The Ironman World Triathlon Championship is legendary for its brutal course conditions. The heat, humidity and wind in Kona, Hawaii can take a heavy toll on even the most elite athletes. The winners of this race are who can put together a fast, consistently paced marathon. Those who start too fast risk spectacular blow-ups; the harsh environmental conditions have reduced many a pro triathlete to a pedestrian-paced jog.
What is one of the major hurdles to a successful marathon in Kona? Overheating.
Smooth pacing and blow ups
Recently, sports scientist Daniel Plews and triathlon data analyst Thorsten Radde analysed Hawaii Ironman marathon splits. In an article for Triathlon Magazine, they examined the consistency of pacing between the first 10 miles and the last 16.2 miles. In 2018 and 2019, the race winners (men and women) ran a marathon that differed in pace by only 3%–7% from the early miles to the late miles. They also found a number of athletes who ran extremely consistently (0%–2.5% pace difference) or blew up (running a pace 20% slower in later miles).
The science of heat stress
To explain these differences, Plews and Radde turned to sports science and the research on heat stress and performance. They drew on the concept of “anticipatory regulation,” which says that the body senses the rate at which its core temperature is rising. If the rate of increase is too high, research suggests that the body foresees danger and automatically reduces power so it does not overheat. This regulation can occur even when the absolute core body temperature is not yet overly high.
Anticipatory regulation may explain the blow ups – the triathletes' core temperatures rose too quickly and their body reacted in self-preservation by slowing down. Or, the athletes overrode early self-regulation signals and overheated into the danger zone, which would also cause a slow down.
The authors suggest that one way we can successfully race in extreme heat is to not start too fast and to be “constantly interpreting our perception of the effort, our perception of the heat, and our heart rate...”
Successful racing with CORE
Athletes who train and race with CORE have an even better option than their perceptions of heat – they can precisely monitor their core body temperature and the rate at which it is rising. Through heat training, they will have learned how to ease into their heat training zone without overshooting into the danger zone. They know how quickly their internal temperature rises in various conditions and at various exertion levels, and they know how much to back off in pace/power to stay at a sustainable temperature.
This means that athletes racing with CORE have the opportunity to cool themselves before they reach a critical temperature that causes a blow up. This cooling might involve external actions (water misting, wet sponges, etc), or slowing their pace. Athletes using CORE can also avoid anticipatory regulation by ensuring that the rate of their temperature increase is sustainable. They will have practised various temperature rate increases in training and will know what their bodies can withstand.
For competitive athletes, slowing down before their body gives up is a tough decision. But in a race like the Hawaii Ironman, blow ups from race leaders are not uncommon. A slower but sustainable pace can rule the day when the impatient and overambitious drop out from overheating. CORE helps athletes reach their upper limit of sustainability – the fastest pace possible without dangerous overheating.