While racing, core body temperature tends to climb much higher than most athletes experience in training. Unaccustomed to the stresses that come with those core temps, these athletes usually experience major performance loss, and suffer mentally as well.

Core temps often reach and exceed 40° C/104° F while racing. However, the core temps of many athletes only infrequently exceed 38° C/100.4° F while training. While most athletes do plenty of race-specific preparation involving pacing, duration, gear, and fuelling, they usually overlook race-specificity involving core temp. It’s easy to imagine the problems this lack of preparation can cause.

Thermal load

Thankfully, preparing for these higher race-day core temps is a straightforward process. It involves lightly stressing the body’s thermoregulatory system two to three times per week. Raising the core temp into a ‘heat training zone’ accumulates ‘thermal load’, and it enhances performance at higher core temps.

This thermal load does not even need to involve the extreme core temps experienced on race day – it is effective at much lower temperatures (between 38 and 38.5° C/ 100.4 and 101° F for most people). On days when ambient temperatures are not high, athletes may need to wear extra clothing to reach these core temps. But they’re not so high as to cause excessive exhaustion that impacts training.

Tracking thermal load

The new CORE phone app helps you easily track your thermal load. After you set your personalised heat training zone, the app will automatically tally your daily, weekly and monthly thermal load. This lets you optimise training so you’re prepared for the higher core temps you’ll experience on race day.