J. Guilliams, L. Eagleman, M. Schleh, C.L. Dumke FACSM

University of Montana Dept. of Health and Human Performance – Missoula, MT

INTRODUCTION: Occupational athletes such as wildland firefighters (WLFF) use sports drinks to retain fluid, and provide electrolytes and carbohydrates during long duration exercise in the heat. The optimal concentrations of key ingredients for maximal fluid retention and alteration of fuel utilization is unknown. PURPOSE: The purpose of this study is to compare two commercially available beverages, DD (60.9 mM Na+, 3.4% CHO ) vs G (18.4 mM Na+, 5.9% CHO) on their ability to affect fat and carbohydrate metabolism during submaximal exercise in the heat. METHODS: Ten aerobically fit males (22.5± 3.9 yrs, 82.2± 10.1 kg, 53.9± 5.9 ml•kg-1•min-1 VO2 max) completed two 90-minute heat stress trials (39º C, 30% RH) walking at 50% VO2 max followed by a 30-minute rest period. Respiratory gases were collected mid (45 min) and post-exercise (90 min). At 45 minutes, subjects consumed either G or DD with volume equivalent to 150% of the weight lost. Subjects wore a standard WLFF Nomex uniform. Blood glucose was measured pre- and post-exercise, and post-trial. Data was analyzed using analysis of variance (ANOVA). RESULTS: Ventilation (VE) did not differ between G and DD (72.1 ± 8.4 vs. 69.4 ± 7.5 L•min-1; p=0.5). Oxygen consumption (VO2) was not different between trials (2.4 ± 0.1 vs. 2.4 ± 0.2 L·min-1; p=0.3). Similarly, carbohydrate oxidation was not significantly different between the beverages (2.1 ± 0.2 vs. 1.8 ± 0.2 g·min-1; p=0.2) for G vs. DD respectively. However, significant differences in fat oxidation and respiratory exchange ratio (RER) were found (0.38 ± 0.03 vs. 0.47 ± 0.05 g·min-1; p=0.049, and 0.89 ± 0.02 vs. 0.87 ± 0.01; p=0.04) in GG vs. DD respectively. Additionally, blood glucose was significantly greater post-trial in G vs. DD (116.0 ± 5.7 vs. 103.1 ± 3.9 mg·dL-1; p=0.01). CONCLUSION: Following the consumption of a bolus of G (5.9% CHO) resulted in increased RER and reduced fat oxidation compared to a bolus of DD (3.4% CHO). Similarly, blood glucose was greater following ingestion of G. These data may prove critical for WLFF during extended periods of work in the field.

Supported by U.S. Forest Service

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