For the first time since 2019, the professional men and women race the IRONMAN World Championship on the same day in Kailua-Kona. It is also the final stop of the 2026 IRONMAN Pro Series, with 6,000 points on offer to each winner, so the race carries both a world title and a season title. The men start at 6:20 a.m. local time, and by the time the leaders reach the Energy Lab the conversation will, as always in Kona, be about heat, fuelling and who managed both best.

In this post I bring together three things: what the professional race data tell us, what the newest research says about carbohydrate intake during racing, and what we know about heat acclimatisation and the conditions expected on the Big Island.

The data: trends, conditions and predictions

To support this preview I built an interactive Long Distance Triathlons Dashboard, which brings together professional-only results from IRONMAN, IRONMAN 70.3 and T100 racing (sourced from PTO Stats) with race-day environmental data from Open-Meteo. A few design choices are worth explaining, because they matter for how the numbers should be read.

First, split-time trends use the average of each race’s top three finishers rather than the winner alone, with a ±1 SD band. A single winning time is a noisy signal; the top-three average, and the width of that band, tells you both how fast the front of the race was and how close the podium fight was. Second, conditions are matched to performance using WBGT (wet bulb globe temperature) rather than air temperature for the bike and run, since WBGT captures humidity and radiant load, which is exactly what makes a 30 °C day in Kona so different from a 30 °C day somewhere dry. Wind is averaged across the 07:00–16:00 window that covers professional race time, rather than taking a single daily gust. Third, the correlation plots use every individual finisher’s split against the conditions of that race, not race averages, so you can filter by brand and see how the relationship holds up.

The Rankings & Predictions page applies a simple form-based model to the start lists. It is deliberately a heuristic, not a crystal ball: it rewards consistency and recent results, and it cannot know who has been ill, who crashed in training, or who has nailed their heat preparation. It is, however, a useful benchmark against which to judge the race once it is run.

The historical benchmarks are formidable. Patrick Lange’s course record of 7:35:53 in 2024 was built on a 47:09 swim, 4:06:22 bike and 2:37:34 run, and the same race saw Sam Laidlow ride 3:57:22. Lange, now 40, has said this will be his last IRONMAN. In the women’s race, Solveig Løvseth won on her Kona debut in 2025 in 8:28:27, just 35 seconds ahead of Kat Matthews, who set a women’s run record of 2:47:23, with Laura Philipp third in 8:37:28. That race is remembered as much for Taylor Knibb, who was leading with around two miles to go before collapsing – a reminder that in Kona the margin between a world title and a medical tent is thin.

On the men’s side the defending champion Casper Stornes is out after a training crash, which opens the race up. Laidlow arrives unbeaten in four races in 2026, including Challenge Roth and an IRONMAN Lanzarote win by almost nine minutes. Kristian Blummenfelt leads the Pro Series standings, and Gustav Iden, Marten Van Riel (on his Kona debut), Magnus Ditlev and Lange complete a field with four former world champions. Independent modelling by Thorsten Radde at Trirating suggests the leading men share roughly three quarters of the win probability, against about 85% for the leading women – in other words, a surprise is more likely in the men’s race. That is consistent with what I see in the data: the women’s front-runners have more head-to-head history on this course and in these conditions.

Fuelling: how much carbohydrate is enough?

Few areas of endurance practice have moved as fast as in-race fuelling. The 2016 ACSM sports nutrition guidance recommends up to 90 g/h of carbohydrate from multiple transportable carbohydrates (glucose–fructose mixtures) for events longer than 2.5–3 hours. In the field, however, many professionals now report targets of 120 g/h and, in some cases, far higher. Two papers published this year help separate what is supported by evidence from what is enthusiasm.

Morton and colleagues’ review in the Journal of Nutrition (Morton et al., 2026) revisits more than a century of work on carbohydrate and endurance. Their conclusion is that the upper limit of recommended intake could reasonably move from 90 to 120 g/h for trained athletes, since both exogenous and whole-body carbohydrate oxidation can increase at these intakes, with possible benefits for durability and economy. They are explicit, though, that doses of 120–200 g/h seen in the field are not yet substantiated by research, and they propose a more individualised model that accounts for carbohydrate blend and ratio, format, gut training and environmental conditions.

A new study in Medicine & Science in Sports & Exercise (Martyn et al., 2026) tested this directly. Eight trained men cycled for three hours followed by a capacity test, ingesting 10, 90, 120 or 150 g/h (maltodextrin–fructose at 1:0.8, with stable-isotope tracers). Exogenous oxidation rose with dose (1.23, 1.48 and 1.62 g/min at 90, 120 and 150 g/h), but whole-body carbohydrate oxidation was identical at 120 and 150 g/h (2.6 g/min). Exercise capacity was clearly impaired at 10 g/h but did not differ among the higher intakes, and the modelled optimal dose was about 107 g/h (95% CI 92–122 g/h). Just as important, the between-athlete spread in exogenous oxidation was large and grew with dose.

For a Kona athlete the message is practical. Somewhere around 90–120 g/h is where the evidence currently sits; going beyond that is unlikely to add whole-body carbohydrate use and increases the volume of fluid and sugar the gut has to handle. In the heat this matters even more, because splanchnic blood flow is reduced and gastrointestinal distress becomes a major cause of underperformance. Recent work from Monash (Hillemacher et al., 2026) shows that symptom reports alone probably underestimate gut disturbance during exertional heat stress, and a survey at the 2025 Western States 100 (Mougin et al., 2026) found that every finisher under 18 hours had a structured carbohydrate plan, compared with 69% of the slowest finishers, with gastrointestinal symptoms reported by 63% of finishers. The athletes who fuel best on Saturday will be those who rehearsed their exact race-day intake, in the heat, many times beforehand.

Heat: acclimatisation and the Kona forecast

October in Kona typically means highs of 30–32 °C and humidity around 80%, with the lava fields and asphalt of the Queen K adding considerable radiant heat. The ocean is around 25–27 °C, so the swim is non-wetsuit. The National Weather Service forecast issued on Friday afternoon for Saturday calls for sunny conditions with isolated showers in the morning, becoming partly sunny with scattered showers in the afternoon, highs of 84–89 °F (29–32 °C) near the shore, and light winds becoming westerly up to 10 mph in the afternoon, with a 40% chance of rain. Light winds are good news for bike times but bad news for heat dissipation: less convective cooling on the bike and in the Energy Lab means a higher effective heat load, and afternoon cloud and showers could become the most important variable for those still running. On the dashboard you can see how WBGT and wind have related to bike and run splits across previous editions.

The physiology of heat acclimation is well established, but recent studies have refined the practical questions of dose, method and side benefits. A randomised trial in endurance-trained athletes (Snape et al., 2026) showed that just five days of isothermic acclimation in hot, humid conditions (32 °C, 70% RH) lowered resting heart rate by 8 bpm, expanded plasma volume by about 7% and increased sweat loss by around 500 mL during a heat stress test – the classic adaptations that protect cardiac output and thermoregulation on a long day. Renal stress markers were not altered, which is a useful reminder that acclimation improves tolerance but does not remove the physiological cost of exercise in the heat.

Method matters. In well-trained cyclists, six days of post-exercise hot water immersion reduced perceptual strain but did not improve time-trial performance in warm or hot conditions (Kjertakov et al., 2025), suggesting passive approaches are not a substitute for active exercise-heat exposure in already fit athletes. Interestingly, training in the cold while wearing layered clothing reduced perceived exertion and thermal sensation in subsequent heat exposure (Yamaguchi et al., 2026), although without measurable changes in sweat rate or core temperature.

Heat training is also increasingly used for its haematological effects, something the Norwegian group in this field has made very visible. In cross-country skiers and biathletes, adding three weekly heat-suit sessions to a moderate-altitude camp increased haemoglobin mass by 2.9%, compared with 1.2% with altitude alone (Rønnestad et al., 2026), and in elite cyclists five weeks of heat training produced haemoglobin mass gains comparable to a live-high train-high camp (Cubel et al., 2025). In neither study did this translate into clear performance gains, which is an honest caveat: the adaptations are real, but how much they matter on race day is still debated.

The key point, from both the literature and my own experience working in Doha, is that heat acclimatisation is not a single intervention but a process that interacts with everything else: hydration, sodium, cooling strategies, pacing and, crucially, fuelling. Heat increases carbohydrate dependence while simultaneously reducing the gut’s ability to deliver it. The athletes who arrived in Kona early, trained in the conditions and rehearsed their nutrition in that environment will have a real advantage, whatever their power numbers say.

What to watch

If the winds stay light, expect fast bike splits and a large group reaching T2 together, which shifts the race to the marathon and to whoever has managed heat and fuelling best through the first six hours. If the afternoon clouds and showers arrive, they may favour the chasers. And if history is any guide, the athlete leading with 10 km to go usually wins – unless, as Knibb discovered last year, the heat decides otherwise.

Explore the full data, filter by brand and race, and check the predictions at ironmandt100analysis.netlify.app. I will revisit the predictions once the results are in.

References

Cubel C, et al. Haematological adaptations to high-altitude and heat acclimation training in elite male cyclists. Exp Physiol. 2025. doi:10.1113/EP092968
Hillemacher K, et al. The relationship between biomarkers of exercise-induced gastrointestinal syndrome and exercise-associated gastrointestinal symptoms. Sports. 2026. doi:10.3390/sports14060248
Kjertakov M, et al. Limited benefit of repeated post-exercise hot water immersion on exercise performance of well-trained cyclists in warm and hot conditions. Eur J Appl Physiol. 2025. doi:10.1007/s00421-025-06041-4
Martyn HJ, et al. Effects of 10, 90, 120 and 150 g/h CHO on substrate metabolism, exogenous oxidation and exercise capacity: implications for CHO personalization. Med Sci Sports Exerc. 2026. doi:10.1249/MSS.0000000000004176
Morton JP, et al. From metabolism to medals: contemporary perspectives and revisiting carbohydrate guidelines for fueling endurance athletes during exercise. J Nutr. 2026;156(5):101442. doi:10.1016/j.tjnut.2026.101442
Mougin L, et al. Heat preparation and nutrition strategies for a 100-mile ultramarathon in extreme heat: a questionnaire study at the Western States Endurance Run. J Sci Med Sport. 2026. doi:10.1016/j.jsams.2026.05.014
Rønnestad BR, et al. Heat training augments hemoglobin mass during a moderate-altitude training camp in well-trained endurance athletes. J Appl Physiol. 2026;140(5):1298-1310. doi:10.1152/japplphysiol.00777.2025
Snape D, et al. Five days of heat acclimation improves cardiovascular and thermoregulatory responses without altering renal stress biomarkers in endurance athletes. PLoS One. 2026;21(8):e0345346. doi:10.1371/journal.pone.0345346
Yamaguchi K, et al. Short-term endurance training in the cold with layered clothing mitigates perceptual strain during exercise in the heat. Eur J Appl Physiol. 2026;126(10):5543-5552. doi:10.1007/s00421-026-06319-1

Race and forecast information from USA Triathlon, Triathlete, 220 Triathlon, Big Island Now and the US National Weather Service. Literature retrieved via PubMed.