A week ago I published a preview of the IRONMAN World Championship built around my dashboard, the newest carbohydrate research and the evidence on heat acclimatisation. I ended that post by saying that in Kona the athlete leading with 10 km to go usually wins, unless the heat decides otherwise. On 10 October the heat decided otherwise in both races.

In this post I look back at what happened, how the predictions held up, and why a weekend that also gave us a 2:01 marathon in Chicago says a lot about where endurance performance is going: faster on cool roads in new shoes, and increasingly limited by heat everywhere else.

Two races, two collapses, two champions

The men’s race. Vincent Luis won on his Kona debut in 7:47:27, taking the lead late in the marathon and holding off Gustav Iden by 1:36. At 37, and in what is expected to be the final race of his career, he became the first Frenchman to win the men’s title in Kona.

On paper the race belonged to someone else for most of the day. Magnus Ditlev came off the swim in 30th place and more than three minutes down, and still led into T2 after a 4:06:47 ride. By 30 km of the run he was fading, walking aid stations and stopping for extra ice in his cap, and Luis went past him, followed closely by Iden. Ditlev later described it as the lights going out, which is about as good a lay description of exertional heat strain as you will find.

The attrition was remarkable. Sam Laidlow walked early in the run and withdrew, explaining that he had been struggling with iliac artery endofibrosis. Patrick Lange, three-time champion and course record holder, stopped on the bike and pulled out of his final Kona, and Marten Van Riel was seen vomiting on the bike. Kristian Blummenfelt, one of the clear pre-race favourites, faded to eighth. Officiating also shaped the podium: Iden served a three-minute bike penalty, started the run close to nine minutes down and then posted the fastest run of the day, while Matthew Marquardt dropped from first to ninth after his own penalty and fought back to take third.

The women’s race was even more dramatic. Lucy Charles-Barclay led the swim in 51:29, her seventh swim lead in seven Kona starts, and swapped the lead with Taylor Knibb for much of the bike before withdrawing on the run. Knibb, who was sick late in the race, was passed by defending champion Solveig Løvseth with around 4.5 miles to go. Inside the final kilometre Løvseth could no longer run, and Knibb passed her to win in 8:36:29. It was a complete reversal of last year, when Knibb’s own late collapse opened the door for Løvseth, and it came just weeks after Knibb won a fourth 70.3 world title. Løvseth got back to her feet and walked in to finish eighth.

Behind them, two athletes showed what patience is worth in Kona. Laura Philipp came out of the water more than eight minutes behind Charles-Barclay and finished second, winning the IRONMAN Pro Series. Julie Derron took third on her Kona debut despite a three-minute drafting penalty that left her eighth off the bike, and Kat Matthews came from 14th out of the water to fourth.

The podium splits tell the story.

What the data said, and how the predictions fared

Both winning times were well off the course records. Luis was almost 12 minutes slower than Lange’s 7:35:53 from 2024, and Knibb was eight minutes slower than Løvseth’s 8:28:27 last year. The interesting part is where the time went. The run was not uniformly slow: Iden’s run course record from 2022 is 2:36:14, and he ran 2:36:58 after serving a penalty. The fastest bike splits, by contrast, were around 4:06 to 4:11, against 4:06:22 for Lange in 2024. A choppy swim and a hard, humid day redistributed the race, and it rewarded athletes who could still regulate their effort and heat load late in the marathon. On the Long Distance Triathlons Dashboard you can see this in the WBGT-versus-split plots: the run is where the environment exacts its price, and the top-three average hides how wide the spread becomes behind the leaders.

As I wrote before the race, the Rankings & Predictions page is a form-based heuristic built from the results I scrape from PTO Stats and the race-day conditions from Open-Meteo. It cannot know who has a vascular problem, who will be penalised, or whose thermoregulation will fail with a kilometre to go. It also has a structural blind spot: athletes moving up from short course, like Luis, have a thin long-distance history, so any model that rewards consistent long-course form will underrate them. The pre-race consensus had the same blind spot. Triathlete’s preview had Blummenfelt tied with Laidlow for the best odds, and neither made the podium. A model is a benchmark, not an oracle, and Kona remains the race where the benchmark is most often wrong.

So, the next big one is Dubai T100. How is that looking?

Meanwhile on the roads: 2:01 in Chicago, 1:59 in London

The day after Kona, Chicago produced a very different kind of performance. Amos Kipruto won in 2:01:09, the second-fastest time in Chicago history and tied for fifth on the world all-time list, and Hawi Feysa defended her title in 2:13:33, moving to fourth on the women’s all-time list. Two weeks earlier in Berlin, Tigst Assefa ran 2:11:04, a course record and the third-fastest women’s marathon ever, and was still ahead of world-record pace at 40 km before her stride broke down in the final two kilometres. Guye Adola won the men’s race in a personal best of 2:02:50.

All of this sits in the shadow of the London Marathon in April, when Sabastian Sawe ran 1:59:30, the first sub-two-hour marathon in a race that counts for records, and Assefa lowered the women-only world record to 2:15:41, with the top three women all under 2:16 in the same race for the first time.

The common denominator, again, is footwear. Sawe, Yomif Kejelcha and Assefa all raced in the Adidas Adizero Adios Pro Evo 3, a shoe of around 97 g. After Chicago it has won seven of this year’s 12 Major races, and every runner on the Berlin podium wore it. The competition is not standing still: in Chicago, Sharon Lokedi was second in an Under Armour development shoe, and both Brigid Kosgei and Milkesa Mengesha took third in Nike’s unreleased Apex.

The most interesting question is not which shoe wins (it is always the athlete winning and never the shoe!) but how these shoes work, and the geometry is changing faster than the foam. Laurens van Kouwenhove has produced a superb animated analysis of Nike’s progression from the Alphafly 3 to the Alphafly 4 and the Apex, tracing the sole profiles from side-view product photos and a Nike patent drawing.

Rocker geometry of the Nike Alphafly 3, Alphafly 4 and Apex. Analysis and graphic: Laurens van Kouwenhove

Across the three shoes, Nike appears to be moving away from the steep, early rocker:

• The forefoot apex moves back, from 67% to 64% to 61% of shoe length.
• The rocker radius grows, from 45% to 54% to 63% of shoe length.
• The rolling surface extends past the toes, from −7 mm to +2 mm to +8 mm.
• The Apex is zero drop, against 8 mm for both Alphaflys.

The biomechanical consequence is captured in his estimate of the lever arm between the ground reaction force and the ankle, which is a proxy for the load on the calf and Achilles. Early in the roll-over (foot at 10°), the newer shoes shorten the lever arm: 132 mm for the Alphafly 3, against 121 mm and 125 mm. Late in push-off (foot at 45°), the order reverses: 142 mm, against 155 mm and 158 mm. In other words, the shoe appears to “hold on to the lever” for longer, shifting plantarflexor demand later in stance rather than simply reducing it.

Van Kouwenhove is careful to say these are indicative values from an unloaded, rigid-sole model. A real sole compresses, and the foot is not a rigid lever. But the direction of the change is plausible, and it matters. Much of the debate about super shoes has focused on energy return from foam and plates. Geometry that alters ankle moments could explain why benefits vary so much between runners, and why some athletes report calf and Achilles problems when changing models. A zero-drop shoe with a longer late lever arm is not a neutral swap for someone who has trained for years in an 8 mm drop.

This is also directly relevant to triathlon. In the last 10 km at Kona, calf fatigue and form breakdown are exactly where races were lost this year. How a shoe distributes load across a 2:40 to 3:00 marathon, run after five hours on the bike, is a question nobody has studied properly yet.

I want to be careful here, because “super shoes” have become a lazy explanation for everything. There is still no precise answer to how much the curved plate and resilient foam benefit the elite marathon runner, and the gains appear to vary between individuals. Pacing, fuelling at 90 to 120 g/h, deep Ethiopian and Kenyan talent pools and cool, flat courses all contribute.

But there is a more important point for this post. These times are produced in cool conditions. Kona showed what happens to the same physiology at 30 °C and high humidity. The next marginal gains in endurance sport may come less from returning energy at the foot and more from removing heat from the body.

Cooling clothing: from F1 cockpits to tennis courts and trails

This is where the sportswear industry has been moving fast in 2026, and two companies have taken quite different approaches.

Fabric that changes the microclimate. In June adidas launched CLIMACOOL+, built around a 3D, body-mapped embossed fabric whose raised structures hold the garment off the skin so that air can circulate and sweat can evaporate. The structures are mapped to the chest, upper abdomen, shoulders and upper back, the areas identified through physiological data capture and climate chamber testing. Interestingly for the marathon story, adidas says Sawe ran his sub-two-hour marathon in a singlet featuring the technology.

Nike’s Radical AirFlow is a nice piece of applied fluid dynamics. Inspired by the Venturi effect, the material uses funnel-shaped airducts that capture air as the athlete moves forward and accelerate it towards the skin to speed up sweat evaporation. In Nike’s climate chamber testing, prototypes retained 50% less sweat than Dri-FIT after prolonged running in the heat, and thermal manikin tests showed 25% lower resistance to the evaporation of sweat. Caleb Olson wore a prototype when he won the 2025 Western States 100 in the second-fastest time in the race’s history.

Active cooling between efforts. The second adidas initiative is quite different. The CLIMACOOL System was first developed for the Mercedes-AMG PETRONAS F1 drivers to cope with cockpit heat, then deployed across adidas partner federations at the 2026 FIFA World Cup, and has now been rolled out to tennis players in New York. It consists of a vest containing a gel frozen in portable freezer units, worn over normal kit, plus neck pieces for changeovers, set breaks and practice. Adidas reports a significant cooling effect after three minutes, and an effect lasting up to an hour after 10 to 15 minutes of use.

A few observations from a physiologist’s point of view.

First, these are two different problems. Garments like CLIMACOOL+ and Radical AirFlow try to improve heat loss during exercise by increasing air movement and evaporation at the skin. Vests and neck collars are pre-cooling and between-bout cooling tools, which suit intermittent sports like tennis and football, or the warm-up before an endurance race. The evidence that both pre-cooling and per-cooling improve performance in the heat is reasonably solid (e.g., Bongers et al., Br J Sports Med, 2015). Ditlev stuffing ice into his cap at 30 km was per-cooling in its most basic form and something you should do (I do!) in every hot race no matter how you feel at every water station [keep the body as cool as possible].

Second, the environment limits what fabric can do. Evaporation depends on the vapour pressure gradient between skin and air. In dry heat, more airflow over wet skin is very effective. In Kona’s humid air the gradient is smaller, so the gain from any garment is smaller too, although increased air velocity still helps convective heat loss. Relative air speed also matters: these garments should work better at 20 km/h on the run than at a walk, and on a bike at 40 km/h the airflow is already high.

Third, the numbers so far are manufacturer data. Fifty per cent less sweat retained and 25% lower evaporative resistance are meaningful material properties, but they are not yet independent, peer-reviewed measurements of core temperature, heat storage or performance in athletes. I would very much like to see these garments tested in proper heat-stress protocols, ideally in the kind of humid conditions that undid Ditlev and Løvseth.

What Kona 2026 teaches us

The lesson from the Big Island is the same one the literature keeps telling us: in the heat, the winner is often the athlete whose system fails last, not the one with the biggest engine. Fuelling, heat acclimatisation, pacing and cooling interact, and failures in any one of them show up in the final hour. Luis and Knibb were not the strongest athletes on paper for the whole day, but they were still running when it mattered showing that their bodies and most of all their strategies worked. If you want to read more about Kona, there is a very interesting pre-print here from 3 excellent sports scientists (and triathletes): Heat, wind, and the calendar: why a warming climate makes its performance effects unidentifiable at the IRONMAN World Championship. They have updated it now to version 3 and have also created a very nice Ironman Hawaii Predictor for age groupers based on historical data as part of the research paper. The tool is available clinking on the link below:

https://ironman-hawaii-predictor.com

Meanwhile, on cool flat roads, the marathon keeps getting faster with every new generation of shoes, and as the rocker-geometry analysis shows, not only because of foam. As temperatures at major championships rise, I expect the next wave of innovation, and the next wave of controversy, to be about thermal technology. That makes it all the more important that brands publish their data and that we as scientists test these claims independently.

Race and results information from Slowtwitch, TRI247, Triathlete, Big Island Now, NBC Sports, FloTrack, Marathon Handbook and Find Your Edge. Product information from adidas and Nike press materials. Rocker-geometry analysis by Laurens van Kouwenhove.