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The CORE sensor

The CORE sensor

Trusted by athletes, coaches & sports scientists

3 total reviews

Regular price 3,499.00 NOK
Regular price Sale price 3,499.00 NOK
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For customers outside Norway tax is not included and may be charged in customs.

The CORE body temperature sensor will give you real time view of your core temperature.

Through the live view of your core temperature and the additional help of the Heat Strain Score and of the Heat Strain Index, this sensor is the optimal tool for heat training. 

Why heat training? 

The obvious gain is to optimize heat acclimatization for competitions or even training camps in hot and humid conditions. The equally important use is simply managing heat training to increase your efficiency and in turn your base endurance and performance at race day.


Also, reduce chances of dehydration, overheating, fatigue, and heat related injury.


Heat adaptation

Adapt to the climates you are training and competing in through heat acclimation and heat training, and learn how to hydrate before, during, and after the workout and competition. Use real-time data feedback to prevent dehydration, so that you don't overheat, get fatigued, or get injured.

Used by the best

Olav Alexander Bu, the coach, scientist and researcher behind Kristian Blummenfelt and Gustav Iden, says that “being able to manage temperature is very important in training and competition”. Get a more intuitive understanding of your body by using the Core sensor. Find your phase and control your intensity with core body temperature data.

How it works

The CORE temperature sensor is not a thermometer. It measures your core temperature indirectly from non invasive body skin temperature and thermal power production (heat flux). Using the Core sensor will give you a better understanding of hydration before, during and after exercise. It will also give you an competitive advantage in long distance competition and when competing in hot and humid climates.


The sensor is usually worn by fastening it to a conventional heart rate belt, or with custom adhesive patches.

The sensor can easily pair up with a smartphone, Garmin, or other smart watches.

What is the Heat Strain Score?

Heat Strain Score

CORE’s Heat Strain Score measures the cumulative amount of heat strain experienced during a workout or entire day. It is a function of the amount of time that both core and skin temperatures are elevated, and it indicates how hard the thermoregulatory system is working. The longer that both temperatures are elevated, the higher the Heat Strain Score will be. The higher the Heat Strain Score, the more performance degradation an athlete can expect.

For example, if an athlete does two 60-minute workouts at the same core temperature, the Heat Strain Score will be higher for the workout where skin temperature was higher. This is because it is harder for the body to shed heat when skin temperature is higher.

Skin temperature is highly correlated to the ambient air temperature and to the amount of clothing worn. When training outdoors in winter conditions, it’s not unusual to have a Heat Strain Score of zero, even if core temp is elevated. This is because the body is not working hard to dissipate heat.

While a long workout in the heat may result in a score of several thousand, most users will find that their highest daily scores occur when sick with a fever. A daily Heat Strain Score of over 10,000 is not atypical during a strong fever, and accurately represents the extreme stresses on the body (and helps to quantify the reason why exercise avoidance is recommended while experiencing a fever).

Applications for training

The Heat Strain Score is valuable for analysing training and race performance. It adds another dimension to core body temp to explain the condition and physiology of the athlete.

In the CORE app, you will find a Heat Strain Score calculated for all prior workouts recorded with CORE. Examining the Heat Strain Score in various races and training sessions will likely reveal patterns and thresholds where athletes started to experience performance decline. In particular, look at long endurance efforts in the heat, races in any conditions, and longer high-intensity efforts.

Notice if there is a threshold Heat Strain Score associated with performance decline. Also note if there was an ambient air temperature that was associated with little or no Heat Strain Score, even during a race where core temp was quite elevated. More tips and training advice coming soon!

What is 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.

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