EXOGENOUS FLUID DELIVERY SCHEDULE AND COMPOSITION ON FLUID BALANCE, PHYSIOLOGIC STRAIN, AND SUBSTRATE USE IN THE HEAT

Introduction: Wildfire suppression is characterized by high total energy expenditures and water turnover rates. Hydration position stands outline hourly fluid intake rates. However, dose interval remains ambiguous. We aimed to determine the effects of micro- and bolus-dosing water (MW, BW) or carbohydrate-electrolyte (MCE, BCE) solutions on fluid balance, heat stress, and carbohydrate oxidation during extended thermal exercise. Methods: Males (n=12), in a repeated measures cross-over design, completed 4, 120-minute treadmill trials (1.3 m.s-1, 5% grade, 33°C, 30%RH) wearing a USFS uniform and 15kg pack. Fluid delivery approximated losses calculated from a pre-experiment familiarization trial, providing 22 doses.h-1 or 1 dose.h-1 (46±11,1005±245 ml.dose-1). Body weight (pre-, post-exercise) and urine volume (pre-, during, post-exercise) were recorded. Heart rate, rectal temperature, skin temperature, and steady state expired air samples were recorded throughout exercise. Differences were determined via repeated measures ANOVA’s with statistical significance set at p\u3c0.05. Results: Total body weight loss (n=11, -0.6±0.3 kg, p\u3e0.05) and cumulative urine output (n=11, 677±440 ml, p\u3e0.05) were not different across trials. Exercise sweat rate was lower in the MCE trial than the BCE, BW, and MW trials (n=11, 0.86±0.22, 0.93±0.21, 0.91±0.23, 0.89±0.22 ml, respectively, p\u3c0.05). PSI was lower at minute 60 than 120 (3.6±0.7, 4.5±0.9, p\u3c0.05), with no differences across trials. Carbohydrate oxidation was higher in the CE trials than the W trials (1.5±0.3, 0.8±0.2, g.min-1, p\u3c0.05), with no differences between identical composition dosing styles. Conclusions: Varied fluid delivery schedules of equal volume did not affect fluid balance, PSI, and carbohydrate oxidation during extended thermal work