“If you can’t stand the heat, get out of the kitchen.”
We’ve all heard the saying. It applies to many things in life, but nowhere is it more literal than in endurance racing. And there’s a scary question most athletes don’t even think they need to ask themselves: What if your high level of fitness actually prevents you from knowing when to get out of the kitchen?
Most endurance athletes are now familiar with heat acclimation. Historically, this was a niche prep phase of training. It was something a triathlete might do for a short, 4-6 week block before an extremely hot and humid event, such as the Ironman World Championships in Kona, Hawaii. It was short-lived and event-specific.
Recently, however, there has been a massive shift. Professional and amateur athletes, alike, are now incorporating heat training into their regular routines, regardless of whether their next race is in a desert or a cool climate. Why the sudden change? Is heat training here to stay, or is this just the next hot fad (no pun intended)? The science is clear: heat training offers massive physiological benefits beyond just surviving the heat of battle.
The Hidden Benefits of Heat Training
Even if you are racing in cool weather, heat adaptation has some pretty significant performance benefits. Some of the key adaptations include:
- Increased Blood Plasma Volume: Heat exposure stimulates the body to increase its plasma volume. This boosts total blood volume, enhancing oxygen delivery to muscles even in lower temperatures. This results in improved cardiac output and a higher VO2max.
- Cooling System Efficiency: Heat acclimation trains your body to sweat earlier and at lower core body temperatures. It also helps sweat glands conserve electrolytes (like sodium), preventing dehydration and cramping.
- Lower Heart Rate: As your body adapts, the heart rate required to sustain a specific workload drops, significantly reducing overall cardiac strain.
- Improved Fat Adaptation: Heat adaptation can reduce the rate at which muscles burn glycogen, forcing the body to rely more on fat oxidation, a critical energy system for long-course events like Ironman, ultra marathons or extreme triathlons.
- Mental Toughness: Let’s be honest, training in the heat is miserable. Whether it’s active heat training or passive heat training, like a sauna session or hot soak, it requires immense mental focus. This builds the mental toughness necessary to push yourself to new levels of fitness in training, or to endure dark moments on race day.
The Paradox of Fitness: When “Feeling Good” is Dangerous
Being heat adapted is clearly a competitive advantage. However, as a CORE Coach who is invested in training with and coaching athletes using CORE’s core temperature sensor, I’ve noticed a dangerous downside that often goes overlooked: Extreme fitness can mask the warning signs of heat illness.
We tend to assume that if we are overheating, we will feel it through the well known symptoms of heat illness: dizziness, cramping, a spike in heart rate. But, for highly conditioned endurance athletes, this isn’t always true. High aerobic fitness creates a “perfect storm” where your body continues to perform efficiently even as your core temperature climbs into the danger zone.
Because you are so fit, your body may not trigger the usual alarms that would alert you to the threat of heat illness. You might feel great, with no performance degradation, right up until you cross the physiological point of no return. We saw this in Kona at the 2025 Ironman World Championship with some of the world’s top pros, Taylor Knibb and Lucy Charles-Barkley. Despite being some of the fittest humans on the planet, who had also both invested heavily in heat training prior to Kona, their bodies shut down. They likely didn’t feel that they were in danger until it was too late to reverse it.
Surviving Ironman 70.3 Malaysia
I can say from firsthand experience that monitoring your core temperature when racing in extremely hot and humid conditions, can be the difference between a finisher’s medal and a hospital bracelet.
Last November, I raced Ironman 70.3 Malaysia, the hottest and most humid race of my life. The conditions were brutal: 90°F+ (32°C+) air temperature, 100% humidity, and 87°F (30°C) water temperature. Coming from a cold Wisconsin autumn, I knew I was at risk of heat related issues.
I made a conscious, tactical decision: I would run with only my CORE sensor’s core temperature data displayed on my Garmin watch. No pace. No power. No heart rate. I was going to run based on feel, but monitor my core temp and let that data be my governor.
This decision likely saved my race, and possibly my life.
Within the first 2-3 miles of the run, my CORE sensor showed I had already exceeded the threshold for severe heat illness. The scary part? I felt amazing. My heart rate was low, my legs felt fresh, and I was chatting with other athletes. My fitness was masking the reality of my internal physiology.
Because I trusted the data over my feelings, I forced myself to back off on the pace. At the halfway point of the half marathon run, I made the decision to start walking through every aid station to completely douse myself in ice and water, even though I didn’t feel like I needed that break. Surprisingly, those cooling methods still didn’t lower my core body temperature, but it did prevent it from climbing further into the danger zone.
Sure enough, at mile 10, the reality caught up to the data. I went from feeling absolutely fine to dizzy and disoriented almost instantly. Because I had pulled back four miles earlier based on the CORE sensor data, I was able to manage the symptoms and finish the race. Had I continued to push based on “feel,” I would have run myself right into a Malaysian hospital, and that’s not really where I hoped to spend my post-race vacation time.
Train Smarter, Not Just Hotter
Heat illness is not a joke. And for an extremely fit athlete, it can be a silent assassin.
As heat training becomes a staple in our regimens, we must pair that adaptation with monitoring. Using tools like the CORE Temperature Sensor allows you to see what your body isn’t telling you yet. It gives you the chance to implement cooling strategies before your system shuts down, ensuring you live to race another day.
However, integrating heat protocols is not as simple as just buying a sensor or sitting in a sauna. It requires specific timing, precise intensity control, and expert data analysis to ensure you are gaining fitness and not just digging a hole of fatigue or becoming extremely dehydrated.
This is where coaching makes the difference.
As an official coach in the CORE Coaching Network, I help athletes safely integrate heat training into their schedule. I use the data from the CORE sensor to build heat adaptation strategies that are tailored to your specific physiology and race goals without putting you at risk of performance degradation, excessive fatigue or heat illness.
If you are ready to unlock the benefits of heat training, and want to do it safely, don’t leave it to a guessing game. Reach out to me at Tussle Endurance today. Let’s look at your data, build your heat map, and get you ready to perform when the temperature rises.
