A simplified approach to describe the mean skin temperature variations during prolonged running exercise

Skin blood flow and skin temperature play a fundamental role in the thermoregulatory processes and are expected to largely change in response to a prolonged running exercise. The skin temperature changes have been documented in the literature, mainly through infrared thermographic measurements performed before, after, and, in a limited number of studies, during the exercise. After an initial reduction probably ascribed to skin vasoconstriction, the further skin temperature modifications with time, measured in reference papers during a steady and prolonged run, do not show a common behaviour, probably due to different exercise intensities and environmental conditions reported in these studies. This research aimed to develop a simplified method for describing the skin temperature changes during running exercise through the theoretical solutions of the dynamic energy balance of the human body in the early and late time periods, i.e., close to the onset and the end of exercise. These two asymptotic solutions for the skin temperature, having a largely dissimilar trend, collide at a time instant likely associated with the switch from skin vasoconstriction to vasodilation. Examples of application of the proposed method, based on the intersection of asymptotes, were provided. It was also demonstrated its capability to interpret the experimental skin temperature variations with time for constant-load running exercises reported in the literature under different levels of exercise intensity and environmental conditions.