gels swallowed today at almost precisely timed intervals, it primarily recounted a remarkable shift in mindset. For a long time, athletes were expected to endure hunger. Now, they’re expected to do almost the opposite: to be able to eat a lot while continuing to produce watts.

Then, this morning, I came across a story published by Libération, among others. In Beijing, during a Hyrox event, Australian Joanna Wietrzyk—one of the world’s top athletes in the discipline—suffered a fecal accident right in the middle of the competition. Yet she continued her event. The organizers later acknowledged that they should have intervened more quickly and announced adjustments to how they handle such situations.

The footage, of course, went viral on social media. But behind what some immediately turned into a subject of ridicule lies a much more interesting physiological question: how can an athlete at this level suddenly lose control of her bowels in the middle of a race? And above all, what does this reveal about our new approach to nutrition during competition? This is, in essence, what Nina Voit already explained to us last July, in our feature on the role of the gut in performance: we’ve learned to fuel our muscles better and better, but we’re only just beginning to understand that the gut, too, must be able to keep up.

The body has a hierarchy. And the gut isn’t a priority.

To understand what’s happening, you have to start by putting food aside for a few seconds. When you’re sitting quietly at the table, your digestive tract is working under fairly comfortable conditions. Blood flows to the stomach and intestines; you digest, absorb, and transport nutrients. Now, have that same person run at near-maximum effort, and the physiological hierarchy changes completely.

The muscles demand oxygen, the heart speeds up, the skin must dissipate heat, and the sympathetic nervous system takes over. The body then does what it does best: it prioritizes. A portion of the blood flow that had previously been supplying the digestive organs is redirected to the muscles and the periphery. This is what physiologists call splanchnic hypoperfusion.

During sufficiently intense or prolonged exercise, this reduction in digestive blood flow can become significant. And this is where a rather fascinating paradox of modern sports nutrition begins: at the very moment we ask our gut to absorb 60, 90, 100, or even 120 grams of carbohydrates per hour, we are partially reducing the physiological resources available to it to do so.This was already one of Nina Voit’s key messages last July: “As we increase our energy intake, we’re also asking the gut to work in an increasingly unfavorable environment.”

A muscle that we nourish. An intestine that we mistreat.

Of course, the gut doesn’t stop functioning. But its job becomes more complicated. The reduction in blood flow can disrupt absorption, alter digestive motility, and—when the exertion becomes particularly intense—temporarily compromise the intestinal barrier.

This is where a term that has become relatively popular in recent years comes into play: “leaky gut,” or increased intestinal permeability. However, it’s important to be very precise about this term, because it’s often misunderstood. A more permeable intestine does not in any way mean that stool “passes through” the intestine or that there is some kind of digestive leak in the mechanical sense of the term. It is a microscopic phenomenon involving the cells of the intestinal wall.

Under the influence of factors such as hypoperfusion, heat, and physiological stress, the junctions between these cells can temporarily become less tight. Certain molecules or bacterial components can then pass through the intestinal barrier more easily. This is an important physiological phenomenon, but it does not directly explain fecal incontinence.

To understand fecal incontinence, we must look much further down the digestive tract and examine what happens in the colon, the rectum, and the mechanisms of continence.

Running adds a challenge that cyclists are less familiar with: it’s jarring.

A Hyrox isn’t just an hour spent sitting on a saddle. The format combines eight kilometers of running—divided into eight one-kilometer segments—interspersed with eight functional training stations. You run, push a sled, pull, row, carry, do burpees, weighted lunges, and then wall balls.

From the gut’s perspective, it’s almost a perfect accumulation of mechanical and physiological stresses. Running causes repeated impacts and movement of the internal organs. Burpees, lunges, and certain other exercises cause a sudden spike in intra-abdominal pressure. Meanwhile, the sympathetic nervous system is working at full capacity, and blood flow to the digestive system remains reduced.

This is a major reason why gastrointestinal issues are so common in endurance running: abdominal pain, bloating, nausea, an urgent need to use the restroom, diarrhea, and, in much rarer cases, gastrointestinal bleeding.

The infamous “runner’s diarrhea” is therefore by no means just a locker-room myth. When you run, your digestive system is simultaneously less well-supplied with blood, subjected to more jostling, and exposed to mechanical pressure far greater than that encountered while cycling. As Dr. Laurent Aumont of the IMS Préfontaine explained to us during a consultation, cyclists can sometimes still cope with their digestive discomfort; but runners must also contend with gravity, impacts, and repeated jolts, which add mechanical stress to the physiological strain already placed on the intestines.

And in the case of Beijing, there was probably something else at play.

This is where we must remain extremely cautious. Obviously, we cannot make a medical diagnosis of Joanna Wietrzyk remotely. Several reports from the competition indicate, however, that she may have been ill before the race, possibly due to food poisoning or an infection. And if this information is accurate, it drastically changes our interpretation of the event.

Just imagine an already irritated intestine. Bowel movements speed up, stools become looser, the rectum fills more quickly, and the urge to go becomes much harder to control. Then add an hour of very high-intensity exertion. This reduces blood flow to the digestive tract. Add the impact of running, sudden changes in abdominal pressure, possibly heat, dehydration, the stress of competition, and everything consumed before or during the race.

At a certain point, it’s not necessarily that the sphincter “stops working.” It’s simply that the physiological safety margin disappears.

Continence is, in fact, an extraordinarily sophisticated mechanism. It depends on stool consistency, rectal fullness, the rectum’s ability to distend, the perception of the urge, sphincter function, and the ability to decide whether or not to delay defecation. With normal stools, this system generally has a significant safety margin. With watery diarrhea and an extremely urgent urge during maximum exertion, this margin can become extremely narrow. As Nina Voit explained to us, “Incontinence isn’t necessarily a system failure. It can be the moment when all of its safety reserves are exceeded at the same time.”

So what about those 120 grams?

That’s obviously the question that immediately ties into our article from yesterday. Can eating a huge amount of carbohydrates during exercise cause this kind of problem? Yes, a nutritional strategy that’s poorly tolerated can contribute to certain gastrointestinal issues. But no, consuming 90 or 120 g/h does not automatically cause diarrhea or incontinence.

That’s the subtle distinction. When a large amount of carbohydrates enters the intestine faster than it can be absorbed, some may remain in the intestinal lumen. Depending on the specific molecules involved, their concentration, the amount of available water, and each individual’s tolerance, this can lead to bloating, a feeling of heaviness, abdominal cramps, or diarrhea.

But 120 grams per hour isn’t simply “twice as aggressive” as 60 grams. Modern strategies notably combine different types of carbohydrates, such as glucose and fructose, to utilize multiple intestinal transport pathways and thus increase the total amount of carbohydrates that can be absorbed.

And above all, it’s important to distinguish between two things that are often confused: what we consume and what the body actually manages to utilize.

Nina had already told us about this during the Tour

What’s quite unsettling is that when I saw this story from Beijing, I immediately recalled a discussion we’d had this summer with Nina Voit, founder of *Du Bon Sens dans Mon Assiette*, when we’d dedicated an entire section of our Tour de France feature on 3bikes to this famous gut—which sometimes becomes the weak link in performance.

At the time, we were obviously talking about cycling, not a Hyrox. Yet the mechanism described was already exactly the same. Nina reminded us that a nutritional protocol might make perfect sense on paper but become much less relevant when faced with heat, stress, intensity, dehydration, and the actual state of the digestive system at the very moment it’s being asked to work.

In Part 2 of 4—“When the Gut Becomes the Weak Link”—Nina perfectly summed up the problem: “What goes in isn’t necessarily what gets used.” ” A statement that seems almost obvious when you read it, but is much less so once you start thinking solely in terms of grams of carbohydrates per hour.

Because swallowing a gel doesn’t instantly send its contents to the muscles. It must leave the stomach, reach the small intestine, be absorbed, enter the bloodstream, and become available. Similarly, drinking 750 ml doesn’t automatically mean you’re hydrated. If the stomach slows its emptying or if the intestine is already saturated, some of what you keep sending it simply remains on hold.

Nina actually used this analogy, which we picked up on during the Tour: increasing your intake when your digestive system is starting to reach capacity is a bit like piling more and more packages in front of a warehouse where you’ve just cut back on staff. The boxes keep coming. It’s just that processing them slows down.

She also emphasized another point that takes on particular significance in light of what just happened in Beijing: the same food can be perfectly fine one day and become difficult to tolerate under different circumstances. The recipe hasn’t changed. The body, however, has. A poor night’s sleep, increased stress, a few extra degrees of heat, insufficient hydration, or an already irritated gut can be enough to shift the threshold beyond which things start to get complicated.

And Nina added something that is ultimately very far removed from our modern obsession with numbers: “You can train for a certain capacity, but you mustn’t forget to listen to your body’s response. ” The goal, then, isn’t to break your personal record for carbohydrate intake the way you might aim to increase your FTP. The goal is to build up the maximum amount that’s actually useful and actually tolerated under the conditions in which you’ll need to consume it.

What Beijing demonstrates in an extremely spectacular way—and what the Tour had already shown us, albeit much more discreetly—is that a protocol is never worth more than the body’s ability to carry it out.

Yes, you can train your gut.

That’s probably the most fascinating part of this whole story. For decades, cyclists have trained their legs, their hearts, their VO2 max, their threshold, their lactate tolerance, their aerodynamic position, and even their heat tolerance. But almost no one ever said, “Today, I’m going to train my gut.”

Yet that’s exactly what some elite athletes are doing today. Several studies show that repeated exposure to carbohydrates during exercise can improve digestive tolerance. The digestive tract also adapts to what is regularly demanded of it, even if this adaptation is neither limitless nor identical in everyone.

This ultimately boils down to something very simple: you probably shouldn’t try to consume 120 g/h on the morning of your race any more than you would try out a new pair of shoes at the starting line of a marathon.

You test. You increase gradually. You find the concentrations your body can handle. You determine how much to drink with each intake. You identify which products agree with you and which cause problems. And above all, you replicate this strategy at the intensity at which it will actually need to work.

Because tolerating three gels during a leisurely three-hour run and absorbing 100 grams of carbohydrates per hour during the final third of a race are two completely different physiological challenges. As Cyrille Saillard reminded us, “The stomach and intestines shouldn’t be learning the nutrition plan on the same day your legs are learning what competition is all about.”

The Gut: A New Performance Organ?

This is probably where the story gets interesting for us cyclists. Yesterday, in our article on the evolution of nutrition, we discussed how 100 or 120 g/h had become, for some, a new frontier in performance. But the number itself may not, after all, be the most important part of this revolution.

The real breakthrough likely lies in understanding that eating isn’t enough. You have to digest. You have to absorb it. You have to transport it. You have to tolerate it. And you have to be able to keep doing all of that as the intensity increases, when it’s hot, when fatigue sets in, and when the digestive system is no longer the body’s top priority.

Between the gel we swallow and the watts we produce lies an entire physiological system that we’ve long ignored as long as it was functioning.

We readily talk about a runner’s VO₂ max, their threshold, their FTP, and their ability to repeat efforts. Perhaps we’ll gradually need to start talking about their digestive capacity as well. Because an athlete capable of consuming large amounts of carbohydrates, absorbing them properly, maintaining digestive comfort, and repeating the process hour after hour undoubtedly possesses an additional quality.

A kind of invisible performance. As Martijn Redegeld, nutrition specialist at Visma | Lease a Bike and Brand Manager at AMACX, explained here, “In modern endurance sports, having the legs to consume 120 g/h is no longer enough. You also need a gut that can handle it.”

Perhaps this is our new limiting factor.

The incident in Beijing obviously does not prove that we eat too much during competition. Nor does it in any way prove that strategies involving 100 or 120 g/h are inherently dangerous. On the contrary, Joanna Wietrzyk’s situation seems to show that several factors likely converged in an exceptional circumstance.

But this story serves as a reminder of something that sports sometimes overlook in their quest to optimize everything: the human body is not a machine into which one simply needs to pour more fuel to get more power.

The “tank” still has to accept it. The stomach has to empty. The intestines have to absorb it. Water has to follow. The intestinal transporters have to do their job. And the whole system has to keep functioning even as the body itself would rather direct its resources elsewhere.

Ultimately, this is what Nina was already telling us back in July: the body always has the final say. And two months later, what happened in Beijing reminds us of this in a much harsher way.

Yesterday, we discussed how cycling has learned to fuel the legs. This story may foreshadow what the next step already is: learning to train everything that lies between the plate and the muscles.

Because, at the end of the day, the limiting factor in modern sports nutrition may soon no longer be the amount of carbohydrates we’re able to carry.

But rather, the amount that our gut is actually capable of accepting, absorbing… and utilizing.