Change In Physiological Strain And Cognitive Processing Following Electrolyte And Carbohydrate Supplementation

Abstract

PURPOSE: The purpose of this study was to examine the effects of 3 different fluid conditions on hydration, physiological strain index (PSI), and cognitive processing speed during and following a simulated wildland firefighter (WLFF) ingress hike. METHODS: 7 subjects (27.4±4yrs, 5M/2F) performed 3 visits of 2hrs of treadmill walking at 3mph/7% grade in an environmental chamber set to 33°C/10% relative humidity. In random order, subjects consumed either water (W), water+electrolyte (GZ), or water+electrolyte+sugar (G) at each visit. Throughout exercise (EX), subjects wore fire-retardant attire, carried a 50lb pack, and drank ad libitum to mimic WLFF conditions. Pre and post EX, body mass (BM), fluid consumption, and plasma osmolality (pOsm) were measured. PSI, an calculated index of cardiovascular (CV) and thermal strain, and core temperature (TC) were recorded every 15mins during EX. Plasma glucose (GLU) was measured every 30mins. Cognitive processing speed, measured via the Stroop Color and Word Test (SCWT), was measured post EX and compared to baseline (BL) values. RESULTS: There were no significant differences between fluid conditions (W, GZ, and G) for BM (Δ 0.6±0.2, 0.9±0.3, and 0.8±0.2 Kg), fluid consumption (1.9±0.3, 2.2±0.2, and 1.9±0.3 L), pOsm (Δ 1.2±5.1, 9.5±5.4, and 8.1±2.1 mmol/L), peak PSI (7.6 ± 0.6, 7.8 ± 0.5, and 8.6 ± 0.7) and peak TC (38.8 ± 0.2, 38.9 ± 0.2, and 39.1±0.2 °C). Compared to W and GZ, GLU significantly increased in the G condition (107±14, 107±13, and 113±11 mg/dL at 60, 90, and 120mins, P <0.05). Compared to BL, SCWT performance significantly decreased in all conditions (204.2±21, 213±24, and 222±21 ms, P <0.05). CONCLUSION: Fluid condition had no effect on hydration status or physiological strain. Following EX, there was a similar decrease in SCWT in all fluid conditions, indicating a decreased ability to inhibit cognitive interference. Additionally, PSI was higher than previously reported, suggesting that the ingress hike may lead to dangerously high CV and thermal strain in WLFFs. PSI should be monitored (HR and TC) during ingress hikes by medical staff or supervisors, especially when conditions yield high ambient temperatures. This could aid in reducing the amount of WLFFs that succumb to heat related illness each year. Grant Funding: The project was funded by the US Forest Service.