The Effect of Water Dousing on Heat Strain and Performance During Endurance Running in the Heat

Abstract

Objectives: Assess the effect of water dousing on heat strain and performance during self- and fixed-paced exercise in the heat. Design: Crossover, block-randomized controlled trial. Methods: Thirteen trained runners completed a 10-km time trial (TT) and 60-minute fixed-pace run (60% velocity of ) in a 30.4 °C, 47.4% relative humidity environment using either water dousing (DOUSE) or no dousing (CON). Results: Ten-kilometer TT performance was faster in DOUSE compared to CON (44:11 [40:48, 47:34] vs 44:38 [41:21, 47:56] min:s; P = .033). Change in core temperature (Tc) was not different between groups during the TT (+0.02 [−0.04, 0.07] °C in DOUSE; P = .853) or fixed-pace run (+0.02 [−0.15, 0.18] °C; P = .848). Change in mean skin temperature was lower in DOUSE during the TT (−1.80 [−2.15, −1.46] °C; P < .001) and fixed-pace run (−1.38 [−1.81, −0.96] °C; P < .001). Heart rate was lower for DOUSE during the fixed-pace run (−3.5 [−6.8, −0.2] beats/min; P = .041) but not during the TT (−0.2 [−2.5, 2.1] beats/min; P = .853). Thermal sensation was lower for DOUSE during the TT (−49.3 [−72.1, −26.1] mm; P < .001) and fixed-pace run (−44.7 [−59.7, −29.6] mm; P < .001). Rating of perceived exertion was not different between groups for the TT (−0.2 [−0.7, 0.3]; P = .390) or fixed-pace run (−0.2 [−0.8, 0.4]; P = .480). Sweat rate was lower for DOUSE for the TT (−0.37 [−0.53, −0.22] L/h; P < .001) and fixed-pace run (−0.37 [−0.48, −0.26] L/h; P < .001). Conclusion: Water dousing improves 10-km TT performance in the heat but does not affect Tc. The positive change in thermal perception (via lower skin temperature) during the TT likely drives this benefit.