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.

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%VO2peak), 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 (Tcore) 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 Tcore in CO2WI versus CON was observed at 15th 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.

Hyperthermic effects of hand bathing: benefits of incorporating finger flexion-extension exercise.

[Purpose] The purpose of our study was to compare the effects of hand bathing using plain water and water supplemented with inorganic salt and carbonated gas and to assess the hyperthermic effects of performing finger flexion-extension exercise while bathing in water with carbonated gas and inorganic salt and without water. [Subjects and Methods] Sixteen healthy, young males were subjected to plain water bathing, CO2 bathing, kineto-CO2 bathing, or no bathing. CO2 bathing involved bathing in a solution of artificial bath additives including inorganic salts and carbon dioxide. Partial bathing of the hand was implemented for 20 minutes at 41 °C. The concentration of carbonic gas was set at 33 ppm. In the kineto-CO2 bathing condition, finger flexion-extension exercise was performed at 60 laps per minute in the same solution used in CO2 bathing. The control group engaged in the same exercise as those in the kineto-CO2 bathing group, but without bathing. [Results] A significant increase in deep-body temperature was observed in the CO2 bathing and kineto-CO2 bathing conditions compared with both the plain water bathing and control condition. [Conclusion] Significantly heightened hyperthermic effects were observed when finger flexion-extension exercise was performed during CO2 bathing.

Effects of Bathing With Artificial Bath Additive Including Inorganic Salts and Carbon Dioxide on Body Flexibility, Muscle Stiffness and Subjective Feeling of Bathing / 日本温泉気候物理医学会雑誌

 The effects of bathing in a solution of artificial bath additive including inorganic salts and carbon dioxide (CO2-bathing: 41°C, 10 minutes; the concentration of carbon dioxide was 160-180 ppm, and that of inorganic salts was about 64 ppm) on the cardiovascular system, body flexibility, muscle stiffness and the subjective feeling of bathing were compared with those of no bathing and plain water bathing in the healthy subjects.  The deep body temperature and skin blood flow increased after bathing, and the increases after CO2-bathing were significantly greater than those after plain water bathing. Body flexibility after CO2-bathing was similar to that of no bathing and plain water bathing.  Stiffness of the trapezius muscle was decreased at both 15 min and 30 min after CO2-bathing and plain water bathing, with no change in no bathing. The changes at 15 min after CO2-bathing and plain water bathing were statistically significant. Stiffness in the latissimus dorsi muscle decreased at both 15 min and 30 min after CO2-bathing and plain water bathing, with no change in no bathing. However, only these changes at 15 min and 30 min after CO2-bathing were statistically significant.  A large decrease in the stiffness of the trapezius muscle by its isometric contraction was observed during both CO2-bathing and plain water bathing, and the decrease after CO2-bathing was greater than that after plain water bathing. These changes did not reach statistical significance.  Improvements in subjective feeling of bathing were observed after both plain water bathing and CO2-bathing. Improvements after CO2-bathing in stiffness of muscle, ease of movements and mental relaxation were statistically greater than those after plain water bathing.  Compared with plain water bathing, CO2-bathing showed additional effects on muscle stiffness and subjective feeling of bathing. Further research is needed to confirm the effectiveness of the CO2-bathing alone and combined with isometric movements on muscle stiffness.