Development of Wearable Multimodal Sensor Probe for Measurement of Core Body Temperature, Heart Rate, and Sweat Rate

Global warming and frequent heatwaves make the prevention of heat-related illness an urgent issue. To avoid dangerous heat stress, monitoring core body temperature, heart rate, and sweat loss is essential. Conventional methods rely on several separate sensors, which reduces practicality in daily life or field use. This study introduces a compact, wearable multimodal sensor probe that can simultaneously measure core body temperature, electrocardiogram (ECG), heart rate, and sweat rate. The device uses a heat flux-based unit to track both core body temperature and cardiac signals, while a computational model estimates sweat loss. Validation experiments were conducted with ten healthy men during cycling exercise in a controlled environment. The prototype achieved a root mean square error of 0.087°C for core temperature and 131 g for total sweat loss, surpassing previous approaches. During exercise and recovery, values were slightly overestimated, likely due to increased sweating and skin blood flow affecting heat transfer. Despite these limits, the device provides a practical way to monitor multiple physiological signals in real time under heat stress. It shows promise for use in occupational, athletic, and everyday settings to help prevent heat illness.