PHYSIOLOGICAL STRAIN BASED ON CRITICAL WBGT AND METABOLIC RATE

Abstract

Increased core temperature (Tre), skin temperature (Tsk) and heart rate (HR) are physiological indicators of heat strain. Heat stress is dependent on environmental conditions, metabolic raet, and clothing. PURPOSE The purpose of this study was to determine which of these variables of heat stress affect physiological markers of heat strain in certain types of protective clothing. METHODS Thirteen heat-acclimated participants (4F, 9M) walked at 3 metabolic rates (80, 160, & 240 W/m2) in five different clothing ensembles (cotton work clothes, cotton coveralls, Tyvek 1424, NexGen, & Tyvek QC). Trials began under environmental conditions set at 34 ° C, 50% rh. Once the participants reached physiological steady state, temperature was increased incrementally until the participant could no longer maintain thermal equilibrium. This was designated as critical WBGT. Multiple linear regression was performed with Tre, Tsk and HR as the dependent variables. RESULTS Clothing was not a significant predictor of any of the dependent variables (p > 0.05). For HR, critical WBGT was a significant predictor but accounted for only 9% of the variance (p < 0.05). Both metabolic rate and critical WBGT were significant predictors of Tsk accounting for 25% of the variance with critical WBGT alone accounting for 19.5% of the variance (p < 0.05). Both metabolic rate and critical WBGT were significant predictors of Tre accounting for 29.5% of the variance. Metabolic rate alone accounted for 28% of the variance in Tre (p < 0.05). CONCLUSION HR and Tsk can be predicted from critical WBGT. Increased Tre is primarily dependent on metabolic rate.