• CORE 2 Thermal Sensor
• CORE 2 HRM Strap Clip
• Magnetic USB-C Charging Cable
• Product Information Guide
• Fully Recyclable Packaging

Heat Strain Index

Heat strain describes the physiological processes that cool the body. The harder the body works to cool itself, the greater the strain, and the greater the impact on performance. CORE’s Heat Strain Index (HSI) quantifies this strain in real time using an algorithmic combination of core and skin temperatures.

Heat Zones

Your Heat Strain Index can fall into 1 of 4 Heat Zones. The heat training zone (Zone 3) is the one that causes physiological adaptations that improve performance. Time spent in each zone is tracked on the CORE app.

Heat Training Load

Your Heat Training Load is the daily value (on a scale of 0-10) of the amount of time spent in the heat training zone (Zone 3). Optimal heat training involves 2–3 sessions per week, with 45–60 minutes per session in the heat training zone. Sequential days with high Heat Training Load will increase your Heat Adaptation Score.

Heat Adaptation Score

Under the right conditions, the human body has an amazing ability to adapt. The Heat Adaptation Score uses an evidence-backed formula to calculate how adapted you are to heat on a scale of 0-100%. Use Heat Zones to guide your training towards high daily Heat Training Loads, which ultimately boost your Heat Adaptation Score over time.

Core and Skin Temperatures

Core body temperature is the temperature near internal organs in the torso. Core temp rises when we exercise, and if it rises too high, performance suffers. Skin temperature varies widely depending on environmental conditions. While skin temp helps your body regulate core temp, there is often little correlation between the two. Both are used to calculate your Heat Strain Index.

How To Use the Data