Improved Evaluation And Application Of Physiological Equivalent Temperature For Assessing External Heat Load In Marathon Runners

Background Recently,outdoor sports events such as the urban marathon have been greatly developed in China,but the risk of heat-related illness for marathon participants are increasing due to global warming and excessive urbanization.Thermal comfort is one of thermal response indicators that can monitor the external heat load of sports participants in indoor thermal environments and predict the incidence of heat-related illness.However,its applicability in outdoor environments has been rarely studied.The Munich Energy Balance Model for Individuals(MEMI)is a mathematical heat comfort model based on the human energy balance equation.MEMI can derive Physiological Equivalent Temperature(PET)under certain conditions,which is a thermal comfort index applicable to outdoor environments.This parameter simultaneously considers temperature,humidity,radiation,wind,and the metabolic rate of sports participants,making it superior to similar indicators in terms of calculation principles.However,MEMI is a model established based on low-tomoderate intensity activity levels.Objective Computing the improved Physiological Equivalent Temperature(PET~*)index and investigate the relationship between PET,PET~* and Wet Bulb Globe Temperature(WBGT)and the incidence of heat stroke cases in selected marathon races.Method By modifying the convection term,evaporation term,metabolic term and radiation term in MEMI model,new thermal comfort index PET~* was calculated.By using the number of heat stroke cases,total number of participants,and EC meteorological reanalysis data during the Yangzhou Jianzhen Half Marathon from 2010 to 2015,a PET~* was calculated and compared with PET and the other heat load parameter Wet Bulb Globe Temperature(WBGT)recommended by the International Olympic Committee.The simple linear regression model and Monte-Carlo algorithm are used to analyze their relationships with the incidence of heatstroke.Results(1)Compared with PET~*,PET overestimated the level of true thermal stress,and it was more sensitive to the change of air temperature and average radiation temperature,less sensitive to the change of humidity and wind;(2)Separately,the maximum and minimum number of heatstroke were 2.981/1 000 and 0.416/1 000.The maximum PET~*,PET and WBGT were 31.64℃,32.65℃ and 21.47℃,and the minimum PET~*,PET and WBGT were 21.22℃、25.64℃、12.85℃.PET~*,PET and WBGT had statistical significance on the incidence of heatstroke(P=0.009,P=0.024 and P=0.042),and the determination coefficients were 0.851,0.757 and 0.686,respectively;(3)The MC slope of PET~*,PET and WBGT for incidence were 0.209,0.191 and 0.230 respectively,and the MC simulation values of intercept were-3.770,-3.991 and-2.862 respectively.The MC 95%CI slope of PET~*,PET and WBGT are(0.207,0.215),(0.211,0.225)and(0.198,0.210)respectively,and 95%CI simulated values of the intercept are(-3.821,-3.605),(-4.729,-4.304)and(-2.275,-2.062)respectively.95%CI simulated values of R~2 are(0.57,0.91),(0.37,0.87)and(0.26,0.83)respectively.Conclusion The MEMI model is an applicable one for thermal comfort monitoring in outdoor environment.PET~* is a new indicator derived from the modification of the MEMI model,which is suitable in human body in sports.Compared with PET and WBGT,PET~* performs better in predicting the incidence of heat stroke in marathon,and it is a better indicator for thermal comfort monitoring in outdoor sports.This study covers shortcomings of previous studies,and it provides a new train of thoughts for the risk prediction and prevention in marathon.