T. Stenersen, J. Center, K. Heinze, C. Palmer, J. Domitrovich, C. Dumke FACSM

University of Montana, Missoula, MT

Heat related illness (HRI) is of major concern within heat related occupations. The addition of personal protective equipment (PPE) exacerbates the issue of HRI due to uncompensable heat stress. The inability to offload heat due to PPE, from shirts, pants, and boots, has been investigated in the past and shown to effect performance along with increased risk of HRI. While previous research has focused on different types of PPE, there is little research involving the WLFF helmet. PURPOSE: To investigate factors of heat stress with and without a standard issue WLFF helmet. METHODS: Eleven male subjects (age = 25.18±4.9 yrs) were recruited with a VO2>40 ml/kg/min and ≤65 ml/kg/min (VO2max= 54.16±5.5 ml/kg/min). Subjects were required to finish a 90-minute exercise protocol in a heat chamber (35˚C and 30% RH), with Nomex shirt, pants, cotton t-shirt, and either with or without a helmet. A randomized crossover design was implemented; with a minimum two week washout period. Skin blood flow to the head and neck (SBFh; SBFn), head heat (HH), CT, skin temperature on chest and neck (STc; STn), HR, PSI, RPE, perceived head heat (PHH) and sweat rate were recorded during trials. A 2x3 ANOVA was used to analyze SBF, and 2x4 ANOVA was used to analyze HH, CT, ST, HR, PSI, RPE, and PHH. One-way ANOVA was used to analyze sweat rate. RESULTS: Nine of the 11 subjects were able to finish the 90 minute exercise trial. The HH, SBFh, and PHH (36.41±0.76˚C w/helmet v. 35.22±0.98˚C w/out helmet; 211.93±86.84 w/helmet v. 185.51±73.34 w/out helmet; 10.07±3.25 w/helmet v. 8.52±2.65 w/out helmet; respectively) were all significant (p<0.05) with a main effect between trials. HR, PSI, CT, and STcdemonstrated main effects of time (p<0.05), but were not different between trials. Sweat rate was not significant among trials (2.09±0.44 L/h w/helmet vs. 1.85±0.44 L/h w/out helmet). CONCLUSION: These data (HH, SBFh, and PHH) suggest that the current WLFF helmet design causes excess heat accumulation and resultant redirection of blood flow to the head. While some physiological factors (CT, HR, ST, PSI, and sweat rate) did not reach significance between trials; trends existed for PSI and RPE. The design of the WLFF helmet lacks ventilation, which from these data, may result in metabolic alterations, and perceived discomfort.

Funded by the USFS (14-CR-11138200-009)

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