Ice slurry ingestion before and during exercise inhibit the increase in core and deep-forehead temperatures in the second half of the exercise in a hot environment.

Many studies have reported that pre-exercise ice slurry ingestion improves exercise performance; however, it may increase the risk of developing heat stroke. Some studies have suggested that pre-exercise ice slurry ingestion accelerates the core temperature increase that occurs during exercise. Therefore, this study aimed to investigate whether the ingestion of ice slurry before and during exercise can inhibit this acceleration. Moreover, we measured the deep-forehead temperature (Tdeep head) to determine whether ice slurry ingestion before and during exercise can maintain this reduction in brain temperature. Eleven male participants at room temperature (24 °C, 50% relative humidity [RH]) ingested 7.5 g/kg of ice slurry or a thermoneutral sports drink within 30 min. They then exercised for approximately 60 min at 50% of the maximal oxygen uptake in a hot environment (34 °C, 50% RH) while ingesting 1.25 g/kg of ice slurry or a thermoneutral sports drink every 10 min. Rectal temperature (Tre), Tdeep head, forehead skin temperature, mean skin temperature, heart rate, nude body mass, and urine specific gravity were measured as physiological indices. The rating of perceived exertion, thermal sensation, and thermal comfort were measured at 5-min intervals throughout the experiment. The Tre and Tdeep head during the second half of the exercise session were significantly reduced after ingestion of the ice slurry before and during exercise (p < 0.05). In addition, the rate of increase in Tre and Tdeephead slowed during the second half of the exercise session after the ingestion of the ice slurry before and during exercise (p < 0.05). These results indicate that the increases in Tre and Tdeep head, reflecting brain temperature in the second half of the exercise session, were significantly inhibited by ice slurry ingestion before and during exercise.