Metabolic heat flux density (M) in the human biometeorological models: Can M be parameterized based on heart rate estimated by smart devices?

In this study, we focus on the calculation methods of human metabolic heat flux density (M) and on the applications of these methods in human thermal load models. Special attention was paid to the method that calculates M based on the heart rate (HR). A new M – HR based formula is presented. The connection was determined by measuring the average movement speed (V) and heart rate at the same time and then calculating M from V. The average V was determined by using a stopwatch. The average HR value was measured by using the Applewatch smart watch. The M(V) relationships are taken from the literature. Two persons performed the measurements in Martonvásár (a town close to Budapest), Budapest and Szombathely: a younger woman and an older man. The main lesson of our research is that M – HR based parametrization is individual-specific, despite the fact that the M – HR relationship can be characterized by a general function, which initially increases exponentially and then enters a saturation phase. This type of research will be widespread, given that we are living in the age of smart tools.