Precooling via immersion in CO₂-enriched water at 25°C decreased core body temperature but did not improve 10-km cycling time trial in the heat

ABSTRACT

This study compared the effects of precooling via whole-body immersion in 25°C CO₂-enriched water (CO₂WI), 25°C unenriched water (WI) or no cooling (CON) on 10-km cycling time trial (TT) performance. After 30 min of precooling (CO₂WI, 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 CO₂WI (−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 CO₂WI versus CON was observed at 15^th min of exercise (p = 0.050). Skin temperature was lower in CO₂WI and WI than in CON during the exercise (p < 0.001 to 0.031). Only CO₂WI (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 CO₂WI and WI versus CON only during precooling (p < 0.001 to 0.041). NIRS-derived blood volume was significantly lower in CO₂WI 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 CO₂WI maybe more effective than WI for enhanced core body cooling and minimized sweat losses.

KEYWORDS:

• Endurance
• thermoregulation
• carbonated water immersion
• CO₂ bathing
• artificial carbonic acid water
• near-infrared spectroscopy

Acknowledgments

The authors would like to thank the participants for their involvement in the study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contribution statement

HCC, MI, KMC, and MC conceived and designed the experiments; LA, ZYL, CKM, and HCC performed the experiments; HCC and ZYL analyzed and interpreted the data; LA, HCC, and MI wrote the first draft. All authors critically reviewed and approved the manuscript.

Additional information

Funding

This work was supported by the Runme Shaw Sport Science Research Grant under Grant [RSSSRG/FY22/01Physiology].