Temperature Monitoring in Sport: Methods, Insights, and Practical Applications

Athletes and coaches are increasingly interested in heat strain monitoring as a tool to better understand the body’s response to heat stress, optimize performance, and improve heat training strategies.  

While many people associate thermal monitoring with tracking a single number for the body’s core temperature, the reality is more complex. To get meaningful insights, it is important to understand both the strengths and limitations of different thermal monitoring methods and how they can support real-world training decisions. 

Core Temperature Monitoring 

When discussing thermal monitoring, people often refer to the body's "core temperature" as if it were a single fixed value. In reality, temperature varies between different tissues and organs, and measurements taken at different locations can produce different values at the same moment. 

Methods such as ingestible sensors, rectal probes, and non-invasive technologies each provide useful information, but no measurement approach is without limitations.  

Non-Continuous Temperature Measurements 

Most commercially available thermometers (e.g. ear, axillary, oral, forehead, rectal) provide a single reading at a specific moment in time. While useful for quick assessments, they offer only a snapshot of a continuously changing physiological process. During exercise, body temperature can change rapidly, making it difficult to understand the full picture from spot-checks alone. 

Ingestible capsules 

Ingestible temperature capsules, or e-pills, are widely used in sports science and research. 

After being swallowed, the pill measures temperature from within the gastrointestinal tract and transmits data wirelessly. This allows continuous monitoring during exercise and has made e-pills a valuable tool for researchers and elite sport practitioners. 

However, the largest challenge for practitioners is that they are single-use devices, require dedicated hardware, and can only be used while the pill remains in the body, resulting in relatively high operating costs. 

Because temperature varies throughout the body, measurements can also be affected by the pill's location within the gastrointestinal tract, as well as factors such as fluid intake and gastrointestinal movement. 

Invasive Probes 

Invasive probes, including rectal and esophageal thermometers, are another established method of monitoring core temperature. 

Rectal thermometry remains an important clinical tool and is widely used by medical professionals when assessing and monitoring suspected heat stroke. 

In sports settings, however, invasive probes are generally impractical for routine day-to-day use due to their invasive nature. Their use is therefore typically limited to clinical applications, laboratory testing, and research studies. 

As with all temperature measurement methods, probe measurements are influenced by factors such as measurement location, placement, physiology, and testing protocols. 

 

The CORE Approach 

For athletes and coaches, the most important consideration is often whether a method can be used in real-life settings, and whether it provides practical, repeatable insights that can help guide training, monitor heat strain, and track adaptation over time. CORE was developed as a non-invasive and continuous tool to support these needs in training and competition. 

The CORE sensor continuously measures skin temperature and heat flux. Skin temperature reflects the body’s interaction with the environment, while heat flux indicates whether the body is gaining or losing heat. Together, they provide important information regarding the body’s thermal state. These measurements are combined with heart rate data, reflecting cardiovascular strain as well as changes in metabolic heat production during exercise. Using these physiological inputs, a proprietary machine-learning algorithm estimates core temperature in real time. 

The algorithm was developed using large datasets collected across a wide range of participants, environmental conditions, exercise intensities, and daily-life scenarios. These datasets include reference measurements from established invasive temperature measurement methods, including ingestible capsules and rectal probes, which are used to train and continuously improve the model. 

While CORE readings may be influenced by individual physiology, sensor placement and mounting, and environmental conditions, it allows athletes to access continuous temperature monitoring without the inconvenience and logistical challenges associated with invasive methods. 

Beyond Core Temperature 

For athletes, a single core temperature value rarely tells the whole story. 

In addition to estimating core temperature, CORE directly measures skin temperature, an important indicator of heat strain. CORE combines core and skin temperature data into it’s Heat Strain Index, which informs you how hard your thermoregulatory system is working to cool itself. 

CORE also translates this temperature data into athlete-focused metrics and guidance, for example through the Heat Training Load and Heat Adaptation Score. Rather than simply reporting temperature, these insights help athletes and coaches understand how the body is responding to heat and how heat adaptation develops over time. 

 

Finding the Right Tool for the Right Purpose 

Every thermal monitoring method has strengths and limitations. 

Spot measurements can provide quick assessments. E-pills and internal probes are commonly used in research and clinical environments. Rectal thermometry continues to play an important role in the clinical assessment of heat stroke. 

CORE is designed with a different goal: providing athletes and coaches with a practical, non-invasive, continuous monitoring solution that can be used regularly in training and competition, while also delivering additional context through skin temperature, heat strain metrics, and heat adaptation insights.