Collapse During an IRONMAN: Warning Signs and How to Know When to Stop
With less than a mile to go at this year's IRONMAN World Championship in Kona, defending champion Solveig Løvseth was leading by just over a minute. Then she could no longer run. She went down, got back up, and fell again a few steps later. She waved off medical staff and made her way to the finish on foot, in eighth place. Afterward she said she still doesn't know exactly what happened, and that it was probably some kind of overheating. It was the second year in a row that a late collapse during an IRONMAN World Championship run changed the outcome of the women's race.
Twelve months earlier, Taylor Knibb had been in a similar spot. Leading late in the 2025 run, she stopped and sat down on the Queen K highway with about two miles left. She didn't finish, and later wrote that she had completely overheated. This year, Knibb felt herself starting to struggle at 23 km of the run. When Løvseth came past, Knibb let her go. She walked aid stations to take in what she needed, kept moving, and won in 8:36:29. Afterward, she said her 2025 race went wrong when she stopped listening to her body and tried to battle it out with another athlete.
We won't guess at what happened to either athlete physiologically. Neither has reported a diagnosis, and that belongs to them and their medical teams. What the research can offer every age-group athlete is a clear picture of how a collapse during an IRONMAN is evaluated, what the warning signs look like, and how to set yourself up to make good decisions late in a long, hot day.
Collapse After the Finish vs. Collapse During an IRONMAN
Medical teams draw an important line between these two situations.
Most collapses happen after the finish line, and most of those are what sports medicine calls exercise-associated collapse. When you stop moving, your leg muscles stop pumping blood back toward your heart, your blood pressure drops when you stand still, and you feel faint or can't stay on your feet. In their review for clinicians, Asplund, O'Connor and Noakes reported that this condition makes up 59 to 85% of medical tent visits after marathons and ultramarathons. According to the American College of Sports Medicine (ACSM), it usually resolves in less than 30 minutes with rest and the legs elevated.
IRONMAN medical data look similar. At the 2014 IRONMAN South Africa, 7.7% of starters needed medical attention, and 80% of those visits happened after the race. Exertion-related conditions made up most of them.
A collapse during the race is a different situation. As Speedy, Noakes and Holtzhausen put it in their clinical review, "If an athlete collapses during a race, then another serious medical cause is more likely." An athlete who goes down while still racing, or who is confused at any point, needs medical evaluation right away.
Athlete Takeaway: If you feel faint after the finish but are alert and talking, lie down with your legs and hips raised and let the medical team check you. If you or someone near you goes down on course, is confused at any point, or isn't improving within about 30 minutes after the finish, get medical help immediately.
What Can Cause a Collapse During an IRONMAN
Among the causes of collapse the ACSM lists, the most serious are exertional heat stroke, exercise-associated hyponatremia and cardiac arrest. Low blood sugar is also on the list.
Exertional heat stroke
The ACSM's 2023 consensus statement defines exertional heat stroke as a disturbance of the central nervous system combined with a high core temperature, usually above 104°F (40°C). The nervous-system signs are what set it apart. They include confusion, disorientation, unusual or aggressive behavior, loss of coordination, and repeated vomiting. An athlete with heat stroke can still be sweating, so dry skin isn't a reliable sign.
Recognized and treated quickly, heat stroke is very survivable. The National Athletic Trainers' Association describes it as "100 percent survivable" with prompt recognition and treatment, which means cooling the athlete in cold water on site, before transport, with the goal of bringing core temperature below 102.5°F within 30 minutes. That's why large races set up ice tubs at the medical tent, and why accepting help early matters.
Exercise-associated hyponatremia
Hyponatremia means blood sodium has dropped too low, and in endurance racing, the main cause is drinking more fluid than you lose over many hours. The 2015 international consensus statement on exercise-associated hyponatremia reports that almost all symptomatic cases occur in athletes who gained or held their weight during the event. In IRONMAN races, the panel found that up to 18 to 25% of athletes can have low sodium without symptoms, and symptomatic hyponatremia has been reported in up to 23% of athletes seeking medical care at an IRONMAN.
This one matters for age-group athletes, because longer finishing times mean more aid stations and more chances to overdrink. In a study of 488 Boston Marathon runners, those who finished in more than four hours had 7.4 times the odds of hyponatremia compared with those who finished in under three and a half, and runners who gained weight during the race had 4.2 times the odds.
Early symptoms are vague: lightheadedness and nausea. More serious cases bring headache, vomiting, and confusion, which overlap with heat stroke. The consensus panel recommends drinking to thirst, which prevents most cases. It also notes that sodium supplements can't prevent hyponatremia if you keep drinking well beyond your losses. Sodium still has a role in replacing what you sweat out, and our post on sweat testing covers how to plan for it.
Cardiac events
Cardiac events are rare. Across U.S. distance-running races, Kim and colleagues found cardiac arrest occurred in 0.54 per 100,000 participants, or roughly 1 in 185,000. In triathlon, Harris and colleagues compiled 135 deaths and cardiac arrests at U.S. races from 1985 to 2016. Most happened during the swim, 85% involved men, the average age was 47, and the risk was highest among men 60 and older. Autopsies found heart abnormalities, most often coronary artery disease, in 27 of the 61 cases examined.
Warning signs include chest pain or pressure, a racing or irregular heartbeat, unusual shortness of breath, and fainting or near-fainting during or after exercise. In the Kim study, CPR started by a bystander was one of the two strongest predictors of survival.
Low blood sugar
Clinical reviews report that most collapsed endurance athletes have normal blood sugar, so hypoglycemia is a less common cause. A steady fueling plan makes it even less likely. Our athletes target 80 to 120 grams of carbohydrate per hour in long races, and our 70.3 nutrition plan shows how to build up to it.
Athlete Takeaway: Learn the signs of the three serious causes: confusion and loss of coordination (heat stroke), headache, vomiting and confusion after heavy drinking (hyponatremia), and chest pain, palpitations or fainting (cardiac). Any of them is a reason to stop and get help.
Signs That Mean Stop
The hard part is that the signs that matter most can affect your judgment. Confusion is hard to notice in yourself. That's one reason to talk through these signs with your coach, your training partners and your race-day crew ahead of time.
What you notice | What it can point to | What to do |
Confusion, not knowing where you are on course, unusual behavior | Heat stroke or hyponatremia | Stop and ask for medical help now |
Staggering, loss of coordination, legs that won't do what you tell them | Heat stroke | Stop and ask for medical help now |
Repeated vomiting | Heat stroke or hyponatremia | Stop and ask for medical help |
Headache with nausea or vomiting after drinking a lot | Hyponatremia | Stop, get medical help, and tell them how much you've been drinking |
Chest pain or pressure, a racing or irregular heartbeat, unusual breathlessness, fainting | Cardiac problem | Stop immediately and ask for medical help |
Faint or unable to stand after the finish, but alert and talking | Exercise-associated collapse | Lie down with legs and hips raised; let medical staff check you |
If a fellow athlete goes down on course, call for help, stay with them, and if they're unresponsive and not breathing normally, start CPR and have someone bring an AED.
Athlete Takeaway: Know the stop signs before race day and share them with your crew. When any of them shows up, stopping and asking for help is the right decision.
Decide Your Stop Rules Before Race Day
Late in an IRONMAN, after 10 or 14 hours of racing, you won't be in the best position to weigh your options. Make the decision in advance, while you're rested and thinking clearly. There's no published research on pre-race "stop rules," so treat this as coaching advice, but it's advice we give all of our athletes.
Write down your stop signs. Use the table above. Decide now that any one of them ends your day, whatever the clock says.
Share them with your crew. Ask them to watch for confusion or unsteadiness, and agree that they'll flag it to medical staff if they see it.
Accept help early. Medical teams can assess you quickly, and early cooling or treatment makes a real difference. Accepting medical help from race officials is allowed under IRONMAN rules.
Make slow-down decisions before stop decisions. Most good late-race decisions are smaller than stopping: walking an aid station, adding ice, easing the pace, letting someone go. Knibb made those kinds of calls this year. When she started to struggle at 23 km, she walked aid stations to take in what she needed, and when Løvseth came past, she let her go.
Your stakes also differ from a professional's. Løvseth said she didn't want to DNF, and her eighth place also secured second in the season-long Pro Series standings, worth a $130,000 bonus. For an age-group athlete, a DNF costs a finish time and a disappointing day, and the next race will be there. Our post on navigating a DNS or DNF covers how to work through it afterward. Knibb's own story is a good example: a year after her DNF, she won in Kona.
Athlete Takeaway: Write your stop signs down, share them with your crew, and plan to make smaller adjustments (walking aid stations, adding ice, easing the pace) early in the run, before you're forced to make bigger ones.
How to Lower Your Risk Before Race Day
Most of the preparation that keeps you safe late in a hot race is the same preparation that helps you race well.
Prepare for the heat. Our post on heat acclimatization protocols explains how to build heat tolerance in the weeks before a hot race, and our guide to adjusting your pace for heat and humidity shows how to set targets for the conditions you actually get. For what heat and wind look like in Kona specifically, see our Kona course conditions guide.
Cool yourself at every aid station. Ice, cold sponges and water over your head and neck are worth the few extra seconds.
Drink to thirst, and check yourself in training. Weigh yourself before and after a few long sessions. If you gained weight, you drank more than you lost, and it's worth adjusting your plan.
Fuel steadily. A consistent carbohydrate plan supports your blood sugar and your pacing late in the day.
Take cardiac symptoms seriously. If you notice chest pain, palpitations, unusual breathlessness or near-fainting in training, stop and see your doctor before racing. The European Society of Cardiology recommends a physical exam, an ECG and an exercise stress test before high-intensity exercise for adults over 35 who are sedentary or at higher cardiovascular risk. If you're a masters athlete, our post on training over 40 is a good companion read.
Learn CPR. Encourage your crew and training partners to learn it too.
Athlete Takeaway: Acclimatize to heat, pace for the day's conditions, cool at every aid station, drink to thirst, fuel steadily, and get any cardiac symptoms checked before you race.
The Bottom Line
Most collapses at an IRONMAN happen after the finish line and resolve with rest and the legs raised. A collapse during the race, any confusion during or after it, or a post-finish collapse that isn't improving within about 30 minutes deserves immediate medical attention. Know the stop signs, write your stop rules down before race day, and practice the smaller decisions (walking an aid station, adding ice, easing the pace) that let you get to the finish line safely. You can admire an athlete's grit and still race by your own plan.
This article is general education for athletes and isn't medical advice. If you have symptoms, a heart condition or questions about your health, talk with your doctor.
If you'd like a coach to help you build a race plan for heat, fueling and pacing, set up a call with us now, and we will help you be ready for your best race day!
