TriathlonAnalysis
Two years, two champions on the roadside. What Kona’s last mile does to the human body
For the second year running, the women’s Ironman world title was decided by an athlete who could no longer run within sight of the finish. The science of late-race collapse explains why it happens, and why nobody should guess at the cause from the roadside.
On Saturday, less than a mile from the finish of the Ironman World Championship, Solveig Løvseth was sitting on the pavement. She had led the race moments earlier. Taylor Knibb ran past her and on to the title.
Twelve months ago, on the same road, the positions were reversed. It was Knibb who sat by the roadside in the heat, and Løvseth who passed her to become world champion.
The symmetry is striking, but the experience is not unusual at this race. The defining image of the event’s early years is Julie Moss crawling towards the Kona finish line in 1982, her legs no longer able to carry her, as Kathleen McCartney passed to win. More than four decades on, the final miles on the Big Island still find the limits of the best-prepared athletes in the world.
So what is happening when a world-class athlete, hours into a race and minutes from victory, suddenly cannot run?
First, what we do not know
The honest answer for any individual athlete is: we do not know, and neither does anyone watching on a screen. The reports we reviewed from Saturday’s race gave no medical explanation for Løvseth’s difficulties, and none was given publicly for Knibb’s in 2025. Diagnosis requires a medical assessment, not a camera angle. What follows is what the research says about late-race collapse in general, not an explanation of either case.
Collapse is common, and usually benign, after the finish
Doctors who work at endurance events have a name for it: exercise-associated collapse. In a widely cited review in the British Journal of Sports Medicine, the sports physicians Chad Asplund, Francis O’Connor and Tim Noakes described how most collapses in endurance events happen after athletes cross the line.
The usual mechanism is surprisingly mechanical. While you run, the contracting muscles of the legs act as a pump that pushes blood back towards the heart. Stop abruptly and that pump stops too. Blood pools in the legs, blood pressure drops, and the athlete feels faint or falls. Lying down with the legs raised usually resolves it quickly.
Collapse during the race is different
The same review draws a sharp line: an athlete who collapses while still racing needs to be assessed for more serious causes. The list clinicians work through includes exertional heat stroke, low blood sodium (exercise-associated hyponatraemia), low blood sugar and, rarely, cardiac problems. Many athletes who struggle late in a race turn out to have none of these, but the distinction is why medical teams take a mid-race collapse seriously and why spectators should not draw conclusions.
Why Kona is so hard on the body
Kona combines the factors that make heat dangerous. Racing lasts eight to nine hours for the professional women and longer for most age-groupers. Much of the bike and run takes place on the Queen Ka’ahumanu Highway, across black lava fields that radiate heat. Humidity limits how well sweat can cool the body.
A 2021 review in Physiological Reviews by Julien Périard and colleagues sets out the chain of events: as core temperature rises, more blood is sent to the skin to shed heat, leaving less for the working muscles; sweat losses reduce blood volume; heart rate climbs to compensate. Performance falls long before an athlete is in danger, the body and brain appear to protect themselves by forcing a slowdown.
Add the length of an Ironman, with the fuelling and fluid decisions an athlete must get right for hours on end, and the final miles become a test of whether all of those systems still have something left.
What preparation can change
The 2015 consensus on training and competing in the heat, led by Sébastien Racinais and published simultaneously in three leading sports-science journals, is clear that heat acclimatisation, repeated training in hot conditions over one to two weeks, is the most important protective strategy. A companion review by Périard, Racinais and Michael Sawka describes the adaptations: a larger plasma volume, earlier and more efficient sweating, a lower heart rate and core temperature at the same workload.
The consensus also recommends individual hydration plans based on sweat testing in training, and cooling strategies before and during competition.
None of this guarantees a good day in Kona. But it explains why the athletes who arrive best adapted to the heat, and who pace the early hours with the final hour in mind, tend to be the ones still running on Ali’i Drive.
After her win, Knibb said simply that she “had to learn from last year”. In a race that punishes any error at the very end, that may be the most important preparation of all.
This article is for general information and is not medical advice. Anyone who collapses during exercise should be assessed by a medical professional.
