Taylor Knibb Threw Up With 12K to Go and Still Won the Ironman World Championship. Here’s Why Racing Hard Upsets the Stomach

Just past the 30-kilometre mark of Saturday’s marathon in Kailua-Kona, after a 2.4-mile swim and a 112-mile ride, Taylor Knibb walked through an aid station, poured her cold bottle over herself, and came out the other side throwing up. The next time she passed her manager, his whiteboard read: “vomiting is normal.” She was sick again on the way down Palani Road, ran past the defending champion in the final kilometre, and won the Ironman World Championship in 8 hours, 36 minutes and 29 seconds. “Coming out of the aid station, I was vomiting,” she said the next morning on Bob Babbitt’s Breakfast with Bob. “This is 12K to go.”

The whiteboard was right, with a footnote. Throwing up in a race that long, hot and hard is common enough that sport scientists have a name for the syndrome behind it, and data from this very course. Here is what the research says is happening in the stomach of anyone who has felt sick after a hard run, a spin class or a Hyrox.

The race: Three storylines from one afternoon on the Big Island

Knibb, a two-time Olympic relay silver medallist for the US, led off the bike. Heading into the Energy Lab, the out-and-back stretch past the Natural Energy Laboratory, 23 kilometres into the run, she made a decision, she told the post-race press conference: “you need to take care of yourself to get to the finish line.” She walked the aid stations to “take stuff in,” and started vomiting coming out of one. Solveig Løvseth of Norway, the defending champion, passed her at the mile 21 aid station, and Knibb was “also vomiting down Palani,” the hill back into town. Her own theory for that round: “I think it was ’cause, like, of all the force of the downhill.” NBC Sports reported the whiteboard; Slowtwitch’s race report that evening said she “appeared to be vomiting.” Knibb took out the “appeared.”

Løvseth came down Palani almost two minutes clear. A little over a kilometre from the finish she slowed, wobbled and sat down on the road, and Knibb went by. Løvseth got up after several minutes, walked the last kilometre high-fiving spectators, NRK reported, and finished eighth in 9:02:09. “I prioritised my health. People asked me to keep going, but I had to lie down,” she said, in remarks Norway’s VG credited to Swedish broadcaster SVT (our translation). Norway’s sports director, Frode Viberg Jermstad, told VG the athletes raced in 33 to 35 degrees Celsius and about 85 percent humidity, that in his view she had pushed to the limit on just too little food and salt, and that she recovered after a few minutes of being given both. That is a team official’s view, not a medical finding; VG also quoted Løvseth saying she did not know what had happened.

The men’s race went to France’s Vincent Luis in 7:47:27, ahead of Norway’s Gustav Iden. The Olympic champion Kristian Blummenfelt ran in a medal position until the Energy Lab and finished eighth: “Energy Lab, I guess I was a little bit short on liquid. I guess I had enough carbs. I was feeling lack of liquid,” he told Triathlete. And the stomach’s day started in the water. Germany’s Laura Philipp, second in 8:39:34, told the press conference that as the field swam out into the swell, “I got really seasick.”

The blood: Why a hard effort upsets the stomach: the gut lends its blood to the legs

The gut runs on blood, and during a hard effort the body lends that blood to the muscles, the heart and the skin. In a 2001 study in Medicine & Science in Sports & Exercise, Nancy Rehrer and colleagues measured flow in the portal vein, which drains the intestines, in eight healthy men cycling at 70 percent of their maximum; after an hour it was down 80 percent. A 2014 review in Sports Medicine by de Oliveira, Burini and Jeukendrup calls that kind of drop, which comes with intense exercise and is worse when an athlete is low on fluid, one of the main contributors to gut symptoms. It sorts the causes into physiological, mechanical and nutritional, and puts the share of endurance athletes with gut complaints at 30 to 50 percent.

Knibb’s downhill theory fits the mechanical group, by our reading. The nausea part comes from a 2017 systematic review in Alimentary Pharmacology & Therapeutics led by Ricardo Costa at Monash University, which calls the whole picture exercise-induced gastrointestinal syndrome. As exercise gets longer and harder, it found, the stomach empties more slowly and transit through the small intestine slows, so whatever went in sits there longer. Two hours at 60 percent of maximum looked like the threshold, whatever the athlete’s fitness; heat and running appeared to make it worse; and the effect was reversible. Knibb raced for eight and a half hours.

The Kona number: Ironman racers were studied in Hawaii, and their stomachs had the hardest day

The study the whiteboard could have cited was partly done on this course. For a 2012 paper in Medicine & Science in Sports & Exercise, Pfeiffer and colleagues at the University of Birmingham, with Asker Jeukendrup as senior author, surveyed 221 endurance athletes at Ironman Hawaii, Ironman Germany, a half-Ironman, a marathon and a 100 to 150 kilometre cycling race, scoring 12 gut symptoms. Serious symptoms were reported by about 31 percent of the Ironman athletes, against 14 percent in the half-Ironman and 4 percent in the marathon. Athletes with a history of gut trouble had more of it on race day.

Then the trade-off nobody writes on a whiteboard. Carbohydrate intake ranged from 6 to 136 grams an hour across the athletes; those surveyed at Ironman Hawaii averaged 62. In both Ironman races, athletes who took in more carbohydrate reported more nausea and more flatulence, and they finished faster. It is an association from a questionnaire, not a controlled trial, but it describes the bargain every long-course racer makes: the fuel that keeps the legs going is the same fuel a slowed stomach has to deal with.

Researchers argue the bargain can be shifted. Jeukendrup’s 2017 review, Training the Gut for Athletes, calls the gut “highly adaptable”: stomach emptying and comfort can be trained, and a high-carbohydrate diet increases the intestine’s glucose transporters, though he asks for more human studies. A 2025 position statement from Sports Dietitians Australia and the Ultra Sports Science Foundation, written for practitioners, lists carbohydrate and protein during exercise, hydration and gut training among the strategies with mostly consistent benefits, and probiotic supplements among those with negative outcomes.

The heat: Why Kona, and the Energy Lab in particular, makes it worse

Kona adds heat. Jermstad’s 33 to 35 degrees Celsius is 91 to 95 Fahrenheit by our arithmetic, though Slowtwitch called the run kinder than last year’s, with some cloud cover. Either way the body also sends blood to the skin to shed heat. A 2020 review in the journal Temperature by Costa and colleagues, written for athletes heading to the Tokyo Olympics, says heat during exercise “can substantially exacerbate” the gut’s problems, in proportion to the heat stress.

The nausea data agree. In a 2015 study in the Journal of Sports Sciences, Stuempfle and Hoffman surveyed 272 runners from the 161-kilometre Western States Endurance Run. Nausea was reported by 60.3 percent and was the most common symptom among finishers whose race it hurt (86 percent) and runners who dropped out partly because of their gut (90.5 percent). It peaked during “the most challenging and hottest part of the race.” In Kona, by reputation, that part is the Energy Lab.

Fluid sits on top of that. Blummenfelt described running short of liquid, not stomach trouble. But in a 1990 crossover study, Rehrer and colleagues had 16 people drink a carbohydrate solution either well hydrated or after losing 4 percent of their body weight in 30-degree heat or a sauna. Dehydration plus exercise emptied the stomach most slowly of all the conditions, and 37.5 percent reported gut complaints in it, against none in the others. A stomach that empties slowly has more in it when the next gel arrives.

The footnote: Where “vomiting is normal” ends

So the whiteboard was right in the way its author meant: in a race like this, throwing up is common and usually passes. De Oliveira’s review says most exercise gut symptoms are mild and of no risk to health, then names exceptions that can be serious medical problems: bleeding inflammation of the stomach, blood in the stool and ischemic bowel, an injury from lost blood flow. That far end is what poster P0294 at this week’s ACG 2026 meeting looked at: in national hospital records, ischemic colitis was diagnosed in 5.5 percent of hospitalized adults with documented endurance activity against 2.0 percent of similar patients. Its author calls it “a signal, not a verdict”; everyone in it was already in a hospital. None of it is about anyone at Kona.

Heat has its own line. MedlinePlus, the US National Library of Medicine’s medical encyclopedia, lists nausea and vomiting among the symptoms of heat exhaustion and describes heat stroke as a very high body temperature with neurological symptoms such as confusion; the American College of Sports Medicine’s 2021 consensus statement calls exertional heat stroke “a true medical emergency.” That is why races put medical teams on the course, and why repeated vomiting with confusion, or going down in the heat, is a matter for a clinician rather than a whiteboard. Knibb, who sat on the Queen Ka‘ahumanu Highway two miles from the finish a year ago, put her own version of that line simply on Saturday night: “I have to get there safely.”

The rest of us: Throwing up after running, spin or Hyrox: the same physiology at a smaller dose

Most people who have felt sick after a hard effort were not racing for eight hours in the heat, but de Oliveira’s review ties the drop in gut blood flow to intensity. Our reading: a hard interval works the same way at a smaller scale, pulling blood toward the muscles while the stomach slows, so whatever went in beforehand has nowhere quick to go. Timing shows up too: in a small 1992 survey of 55 male half-Ironman triathletes, every athlete who had eaten within 30 minutes of the start vomited during the swim. Our marathon poop explainer, the Chicago gel piece and the Hyrox bathroom rule cover the rest of the gut under the same load.

Facts to carry: Taylor Knibb won the 2026 Ironman World Championship in 8:36:29 after vomiting from about 12 kilometres out, by her own account; in a 2012 study that included Ironman Hawaii, about 31 percent of Ironman athletes reported serious gut symptoms against 4 percent of marathoners, and more carbohydrate went with more nausea and faster finishes; heat and low fluid make it worse; most exercise gut symptoms are mild and pass, while vomiting with confusion in the heat is a matter for a clinician. Nothing here describes any athlete’s health beyond their own public words and their team’s attributed statements. IRONMAN, NBC Sports, Triathlete, Slowtwitch, NRK, VG and the athletes named had no involvement in this article. It is educational, describes what the cited studies and sources say, and is not medical advice.