Abstract
Background and Objectives: Hyperthermia significantly limits endurance performance in hot environments. To enhance heat loss and optimize athletic performance, pre-cooling interventions can be employed to accelerate body cooling. Therefore, the aim of this study was to evaluate the effects of an internal pre-cooling intervention combined with external pre-cooling or hydrogen-rich water on endurance performance in the heat. Materials and Methods: In a double-blind crossover with counterbalanced trials, all participants underwent a shuttle run test after 30 min under the following conditions: (1) hydrogen-rich cold water ingestion (HRCW); (2) cold water ingestion and external pre-cooling (IEPC); and (3) cold-water ingestion (control). Maximal aerobic speed (MAS), number of shuttle run repetitions, dehydration, temperature, heart rate (HR), rate of perceived exertion (RPE), blood lactate, and feeling scale (FS) were measured during the 20 m shuttle run test. Results: Our results revealed a significant variation in dehydration, MAS, number of shuttle run repetitions, blood lactate, RPE, and FS (p = [0.001-0.036]); additionally, a significant group × time interaction was found for body temperature (p = 0.021). Post hoc tests revealed a significant change for MAS (HRCW: p < 0.001), number of shuttle run repetitions (HRCW: p < 0.001), dehydration (HRCW: p= 0.009; IEPC: p = 0.008), blood lactate (HRCW: p < 0.001; IEPC: p < 0.001), RPE (HRCW: p = 0.05; IEPC: p = 0.004), and FS (HRCW: p = 0.05; IEPC: p = 0.004), as well as a significant decrease in body temperature (IEPC: p < 0.001; HRCW: p = 0.028) compared to the control condition after the test. However, no significant differences were reported in HR among the different conditions. Conclusions: In conclusion, findings from this study suggest that ingesting hydrogen-rich cold water effectively mitigates the effects of heat stress, thereby improving endurance performance, enhancing mood, and reducing ratings of perceived exertion.