Infrared thermography is once again emerging as a non-invasive and accurate method to analyze exercise physiology.

A research team from the Beijing Sport University evaluated 23 physically active individuals to determine whether there is a relationship between ventilatory thresholds and skin temperature variations recorded through infrared thermography.

Until now, these thresholds, essential for defining training zones, could only be determined through gas analyzers or blood lactate measurements, which are costly and, in many cases, invasive. This study presents a simple, visual, and contact-free alternative.

Thermography as a tool for assessing exercise effort

During an incremental cycling test, researchers simultaneously measured oxygen uptake (VO₂), heart rate (HR), power output (PO), and the average skin temperature (aTsk) of the thigh. Using a dynamic programming algorithm in Python, they identified two thermal inflection points in the temperature curve:

• TSKT1: the moment when skin temperature begins to drop, indicating the onset of higher metabolic effort.
• TSKT2: the point when temperature stops decreasing or starts to rise, marking the transition toward fatigue or severe effort.

Results: Correlation Between Skin Temperature and Ventilatory Thresholds

The results revealed a strong agreement between TSKT2 and the second ventilatory threshold (VT₂), with correlation coefficients above r = 0.77 for absolute oxygen uptake (VO₂ab) and power output (PO), and a high reliability (ICC > 0.75).

These findings demonstrate that cutaneous thermal changes closely reflect metabolic responses during exercise.

In practical terms, skin temperature can serve as a direct, non-invasive indicator of ventilatory thresholds and overall physiological effort.

Practical Applications of Thermography in Sports

Using infrared thermography to evaluate exercise intensity offers several advantages:

• Completely non-invasive and contact-free method.
• Allows continuous monitoring during exercise.
• Enables comparison between athletes, sessions, or body regions.
• Provides real-time feedback on blood flow redistribution and metabolic activation.

These features make thermography a promising tool for training load control, fatigue prevention, and performance optimization.

Conclusion

This study confirms that skin temperature is a direct reflection of metabolic effort and is strongly related to the most relevant physiological variables in exercise science.

Infrared thermography thus emerges as a scientifically validated, precise, and visual tool for estimating ventilatory thresholds and monitoring athletic performance without invasive or expensive procedures.

In short, it is a powerful innovation in exercise physiology, a technology capable of translating body heat into measurable physiological information.