Prediction of mean skin temperature for use as a heat strain scale by introducing an equation for sweating efficiency

The present paper made the heat balance equation (HBE) for nude or minimally clad subjects a linear function of mean skin temperature (t(sk)) by applying new equations for sweating efficiency (η(sw)) and thermoregulatory sweat rate (S(wR)). As the solution of the HBE, the equation predicting t(sk) was derived and used for a heat strain scale of subjects. The η(sw) was proportional to the reciprocal of S(w)/E(max) (S(w), sweat rate; E(max) maximum evaporative capacity) and the S(wR) was proportional to t(sk) with a parameter of the sweating capacity of the subject. The errors of predicted t(sk) from observations due to the approximation of η(sw) were examined based on experimental data conducted on eight young male subjects. The value of errors of t(sk) was -0.10 ± 0.42 °C (mean ± sample standard deviation (SSD)). We aim to apply the predicted t(sk) of a subject at a level of sweating capacity as a heat strain scale of a function of four environmental factors (dry- and wet-bulb temperatures, radiation, and air velocity) and three human factors (metabolic rate, sweating capacity, and clothing (≤0.2clo)).