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Unleash Your Potential with CORE’s Heat Strain Index

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Unleash Your Potential with CORE’s Heat Strain Index

The CORE Heat Strain Index is a cutting-edge tool that measures how hard your body is working to stay cool, delivering a real-time value from 0 (no heat strain) to around 10 (extremely high heat strain). Monitoring this index is crucial for preventing performance loss and adapting effectively to heat. To guide athletes in training and racing, CORE experts have developed four Heat Zones based on the Heat Strain Index.

CORE’s Heat Zones: A Practical Guide


It is important to note that the CORE sensor is not a medical device and is not intended to diagnose heat stroke or heat illness. Training or racing in Heat Zones 1-3 does not guarantee immunity from heat stroke or heat illness.

The Four Heat Zones

CORE’s Heat Zones provide insight into how heat stress affects your body:

  1. Heat Zone 1: Minimal heat strain, ideal for low-intensity training.
  2. Heat Zone 2: Moderate heat strain, suitable for moderate-intensity workouts.
  3. Heat Zone 3: High heat strain, best for heat adaptation training but should be avoided during competition.
  4. Heat Zone 4: Extreme heat strain, posing a high risk of heat-related illnesses.

These zones help athletes tailor their training and racing strategies to maximise performance while mitigating the risks associated with heat stress.

Training and Racing with Heat Zones

Implications of Each Heat Zone

Understanding the implications of each Heat Zone is essential for optimal training and racing. The following chart summarises the impact of different heat zones on performance and safety:

Heat Zone Description Training Implications Racing Implications
1 Minimal heat strain Safe for all training intensities Safe for racing
2 Moderate heat strain Good for moderate training Manageable for racing
3 High heat strain Ideal for heat adaptation training Best avoided during competition
4 Extreme heat strain Risky for training Dangerous for racing

For more detailed information on elevated heat strain, refer to the article "Heat Safety".

The Paradox of Heat Zone 3

The Crucial Role of Heat Zone 3

Heat Zone 3 plays a critical role in heat training. Although it is best avoided during competition due to increased heart rate and discomfort, it is ideal for heat adaptation. Regular training in this zone enhances the body’s ability to cope with heat, making it the most effective zone for heat training. While some adaptation occurs in Heat Zone 2, it takes longer to achieve and doesn’t maximise the body’s potential.

Individuality of Heat Zones

Personalising Your Heat Training

Heat tolerance and performance losses are highly individual. The exact thresholds for Heat Zones can vary widely among athletes due to factors like heat adaptation status, fitness level, body composition, and more. For instance, while some athletes may experience significant performance loss at a Heat Strain Index of 3.0–4.0, others might not see such effects until reaching a 5.0 or 6.0. It is crucial to identify your personal thresholds for effective heat training. For more tips, see the article "Heat Training Basics".

Introducing the CORE Sensor: Revolutionising Fitness Monitoring

The CORE Sensor offers continuous and precise tracking of core body temperature, enhancing performance and optimising training. This wearable device provides unparalleled insights into the body's response to physical exertion and environmental conditions.

Key Features of the CORE Sensor

  • Continuous and accurate core body temperature monitoring
  • Enhanced training adaptation through personalised cooling protocols
  • Compatibility with popular sports tech devices and training apps
  • Real-time data analysis for performance optimisation
  • Compact and waterproof design for versatile use in any activity
  • Long-lasting battery life with a rechargeable lithium-polymer battery

Moving Beyond Core Temperature

The Importance of Mean Body Temperature

While core temperature is a vital metric, it alone does not fully estimate thermal strain. Mean body temperature, a weighted average of core and skin temperatures, is a top indicator of heat strain. The CORE Sensor accurately estimates this value, providing a comprehensive picture of your thermal state and performance.

How Does It Work?

Advanced Sensor Technology

The CORE Sensor uses advanced technology to monitor core body temperature non-invasively. Worn on the chest, it captures accurate temperature readings unaffected by environmental influences. These readings, along with skin temperature measurements, are transmitted in real-time to the CORE app and compatible devices, offering immediate insights into heat strain and performance levels.

Making Informed Decisions

With real-time data on core body temperature and the Heat Strain Index, athletes can make informed decisions about pacing and cooling strategies. Understanding your body’s response to heat stress helps optimise performance and minimise the risks of overheating.

Seamless Integration and Convenience

The CORE Sensor integrates effortlessly with existing wearable technology and training apps via ANT+ and Bluetooth connectivity. Its compact, waterproof design ensures comfort and durability during any activity. The package includes essential accessories such as a USB magnetic charging cable, medical-grade adhesive patches, and clips for securing the sensor to a heart rate monitor strap.


The CORE Sensor is an invaluable tool for athletes seeking to understand and manage their body’s response to heat. By leveraging the Heat Strain Index and personalised heat zones, you can optimise your training, enhance performance, and stay safe in challenging conditions. Embrace the future of fitness monitoring with the CORE Sensor and unlock your full potential.

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