Abstract
This study compared the effects of precooling via whole-body immersion in 25°C CO(2)-enriched water (CO(2)WI), 25°C unenriched water (WI) or no cooling (CON) on 10-km cycling time trial (TT) performance. After 30 min of precooling (CO(2)WI, CON, WI) in a randomized, crossover manner, 11 male cyclists/triathletes completed 30-min submaximal cycling (65%VO(2peak)), followed by 10-km TT in the heat (35°C, 65% relative humidity). Average power output and performance time during TT were similar between conditions (p = 0.387 to 0.833). Decreases in core temperature (T(core)) were greater in CO(2)WI (-0.54 ± 0.25°C) than in CON (-0.32 ± 0.09°C) and WI (-0.29 ± 0.20°C, p = 0.011 to 0.022). Lower T(core) in CO(2)WI versus CON was observed at 15(th) min of exercise (p = 0.050). Skin temperature was lower in CO(2)WI and WI than in CON during the exercise (p < 0.001 to 0.031). Only CO(2)WI (1029 ± 305 mL) decreased whole-body sweat loss compared with CON (1304 ± 246 mL, p = 0.029). Muscle oxygenation by near-infrared spectroscopy (NIRS), thermal sensation, and thermal comfort were lower in CO(2)WI and WI versus CON only during precooling (p < 0.001 to 0.041). NIRS-derived blood volume was significantly lower in CO(2)WI and WI versus CON during exercise (p < 0.001 to 0.022). Heart rate (p = 0.998) and rating of perceived exertion (p = 0.924) did not differ between conditions throughout the experiment. These results suggested that CO(2)WI maybe more effective than WI for enhanced core body cooling and minimized sweat losses.