Nausea – Nauseous And Sick Ill Runner Vomiting

Pooping & Puking: Why Extreme Exertion Leads to Surprising Evacuation

BY Patrick Smith

Nothing is worse than a sudden bowel surprise. Here's some valuable advice for your more gastrointestinally-challenged athletes.

What do running, drinking coffee and clocking in for work have in common? They can all trigger a bathroom break. Predictable bowel movements can be a sign of health and a welcome side effect of regular exercise. But not all evacuations are so welcome, and some can be downright unsettling. 

Knowing why your gut responds to training the way it does can help in two ways. First, it is less anxiety-inducing if you expect some gut weirdness. Second, you can use these body signals to gauge when it’s time to dial back the effort. In this article, we will dive into the phenomena of effort-induced gut evacuations. In other words, answering the question, “Why do I get the urge to poop and/or vomit after a hard effort?”

Note: This is not medical advice. The author is a psychology researcher making speculative statements based on published physiology research. If you are experiencing persistent upsetting and/or abnormal gastrointestinal symptoms, please seek medical help.

Striving to Understand Gut Issues

As coaches and athletes, we love to know the causal connections underlying experiences. In the case of gut instability, those connections are not well understood for at least three reasons. The first is a rarity. While GI discomfort is reported in up to 70% of endurance athletes (Steege & Kolkman, 2012), most incidences aren’t extreme. 

Second, is the short-lived nature of these experiences. Anecdotal reports of peak exertion-induced evacuation frequently describe the symptom as a singular event, rarely resulting in an athlete seeking a diagnosis, i.e., “I puked and immediately felt better.” The third is the ethical challenge of human research. While extreme-intensity research has been approved and conducted with mice (Michelucci et al., 2017) and lower-intensity protocols with humans (Pals et al., 1997), the fact that many of those mice died probably prevents independent research review boards from approving human trials.

That said, after investigating the literature from several different directions, we may be able to isolate a few factors contributing to your immediate desire to evacuate after that full-gas effort — pun not intended.

Gastric Ischemia

The harder we exert, the more our body prioritizes oxygen delivery to the working muscles over systems such as the GI tract. At atypical levels of exertion, this can result in localized hypoxia in the smooth tissue of the gut. Cut off the oxygen supply to the gut for long enough, and the barrier cell lining begins to die. At this point, toxic substances from cellular death can result in complications similar to rhabdomyolysis. (Jeukendrup et al., 2000)

Gastric Permeability

In addition to the cell death toxicity described above, as the GI barrier breaks down, harmful substances can cross the normally impermeable gut lining, resulting in immune responses ranging from inflammation to sepsis. (Peters et al., 2001)

Gastric Mechanical Motility

The predominant theory for your everyday ‘runner’s poop,’ which may also contribute to the extreme variant, is, in plain language, vibrations of the gut due to moving around. Walking and running literally shakes the contents down the bowels. Additionally, added blood flow from submaximal effort can increase the frequency of GI muscular activity (peristalsis), further driving the excrement toward the exit. Counter-intuitively, high gastric motility is strongly associated with dehydration and consumption of hypertonic fluids (fluid that pulls liquid from your body). (de Oliveira, 2017)

Core Temperature Spike

Alone, none of the above really addresses the acute severity of the extreme exertion evacuation until we consider the extreme conditions within the body around the phenomenon. At that moment, the body is diverting blood away from the GI, generating an enormous amount of localized heat (>100f in muscle tissue @3cm depth (Girard et al., 2015)), diverting fluids to the skin surface for cooling of said heat, somewhat dehydrated, and beginning to poison itself. This combination reads like heatstroke. A diagnosis commonly associated with uncontrolled bodily evacuation. This conclusion is the most speculative, and there is no reason to believe singular evacuations are heatstroke per se, but it is not beyond reason to suggest that our body would have a similar brief duration response to a hyper-localized dangerous overheating as it would to the whole body overheating.

How is This Useful?

So why do you want to know about this? Primarily to protect you or your athlete’s health. If this emergency evacuation is occurring on a regular basis, the effort needs to be dialed back. At this level of exertion, the body is actually breaking down and poisoning itself. The recovery cost will be more than the adaptation and an athlete runs the risk of inducing physiological protection responses, such as chronic inflammation, that could inhibit their long-term physiological development. Secondarily, preparation. Emergency evacuation is a reasonable bodily response to extreme exertion but can be very surprising and unsettling for an athlete to experience if they are not forewarned. Supramaximal exertions are more common in competition, and experiencing emergency evacuations in that setting is not uncommon.

How to Minimize the Likelihood of Emergency Evacuations

These issues don’t happen suddenly. A few steps can be taken to minimize the possibility of the sudden need for a toilet.

Drink More Isotonic or Hypotonic Fluids

That means water or watered-down fluids. As mentioned above, dehydration exacerbates GI issues. And if the speculation is reasonable, the most effective prevention is making sure your body has the best opportunity to transport heat out of the body. Stay hydrated.

Progressive Intensity Ramp/Heat Acclimation

Of interesting note was that GI issues are strongly correlated with uncommon levels of exertion and/or heat. That is, those who are acclimated to the conditions are much less likely to experience GI distress. If your sport requires atypical exertions or heat for you, build up progressively so your body can acclimate.

Limit Aspirin & NSAID Intake

Throughout the research read for this article, one message could not be repeated enough. Limit or avoid the use of aspirin, even low doses, or other non-steroidal anti-inflammatory drugs. While commonly used for aches and pains, these types of drugs attack the GI lining, resulting in weakened conditions and severely exacerbated damage. (Drini, 2017) If you are regularly taking any of these types of drugs and experience an emergency evacuation, inspect what came out for signs of blood. If there are any, seek immediate medical attention.

Pushing the limits of the human body is embedded in the culture of endurance athletics. It can be very satisfying to reach down deep and see what is possible. But a sudden evacuation can spark unsettling questions about health and what just occurred. With sustainable coaching and preparations such as hydrating, progressive acclimation, and limiting GI-weakening drugs, such experiences can be less likely and less upsetting if they do occur. And with forewarning, the experience can be noticed for what it is, as a bodily signal to back off before long-term damage occurs.


de Oliveira, E. P. (2017). Runner’s diarrhea: What is it, what causes it, and how can it be prevented? Current Opinion in Gastroenterology, 33(1), 41–46.

Drini, M. (2017). Peptic ulcer disease and non-steroidal anti-inflammatory drugs. Australian Prescriber, 40(3), 91–93.

Girard, O., Brocherie, F., & Bishop, D. J. (2015). Sprint performance under heat stress: A review. Scandinavian Journal of Medicine & Science in Sports, 25(S1), 79–89.

Jeukendrup, A. E., Vet-Joop, K., Sturk, A., Stegen, J. H., Senden, J., Saris, W. H., & Wagenmakers, A. J. (2000). Relationship between gastro-intestinal complaints and endotoxaemia, cytokine release and the acute-phase reaction during and after a long-distance triathlon in highly trained men. Clinical Science (London, England: 1979), 98(1), 47–55.

Michelucci, A., Paolini, C., Boncompagni, S., Canato, M., Reggiani, C., & Protasi, F. (2017). Strenuous exercise triggers a life-threatening response in mice susceptible to malignant hyperthermia. The FASEB Journal, 31(8), 3649–3662.

Pals, K. L., Chang, R., Ryan, A. J., Carl, Gisolfi, V., L, K., Chang, R., Ryan, A. J., & V, C. (1997). Effect of running intensity on intestinal permeability. Journal of Applied Physiology, 571–576.

Peters, H. P. F., Vries, W. R. D., Vanberge-Henegouwen, G. P., & Akkermans, L. M. A. (2001). Potential benefits and hazards of physical activity and exercise on the gastrointestinal tract. Gut, 48(3), 435–439., R. W. F. ter, & Kolkman, J. J. (2012). Review article: The pathophysiology and management of gastrointestinal symptoms during physical exercise, and the role of splanchnic blood flow. Alimentary Pharmacology & Therapeutics, 35(5), 516–528.

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About Patrick Smith

Patrick Smith is a Training Peaks Level 2 Coach licensed through USA Cycling. He offers consultations, fully customized training plans, and prewritten training plans you can purchase through the TrainingPeaks plans store. You can learn more at his TrainingPeaks coaching page, his website, or by reaching out.

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