Validation and adjustment of the mathematical prediction model for human sweat rate responses to outdoor environmental conditions

Based on indoor laboratory studies, a mathematical model to predict sweat loss response was suggested as follows: (Formula Present)Under outdoor conditions this model was over estimating sweat loss response in shaded (low solar radiation) environments, and underestimating the response when solar radiation was high (open field areas). The present study was conducted in order to adjust the model to be applicable under outdoor environmental conditions. Four groups of fit acclimated subjects participated in the study. They were exposed to three climatic conditions (30°, 65% rh; 31°C, 40% rh; and 40°C, 20% rh) and three levels of metabolic rate (100, 300 and 450W) in shaded and sunny areas while wearing shorts, cotton fatigues (BDUs) or protective garments. The original predictive equation for sweat loss was adjusted for the outdoor conditions by evaluating separately the radiative heat exchange, short-wave absorption in the body and long-wave emission from the body to the atmosphere and integrating them in the required evaporation component (E_req) of the model, as follows: (formula present)where SL is solar radiation (W·m⁻²), M_{e. th} is the Stephan Boltzman constant, and l_T is the effective clothing insulation coefficient. This adjustment revealed a high correlation between the measured and expected values of sweat loss (r = 0·99, p < 0·0001).