If you’ve qualified for the Ironman World Championship in Kona, congratulations – you have earned your place among the world’s best. But conquering the Island itself? Well, that’s your final challenge.
Kona is known for its scorching sun, high humidity, and little reprieve from exposure. Race day temperatures often rise above 30°C, with a heat index that can feel significantly higher on the asphalt along the Queen K.1 In these conditions, even the best-trained athletes can struggle if they are not prepared.
As Dan likes to joke: “Someone said to me going into Kona, if you don’t take your heat process seriously, you may as well not do any training.”
Research shows that proper heat acclimation can boost performance by approximately 15 percent.2 To put that in perspective, imagine increasing your threshold power, pace, or critical swim speed by that much – it’s a game changer.
With an optimized heat adaptation protocol, paired with a smart race-day plan focused on effective pacing and cooling strategies, you’ll be primed to get the best out of yourself as you power toward the iconic Ali’i Drive finish line.
Getting to Know Dr. Dan Plews: Age-Group World Record Holder, World-Renowned Coach and Sport Scientist
Triathlon Magazine is proud to partner with Dr. Dan Plews on this feature. He is a leading endurance researcher, elite coach, the first age-group athlete to ever break 8 hours in an Ironman event (7:56 at Ironman California in 2023), and the age-group Ironman World Championship record-holder in Kona (8:24 in 2018). Dan also coached Chelsea Sodaro to her professional victory on the Big Island in 2022.3
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We sat down with Dan to explore the science of heat adaptation and how it can help unlock the final performance gains on race day.
Of note, Dan’s journey to mastering the Kona course was not immediate. “I improved from sixth in my age group and a time of 9:12 in 2015 to first overall and a time of 8:24 in 2018,” Dan explains, reflecting on his two appearances in Kona. “And I can point to two things that made the difference – because I didn’t fundamentally change my training. The first: I really dialed in a LCHF [low-carb high-fat] diet, which boosted my fat oxidation. The second: a more comprehensive heat adaptation protocol.”
Even in 2018, Dan recalls how harsh the Island’s conditions initially felt when he began his dedicated heat camp in Hawaii five and a half weeks before the race. “I was doing some reps up Hawi, followed by what was supposed to be a 15km run off the bike,” he shares. “I ended up running only 5km, and I called my wife afterward and told her, ‘I’m not sure how I’m going to get around this course, let alone do well on it.’”
He had of course finished the course before, but that moment of doubt underscores just how brutal Kona’s conditions are, and how crucial Dan’s subsequent heat adaptation process was in transforming struggle into mastery, culminating in his world record performance.
Why Heat Affects Performance
We all know the heat affects our performance – but why?
There are several driving mechanisms. Especially in high humidity environments like Kona, sweating becomes a less effective evaporative cooling mechanism, contributing to a steadily rising core temperature. The body diverts more blood to the surface of the skin to facilitate cooling; however, in doing so, less oxygen-rich blood is available for the working muscles (as well as for the gut – which is why hot environments make athletes more susceptible to GI distress!). GI issues are especially common in Kona, where even top performers such as Gustav Iden and Kristian Blummenfelt were vomiting during last year’s race.
There is also the concept of thermal perception, which refers to the brain’s interpretation of heat stress, and a related phenomenon known as anticipatory regulation. As core temperature rises, the brain may pre-emptively reduce muscular output – forcing us to slow down – to mitigate the risks associated with a dangerously high core temperature.
What can we do about it? Just as we can train fitness, we can also train our bodies to be better able to cope with the heat. An optimized heat adaptation protocol will result in a faster onset of sweating and greater volume of sweat; increased plasma volume to aid in cooling (while minimizing compromises to performance and digestion); and improved thermal tolerance. Basically, we can become more comfortable with feeling uncomfortably hot.
The Science of Adding Heat
How does this look in practice?
Heat adaptation occurs when an athlete’s core temperature is repeatedly elevated above ~38°C, typically for 30 minutes or more, resulting in profuse sweating. This strategic stressor triggers a cascade of physiological benefits,4 but like any form of training, the timing and dosage are key.
The gold standard for heat adaptation is training at the race venue itself, where your body is exposed directly to the specific environmental stressors you will face on race day.5 Dan Plews, for example, completed a ten-day training camp in Hawaii before Kona in 2018, using it as a key part of his preparation. However, for many athletes, this type of travel is logistically and financially challenging.
The good news is that exceptional gains can still be achieved at home through a combination of active and passive heat exposure. Active heat exposure involves exercising in the heat, whether outdoors or via a simulated heat room at home (such as indoor cycling with heaters and reduced airflow). Passive heat exposure – such as sauna sessions or hot water immersion, ideally performed pre- and/or post-exercise – can also play a valuable complementary role.
For professional athletes aiming for the most robust results, blending active and passive strategies is recommended. Age-group athletes, meanwhile, can choose to combine both or rely primarily on passive methods if access to heat camps or DIY heat rooms is not feasible. While passive exposure alone may not deliver quite the same magnitude of adaptation, it remains a highly effective and practical option.
Importantly, heat adaptation should be progressive and closely monitored. Start with shorter, lower-intensity sessions, such as 30 minutes of light to moderate aerobic work, and gradually increase duration or intensity over time. Some athletes may eventually incorporate intervals or sessions up to 90 minutes. Whether using lab testing or field markers, tracking your physiological responses will help to ensure you’re adapting effectively without overdoing it.
Examples of useful metrics during training include heart rate at given workloads, sweat rate, core temperature, and subjective ratings such as perceived exertion and thermal perception. To assess recovery and the ability to cope with the additional heat load, heart rate variability (HRV), general wellness, and recovery scores can provide valuable insight. Together, these metrics converge to provide a holistic view of adaptation and fatigue.
Timing also matters. You’ll want to begin your heat protocol three to six weeks before travelling to the race venue. A common mistake is layering heat stress on top of already high training loads. Instead, align your initial adaptation phase with a slightly lower volume training block, allowing your body to absorb the beneficial physiological changes without compounding stressors.6
A Note of Caution: While heat adaptation can – and does – improve performance, it is crucial to approach it with care. Pushing too hard can be counterproductive, or even dangerous. For example, professional triathlete Kyle Smith spoke openly about having to withdraw from the 2025 Singapore T100 after overdoing his heat prep. His experience highlights an important truth: heat adaptation should be optimized, not maximized.
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Dan Plews’ Heat Adaptation Protocol
To bring these concepts to life, Dan Plews has generously shared the exact protocol he used before his world record Kona race in 2018.
His plan illustrates how a focused, intensive block of daily heat exposure is key to achieving full adaptation. While early adaptations may be present after four to five days for males and around eight days for females, a longer block – ideally around two weeks for males and three weeks for females – is recommended to achieve more complete and lasting benefits.7 Once the initial adaptations are in place, you can return to peak training and maintain your gains with just a few heat sessions per week.8
Dan’s protocol also demonstrates how active and passive strategies can be combined, and how not every session or discipline needs to be done in the heat.9
Dan Plews began with a ten-day heat camp in Hawaii five and a half weeks before race day. During this period, he completed 19 heat sessions across his bike and run workouts. He then returned to New Zealand for a two and a half-week maintenance phase, which included two heat chamber rides and five post-training sauna sessions over 17 days. Dan wrapped up his heat prep with a final seven-day re-acclimatization period in Kona.
Importantly, most of Dan’s heat adaptation took place well ahead of race day, allowing his final build to include sessions in cooler conditions that preserved pace and power, reduced heat-related fatigue, and maintained overall training quality. He also didn’t rely on the taper period to drive adaptation; instead, he used it to gently re-acclimatize while prioritizing freshness and recovery ahead of race day.
From Preparation to Performance
With the Ironman World Championship fast approaching, this is the critical window. There is still time to implement a structured heat adaptation protocol – one that can sharpen your performance and offer a potentially decisive edge over the competition.
But adaptation is only half the story. How you pace and stay cool on race day can also make or break your performance,10 and touched on in a previous article also co-authored with Dr. Dan Plews.
While Kona presents a challenging environment, it is in this crucible of heat and effort that champions are forged. And while the Island humbles many, those who arrive truly prepared – both physiologically and mentally – are the ones who write their names into Ironman history.
We’ll see you on Ali’i Drive.
For a deeper dive into this material, see Endure IQ’s course LDT 103: Optimizing Long Distance Triathlon Training and Performance in the Heat. It provides an overview of all the studies supporting the recommendations in this article – and importantly, offers practical tools to help you individualize and monitor your own heat preparation. You can also check out the Endure IQ Squad and/or 1:1 coaching/consulting with Dan or other coaches for more personalized support.
Footnotes:
1. The wet bulb globe temperature (WBGT) is a scientific measure that combines ambient temperature, humidity, and solar radiation to provide a comprehensive assessment of how challenging it is to compete in a given environment. In Kona, the average WBGT is 24.66, typically ranging from 22.44 to 28.50 depending on the year. According to an ITU “Beat the Heat” resource, this generally classifies the event as moderate risk, with some years potentially falling into the high-risk category.
2. A meta-analysis by Tyler et al. (2016) found that heat-acclimatized athletes generally demonstrate around a 15 percent improvement in performance compared to those not acclimatized. Dan Plews highlights this in his Endure IQ LDT 103 course to showcase the meaningful boost that properly executed heat adaptation can deliver.
3. Notably, Dan Plews coached Chelsea Sodaro during the year of her professional victory in Kona; she has since transitioned to working with a different coach.
4. Emerging evidence suggests that heat-driven adaptations may also enhance performance in temperate conditions, similar to the benefits seen with altitude training. This is an exciting area of ongoing research, in which Dr. Dan Plews and his colleagues are actively involved.
5. The reason training at the race venue is considered the gold standard is not because heat adaptations cannot be realized effectively at home in simulated conditions. Rather, it’s about specificity: the opportunity to measure physiological gains in the actual race environment, to fine-tune pacing and cooling strategies, and to rehearse fueling under the exact conditions you will face on race day.
6. While it’s important to avoid compounding heat stress with peak training loads, not all forms of heat exposure carry the same physiological cost. Exercising in the heat places significantly greater strain on the body compared to passive methods such as sauna sessions. For this reason, it is advisable to begin heat adaptation during a lower-volume training block, with the option to layer in passive strategies earlier or alongside more intensive work as needed.
7. Sex-based differences in thermoregulation influence heat adaptation timelines. Female athletes should also consider menstrual cycle phases and oral contraceptive use when timing heat exposure and assessing adaptation. For more detail, see Dan Plews’ Endure IQ LDT 103 course.
8. Research shows that adaptations from heat training begin to decay at an estimated rate of 2.5 percent per day without heat exposure. This is good news, because it means the adaptations you build early on will be relatively easy to sustain with a few maintenance sessions combined with brief re-acclimatization once you arrive at the race venue.
9. During home-based heat prep (e.g., DIY heat rooms or passive strategies), once-daily heat exposure during the main adaptation block is generally sufficient. Compared to in-person heat camps – where athletes often do multiple daily sessions (though outdoor cycling benefits from wind-driven convection cooling that reduces heat stress) – the controlled home environment can produce more intense heat exposure. As a result, limiting sessions to once per day helps manage heat-related fatigue. Scheduling that session as the final workout of the day further minimizes its impact on other training done earlier.
10. Metabolic heat load is directly tied to pacing: the harder you go, the more heat you generate. In addition to effective pacing, cooling strategies reduce skin temperature, which in turn slows the rise in core temperature.
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