Application of a skin calorimeter to study local heat loss during exercise

Abstract

The evaluation of local heat loss during exercise provides relevant information on muscle activity and thermoregulatory mechanisms. In this study, a custom-designed skin calorimeter was used to measure heat loss over active muscles during moderate exercise. The device incorporates a thermopile and a thermostat, enabling precise thermal control and reliable heat flux estimation through a previously validated thermal model. We propose a method to characterize muscle's thermal response using a personalized transfer function (TF) that relates the mechanical power developed by the subject to the localized heat flux. Experiments were conducted on a healthy male subject, performing exercise at 80 W on a stepper. The heat flux was measured at the rectus femoris, under different thermostat temperatures. The resulting TFs showed consistent dynamic behavior, with sensitivities and time constants that support quantification of the muscle's thermal response. These findings support the feasibility of using skin calorimetry to non-invasively model muscle heat dynamics during exercise. This approach establishes a solid basis for future clinical applications.