EFFECTS OF FLAME RESISTANT SYNTHETIC MATERIAL ON MEASURES OF HYDRATION

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

SYNTHETIC UNDERSHIRTS IMPACT ON THE METABOLIC DEMAND WHILE WEARING WILDLAND FIREFIGHTER GARMENTS

Wildland Firefighters benefit from additional fire resistant clothing; however this may increase metabolic demand. PURPOSE: This study evaluates the effects of a flame resistant synthetic base undershirt on the metabolic demand while exercising in a hot environment. METHODS: Ten recreationally active male subjects (age: 25 ± 6.1, 55.0 ± 7.1ml·kg-1·min-1 VO2max, 11.1 ± 5.3 %fat) completed two walking trials clothed in either a Cotton (C) or Synthetic (S) undershirt. Additionally subjects were equipped with Forest Service issued Person Protective Equipment consisting of a 35 lb pack, Nomex shirt, Nomex pants, gloves, and hard hat. Trials consisted of 180 minutes of walking (2.5 mph, 4% grade) in a climate-controlled chamber (35oC and 40% relative humidity). Each 180 minute trial was divided into three 50 minute exercise bouts followed by 10 minute seated rest. Expired gases were collected at time intervals 5, 40, 100, 160 minutes during exercise to determine oxygen consumption (VO2) and Respiratory Exchange Ratio (RER). Heart Rate (HR), Rate of Perceived Exertion (RPE) Core temperature (Tc), and skin temperature (Tsk) were collected every 10 minutes. Repeated measures of ANOVA’s were performed using SPSS 22.0. RESULTS: HR showed an increase over time (p\u3c0.001), but did not have a significant difference between S and C (p=0.27). RPE displayed significant effects in time (p=0.001) but no significant in trials (p=0.55). Tc and Tsk also increased over time (p\u3c0.001), but did not show a difference between the two under shirts (p=0.73). RER increased over time (p=0.01) but did not differ between trials (p=0.92). VO2 demonstrated a time x trial interaction (p=0.048), with S being greater than C by the end of the trial (18.2 ± 0.5 ml·kg-1·min-1 vs 17.7± 0.6 ml·kg-1·min-1). CONCLUSION: While the data does not show differences between the two shirts in HR, Tc, Tsk, and RPE, there was an increase in VO2 suggesting that a flame resistant synthetic undershirt elicited an increase in energy expenditure