Introducing the Heat Strain Index

CORE recently introduced the Heat Strain Score to measure the cumulative amount of heat strain experienced during a workout or throughout an entire day. To complement that measure, we are now introducing the Heat Strain Index, a real-time metric quantifying how hard the thermoregulatory system is working to keep the body cool.

The Heat Strain Index has a practical range of 0 to around 10, where 10 is an exceptionally high value. That represents a core temperature of 40°C/104°F and a skin temperature of 37°C/98.6°F. A zero is measured in situations when the thermoregulatory system is not strained, including when the core temp is elevated but skin temp is cool (ie. exercising in a cool climate).

In short:

  • The Heat Strain Index is the real-time, minute-by-minute measure of how hard your body is working to stay cool.
  • The Heat Strain Score is the total of the Heat Strain Index values accumulated over a workout or entire day.

Available in the new app

The Heat Strain Index is available in the updated version of the CORE mobile app – find it in either the Google Play Store or the IOS App Store. Tapping the core temp plot on the “Sensor” tab will allow you to see the Heat Strain Index across time, overlayed on core temp and heart rate.

Applications for training

The Heat Strain Index will soon be available on CORE’s Garmin Data Field. This will allow you to view the index live during your workout, giving valuable feedback for pacing and cooling strategies. A lower value means there is little heat strain and that high intensity efforts can be readily handled by the body’s thermoregulatory system (even if the core temp is elevated). A higher Heat Strain Index value, however, suggests strategic decisions about pacing and/or cooling measures should be made to avoid performance decline.