Using the CORE Temperature sensor to optimize training & racing in the heat.
Since 2021, I've been using the CORE Body Temperature sensor in my training and, subsequently, incorporating it into the programs of some of the athletes I work with. Initially, my curiosity revolved around how or if the CORE could help the athletes racing in hot weather conditions (like Kona).
When using tools like this in training, I'm much less concerned about the absolute accuracy that other devices may need such as in research conditions requiring a high level of resolution. In training, I look for a reliable device that produces uniform data that may help detect trends over time.
In this case, my primary concern wasn't whether the CORE delivers the same precise data as say, an ingestible thermometer pill but more to see if the device provided dependable & repeatable data. After tracking data in similar conditions for months, I felt confident the data would be useful and suit my needs.
In fact, last year, I used the CORE device it in my preparation for Ironman Waco and we also used it in Jana's training, and it was an important preparation factor in winning her 2nd AG world title. Therefore, for 2023, we kept exploring if there were other ways to use the CORE data to optimize her training further.
With the in mind, we started with how the CORE is most commonly used; to determine her heat training zones via ramp tests (bike and run). This gave us a starting point, but since the ramp test "heat training zone" occurs at intensities above the Ironman race pace, we tracked her core and skin body temperature for all rides (over 4 hr) and runs (over 1:30 hr) in hot conditions, to learn her optimal Ironman heat range.
This approach allowed us to test the boundaries of what pace and power were sustainable in race-like weather conditions & helped us determine the highest sustainable power/pace while maintaining the body's core temperature steady state without affecting performance.
Well also tracked how her body's core temperature and Ironman race pace changed depending on varying hot weather conditions (from 80-105F), different humidity levels (40-80%), and even when training at high altitude in the heat. We learned how despite adapting to the altitude, dry heat affected her performance further more than when training under very humid conditions. In those instances, hydration was key to maintain core temp and proper heart/power/pace levels.
All this helped us distinguish whether pacing or fueling/cooling needs were more important for various conditions . This was very important As Jana trained through the Texas summer heat and we experienced 45 days of triple-digit temperatures. With such extreme weather, she often trained by heart rate & monitoring core temperature versus just chasing race power or pace targets. At times she had to back off her intensity to allow both HR and core temp to decrease while focusing on fueling/cooling. This allowed us to keep the extra physiological strain from the heat under control to avoid delaying her recovery or worst, experience significant training setbacks.
Also, we dialed in her hydration and fueling plan with the data, as maintaining proper hydration levels helps modulate the body's core temperature. In general, as we dehydrate, the core temperature & heart rate will gradually rise while our pace/power drop. Anytime she felt behind in her fueling, we could see how it affected her performance, i.e., later on during a ride or a run off the bike.
Furthermore, we dial in optimal "cooling" strategies by tracking body core & skin temperature. When Jana followed a cooling strategy (i.e., constantly dumping water on her torso), her skin temperature remained stable. Therefore, the core temperature remained stable without affecting heart rate and pace/power.
The opposite occurred when the cooling plan was "off." Skin temperature was more unsteady, leading to higher core body temp & heart rate and either a drop in power/pace or affecting the run when this occurred during the bike.
The CORE also taught us how body core temperature was affected after swimming. In the example below, the file is for Jana's final race simulation performed in Kona 14 days before race day. The simulation included a 25-minute open water easy swim, followed by riding the entire bike course and a 12-mile run. And though the CORE doesn't record while swimming, she wore it to track her core temperature right after swimming.
As you can see, her core temperature was relatively high after the swim. It peaked at 101.6 F (38.7C), higher than her Ironman heat range. The temp gradually declined to her regular Ironman heat range levels over the next hour. This taught us that in addition to starting her fueling on the bike immediately, she also needed to begin her cooling strategy to bring her core temperature down to normal.
Finally, the CORE allowed us to test how different equipment/gear choices could affect body temperature. For instance, her body core temperature changed significantly when using two different aero helmets. With one, her temperature remained within her usual Ironman heat zone, while with the other one, her core temperature skyrocketed to some of the highest temperatures we saw all year.
In summary, the CORE Body Temperature sensor has become a valuable tool to collect practical data to inform the training of our athletes. Specifically, this tool helped Jana to prepare better and ultimately conquer her 3rd AG world championship as we managed to:
Identify proper Ironman heat zone & track sustainable power/pace targets
Dial in her pacing, fueling and cooling strategies
Determine how the heat & humidity impacted her training and recovery in various conditions. (ie. altitude training)
Manage heat training load & most importantly, recovery (in the TX summer)
Identify how her core temperature was affected after swimming
Test different gear/equipment and how it affected body core temperature.
I’ll keep collecting data and exploring more practical ways to use it in our athletes' preparation in the future, but for now, I believe the strategies discussed here can add significant value to an athlete’s training program, more so for those racing in hot weather conditions.