Article Title



Wildland firefighters (WLFFs) perform arduous labor in high-temperature environments. Protective gear worn by WLFFs may decrease ability to dissipate heat – putting fluid balance, performance, and safety at risk. PURPOSE: The purpose of this study was to investigate the effects of wearing a flame resistant synthetic material base layer shirt (underneath typical WLFF outerwear) on measures of hydration. METHODS: Recreationally active male subjects (n=10) had VO2 max and body fat percentage assessed prior to testing (25 ± 6.1 years, 11.1 ± 5.3% fat, 4.4 ± 0.6 L·min-1 VO2 max). Subjects completed two trials of the experimental procedure, each with a different base layer shirt material: either cotton or the flame resistant synthetic material, underneath standard issue WLFF personal protective gear and a 35lb pack. During each trial, subjects walked on a treadmill (2.5mph, 4% grade) in a climate chamber (35°C, 30%RH) for three 50-minute sessions with a 10-minute seated break in-between each session. Water was provided at 8 ml/kg/hr. After the three hours were complete, subjects removed their outer WLFF gear and sat for 30-minutes. Skin temperature (Tsk) and core temperature (Tc) were measured continuously. Hematocrit (Hct), urine specific gravity (USG), and body weight were measured before and after each trial. Repeated measures and one-way ANOVAs were used for statistical analysis. RESULTS: No significant differences were found in Tsk (p=0.086) and Tc (p=0.077) between the cotton and synthetic shirts. Weight loss (1.2 ± 0.2 kg, 1.3 ± 0.2 kg; p=0.53), percent dehydration (0.6 ± 0.1 %, 0.7 ± 0.1 %; p=0.54), and sweat rate (0.81 ± 0.03 L·min-1, 0.85 ± 0.04 L·min-1; p=0.40) were not different between the cotton and synthetic shirts respectively. There were no significant differences found on urine and blood markers between the two base layer shirts with USG (p=0.57) and Hct (p=0.48). Significant main effects for time were found with Hct (p=0.04). CONCLUSION: These results indicate that a flame resistant synthetic material did not compromise the hydration status of WLFFs while providing them additional protection from their work environment.

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