Kona isn’t just a race – it is the proving ground.
The world’s best long-course triathletes arrive on the Big Island hoping to deliver the performance of a lifetime. But every year, even some of the fittest competitors fall short – not because they’re undertrained, but because they misjudge the course, the heat, or their own physiology.
If you want to shine on triathlon’s most iconic stage, you need more than fitness. You need a strategy.
Enter Dr. Dan Plews, a world-renowned exercise physiologist and coach and the current Kona age-group course record holder. In 2018, Dan didn’t just win. In the back half of the marathon, he was running faster than every male athlete on course except for Patrick Lange, the pro men’s champion. It was a masterclass in pacing, cooling, and executing a plan built for Kona’s extremes.
Now, with race day fast approaching, Triathlon Magazine has teamed up with Dan to bring you his science-backed, field-tested insights – the very same principles he uses to coach his own professional and age-group athletes who will toe the line in Kailua Bay in less than two weeks time.
You’ve done the training. You’ve adapted to the heat. Now it’s time to set yourself up to have the race of your life.
The Physiology of Heat Load
In any Ironman, managing your internal physiology is key: you need to understand your thresholds,1 know what pace or power you can sustain,2 and fuel appropriately to stay energized over the distance.3 But in Kona, there’s a critical extra variable: the heat.
Heat load refers to the accumulation of heat in your body.4 And as core temperature rises, your body begins to protect itself through a series of compensatory mechanisms. They’re essential for safety, but they come at a clear cost to performance.
For example, blood flow is redirected away from the working muscles and toward the skin to aid cooling. This helps with thermoregulation, but also reduces oxygen delivery to the muscles,5 making it harder to hold pace or power.
The brain also starts to pre-emptively dial things back. This is known as anticipatory regulation and is part of the central governor theory – the idea that your brain subconsciously limits output to prevent physiological damage. One of the ways it does this is by reducing muscle fibre recruitment as core temperatures climbs.6
What many people forget is that over-heating in Kona isn’t just about the environment; it’s also about you. Your own exertion generates significant metabolic heat, and when that internal load can’t be dissipated (thanks to the Island’s relentless heat and humidity) your body has no choice but to reduce effort, therefore reducing metabolic heat production, as a last line of defense.
But there’s an opportunity here. Understanding these physiological demands – and strategizing accordingly – is exactly why Dan Plews was able to execute an ideal race.
Kona rewards patience, precision, and execution. Dan didn’t just survive the conditions; he mastered them, earning an age-group course record that still stands seven years later.
Swim as Usual – But Set Your Day Up Well
If there’s one leg of the race where heat is unlikely to be your undoing, it’s the swim. Despite Kona’s brutal reputation, race morning conditions tend to be comparatively mild and calm. The air temperature in transition is typically cool, and the ocean is consistent – Kailua Bay usually sits around 26-27°C. That’s warm enough to rule out wetsuits, but not so hot that overheating is a major concern.
There’s no need to adjust your pacing or effort compared to other Ironman events. Instead, focus on efficiency and tactical awareness like frequent sighting and smart drafting to conserve energy.
And don’t forget, you’re racing in Kona! That alone is an extraordinary achievement. So take a moment to soak it in and enjoy it. Stay calm and swim smooth (right around your aerobic threshold is recommended), knowing that the real test – and the decisions that will define your day – are still to come.7
Dan exiting the water, having maintained a sustainable effort close to his aerobic threshold – around a 6/10 RPE.
The Bike: Where Heat Tactics Begin
With the swim behind you, the bike is where Kona’s heat starts to assert itself, and where your strategy begins to matter more.
Thankfully, cycling offers one key advantage when it comes to thermoregulation: convection cooling.8 As you move through the air, the breeze across your skin helps dissipate body heat. The faster you ride, the greater this cooling effect, making velocity a critical (and often underappreciated) factor in managing core temperature.
But there’s a catch. Certain sections of the Kona course – most notably the climb to Hawi – reduce this natural cooling benefit. As your speed drops and your effort increases, you produce more metabolic heat while losing the airflow that normally helps keep your core temperature in check. It’s a combination that can silently begin to erode your performance long before you hit the run.
It’s in moments like these where many athletes make a critical mistake: they push too hard, too early. While hills are often seen as tactical opportunities – especially in temperate conditions – Kona demands a different mindset. Managing what we might call Kona’s “heat tax” is more important than making bold moves mid-race. (Even in the pro race, many tactical moves and attacks are made on the descent after the Hawi turnaround – a reflection of how crucial it is to manage the heat wisely on the way up.)
The graph below reflects core temperature data from one of Dan’s Endure IQ colleagues Dr. Chris Stevens during the Hawai’i 70.3. As expected, his temperature is relatively stable during the swim and increases once the bike begins. Notably, his core temp continues to rise during uphill sections, where speed is lower and power output is higher, and then drops again on descents, where cooling from wind speed increases.
Dr. Stevens, a colleague of Dan’s, tracked his core temperature while racing the Hawai’i 70.3 to gather real-time data in Kona’s unique conditions. As shown in the graph, core temperature remained stable and controlled during the swim. It spiked at the start of the bike and fluctuated with terrain throughout the ride, reflecting the balance of internal heat generation and convection cooling. Core temperature then rose steadily during the run, the most challenging part of the race from a thermoregulatory standpoint. Dr. Stevens walked for about 35 minutes late in the race after surpassing his thermal limits.
The moral of the story? In addition to managing your effort up Hawi and other key climbs, Dan suggests beginning the bike at a rate of perceived exertion (RPE)9 of 6 to 6.5/10, and not exceeding 7/10 by the time you reach T2. He also recommends capping heart rate (HR) at no more than five beats per minute above your aerobic threshold,10 and then using power as a third input – but always backing off if your HR or RPE drift too high, regardless of what the watts say.11
As for cooling? Cold fluids are key. Dan recommends using thermal bottles and/or freezing a portion of your hydration in advance so it’s melted but still chilled when you need it. Dousing yourself with water at aid stations can also be effective, especially on slower, hotter sections of the course.
Ultimately, your tactics on the bike are an investment in the final leg. Because the marathon in Kona doesn’t just test how fast you are; it tests how smart you’ve been.
On the bike, Dan prioritized tactics that set him up for a strong, decisive, course record-worthy run.
The Marathon: Where Smart Racing Pays Off
Kona’s marathon is the section of the race where strategy, pacing, and physiological discipline all come together…or fall apart. If you’ve set yourself up well heading into T2, the run is your opportunity to move through the field with control.
Looking back to the core temperature graph from Dan’s colleague at the Hawai’i 70.3, the pattern is clear: temperatures continue to climb throughout the run. And if your core temp gets too high, your body will force a shutdown. This often means walking – and not just for a few seconds, but for long stretches, especially in Kona’s heat and humidity, where dissipating excess heat becomes incredibly difficult. (Dr. Chris Stevens walked for approximately 35 minutes before he was eventually able to resume running.)
As outlined in a previous Triathlon Magazine article by Thorsten Radde and Dan Plews, the best performances in Kona – delivered by some of the sport’s all-time greats – typically begin with a more restrained opening pace. (Their average pace for the first 3 miles sits below their eventual average for the first 10 miles.) All athletes slow down in notoriously challenging sections like the Energy Lab – a hot, exposed, uphill stretch (low convection cooling) with about 12km to go – but these athletes slow down much less and are able to run well through to the finish.
In contrast, those who have “blown up” – including high-profile athletes like Lionel Sanders and Alistair Brownlee, who were seen walking together on the Queen K in 2019 – often start their marathons too fast and cross the threshold of sustainability. And in Kona’s heat, once you go over the edge, it’s incredibly hard to come back.
Jan Frodeno, Ben Hoffman, and Joe Skipper demonstrate well-paced Kona marathons, finishing 1st, 4th, and 6th in 2019. In contrast, that year Lionel Sanders and Alistair Brownlee opened their marathons faster than the eventual race winner, but slowed down significantly in the later stages.
What does this mean for you? While the opening kilometres of the marathon along Ali’i Drive, with its breeze and flat terrain, often feels like the perfect time to push the pace, it’s crucial to hold back. Aim to run no more than 1.5 percent faster than your target average marathon pace, if at all.
Dan recommends starting around a 7 to 7.5/10 RPE, and not exceeding an 8 by the mid-way point of the marathon. As he tells his athletes: aim to empty the tank by the end, but do it with the grace and steady momentum of a Patrick Lange.
Just like on the bike, you should use RPE as your primary guide, supported by HR. Dan suggests keeping HR at or slightly above your aerobic threshold for the first half of the marathon, recognizing that it will drift up further in the final stages. Importantly, because Kona’s conditions – temperature, humidity, and wind – are always changing year-to-year, flexibility is key. Your pace should respond to how you feel (RPE) and to what your physiology is telling you (HR), not the other way around.
Dan running strong down the hill into the Energy Lab at a pace of 3:54/km. He maintained minimal pace to HR drift throughout the marathon, steadily moving through the field with his trademark controlled execution.
Last but not least, the run is where cooling strategies become absolutely essential for managing core temperature and slowing the accumulation of heat load.12 Dan recommends using every aid station with intention: dump ice down your suit, pour water over your head and face to lower thermal perception and RPE, and store wet sponges in your kit to squeeze over yourself once the initial effects wear off. Cooling gear such as headbands or neck wraps can also help, but you’ll need to carry these yourself, as they won’t be provided on course.
A perfect example of these strategies in action was Chelsea Sodaro’s 2022 Kona win, when she was coached by Dan Plews. She started the marathon in fifth, but steadily moved through the field. Spectators also watched her take her time through each aid station, calmly prioritizing both fueling and cooling, which allowed her to run strong all the way to the finish.
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Race Day is Almost Here: It’s Time to Shine
If you’ve made it this far, you’re not just going to Kona – you’re going prepared. You’ve trained in the heat, and now you’ve studied the strategy that has helped shape age group world records and professional victories.
This October 11th is your time to shine. We’ll be cheering.
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 your approach to race day. 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 Ironman distance is typically raced just above the aerobic threshold; knowing where this sits across swim, bike, and run is essential for pacing (see Endure IQ’s LDT 102 for details).
2. Dan and his colleagues are actively researching “durability” – the way physiological thresholds (and therefore sustainable power and pace) shift over time – as a critical concept in long-course racing. This makes pacing a dynamic, rather than fixed, equation.
3. Another key variable affecting pacing in Ironman is substrate availability (i.e., maximally leveraging both carbohydrate and fat oxidation pathways), since the event becomes metabolically limited over time. (See Endure IQ’s LDT 101 for details.)
4. Heat load is the total thermal stress on your body, combining external and internal factors. External load is driven by the combination of air temperature, humidity, and solar radiation (WBGT), and can be partially mitigated by wind and convection cooling. Internal load comes from metabolic heat produced during exercise. Your ability to cope depends not only on total heat load but also on your heat adaptation: how effectively your body dissipates heat through physiological mechanisms, as outlined in our previous article.
5. It is well-established that, during heat stress, blood flow is redirected from the working muscles to the skin to support thermoregulation. However, some research suggests that in conditions of reduced blood volume (e.g., dehydration), the body may compensate by increasing relative oxygen extraction at the muscles. This highlights that while the physiological mechanisms are clear, the precise impact on performance remains complex and is still being studied.
6. As core temperature rises, the brain reduces motor unit recruitment as a protective mechanism, contributing to the observed decline in power output or pace. While this helps limit internal heat generation, it reduces total work capacity, increases local strain, elevates perceived effort, and accelerates fatigue.
7. While the swim is unlikely to make or break the day for most age-groupers, it still matters. The goal is to exit the water efficiently and with minimal fatigue, which is why a controlled approach is recommended. (In contrast, swim dynamics have become increasingly decisive in the pro ranks, with early breakaways – like Riddle, Van Riel, and Schomberg in Nice 2025 – often contributing significantly to race outcomes.)
8. Dan frequently references this paper by Saunders et al. looking into the impact of convection cooling on heat storage during exercise in hot environmental conditions.
9. Dan typically assesses RPE on a 20-point scale with his athletes and in his LDT courses, but for simplicity, we’ve converted it here to the more common 10-point scale.
10. While RPE offers a valuable subjective gauge of effort, HR provides an objective window into your internal physiology, including the effects of cardiovascular drift as heat stress accumulates. This makes HR a more responsive and adaptable pacing tool than external metrics like power or pace, which don’t account for thermal strain.
11. Research shows a strong correlation between an early rise in RPE and athletes “blowing up” later in the race, highlighting the importance of managing perceived exertion to avoid premature fatigue. Dan emphasizes flexibility while racing in the heat, noting that a given power or pace feels very different (and exerts a different physiological toll) at 33°C versus 36°C. This is why, in hot races like Kona, RPE and HR should lead (power and pace should follow).
12. Testing and practising your cooling strategies during heat adaptation training is recommended. This allows you to observe their effects on RPE, cardiovascular drift, thermal perception, and performance metrics (whether absolute output in a time trial or relative output at a given heart rate), so you can optimize what works best for you on race day.
The post Conquer the Kona Heat: Dr. Dan Plews on Race-Day Pacing, Cooling, and Nailing Your Big Island Execution appeared first on Triathlon Magazine Canada.