Exertional Heat Strain After an Energy Drink and Caffeine-Equivalent Beverage in Wildland Firefighting Garments.

Abstract: Bartman, NE, Temple, JL, Hess, HW, Colburn, D, and Hostler, D. Exertional heat strain after an energy drink and caffeine-equivalent beverage in wildland firefighting garments. J Strength Cond Res XX(X): 000-000, 2025-Caffeine is widely consumed for its stimulant properties and potential ergogenic benefits. Wildland firefighters consume caffeine, but caffeinated energy drinks (ED) are discouraged. The purpose of this investigation was to assess physiologic and perceptual strain walking in wildland firefighting garments after consuming an ED or another equally caffeinated beverage (CAF). Twelve subjects {age (mean [95% confidence interval]): 27 (23-32) years, height: 173 (169-177) cm, mass: 76 (70-83) kg, V̇o2max: 43 (36-50) ml·kg-1·min-1} walked on a treadmill 90 min at 40-50% V̇o2max in 30° C, 80% RH conditions after consuming ED or CAF (200 mg caffeine). Significance was set at p ≤ 0.05. Peak core temperature (CAF: 39.1° C [38.9-39.3° C]; ED: 39.1° C [38.8-39.4° C], p = 0.94), physiologic strain index (CAF: 8.5 [7.9-9.2] score; ED: 8.5 [7.7-9.4] score, p = 0.87), and perceptual strain index (CAF: 7.9 [6.7-9.0] score; ED: 8.0 [6.8-9.1] score, p = 0.75) were not different between conditions. There were no differences in sweat rate (CAF: 18 [10-26] mL·min-1; ED: 19 [14-24] mL·min-1, p = 0.66), peak heart rate (CAF: 175 [167-184] b·min-1; ED: 177 [168-186] b·min-1, p = 0.86), perceived exertion (CAF: 8 [6-9] rating; ED: 8 [7-8] rating, p = 0.68), and fatigue (CAF: 7 [6-9] rating; ED: 7 [5-8] rating, p = 0.07). Consuming ED did not worsen physiologic or perceptual strain compared with consuming caffeine alone. For regular caffeine users, an ED may be an acceptable alternative caffeine source for wildland firefighters hiking in hot conditions.