Abstract: BACKGROUND: Hydrogen, as an antioxidant, can reduce oxidative stress induced by strenuous exercise and achieve the effect of improving fatigue. Several studies have been reported on the potential effects of hydrogen-rich water or hydrogen-rich gas on improving exercise fatigue and athletic performance.
OBJECTIVE: To investigate the effects of hydrogen-rich gas inhalation prior to high-intensity exercise on proprioception and muscular endurance performance after exercise fatigue. 
METHODS: Through a randomized, double-blind, crossover, and repeated measurement experimental design, 24 healthy men were randomly divided into group A and group B, with 12 in each group. In the first phase of the crossover experiment, group A inhaled hydrogen-rich gas (hydrogen group) for 20 minutes and group B inhaled placebo gas (air; placebo group) for 20 minutes. Then, cycle ergometers were used to establish the fatigue model. Visual analog fatigue scale, heart rate variability, knee joint proprioception (passive position perception, joint motion perception, and muscle force perception) and isometric knee extension muscle endurance were tested before and after intervention. After a 7-day washout period, two groups exchanged intervention methods and the above tests were performed again in the second phase of the experiment. Differences between the results of groups A and B in the two phases were compared, and finally the results of the two phases were integrated to compare the overall differences between hydrogen intervention and placebo intervention. 
RESULTS AND CONCLUSION: In the first phase of the crossover experiment, the visual analog fatigue scale score of the hydrogen group after intervention was significantly lower than that of the placebo group (P < 0.01). The root mean square of the difference between the adjacent R-R, mean low-frequency output power, mean high-frequency output power, and isometric muscle endurance after intervention in the hydrogen group were significantly higher than those in the placebo group (P < 0.05). Passive position perception and joint motion perception after intervention in the hydrogen group were significantly better than those in the placebo group (P < 0.05). There was no significant difference in muscle force perception between the two groups (P > 0.05), but muscle force perception in the placebo group after intervention was significantly worse than that before intervention (P < 0.01). The difference trend of all test results after intervention in the two groups in the first phase of the experiment showed the same results in the second phase of the experiment. The integrated results also showed that the hydrogen group had better test values for the above indicators than the placebo group (P < 0.05). Linear regression analysis showed a positive correlation between post-intervention visual analog fatigue scale scores and passive position perception results (r=0.327, P=0.023), i.e., the higher subjective fatigue level after high-intensity exercise indicated the worse passive position perception results. To conclude, inhaling hydrogen-rich gas before high-intensity exercise can reduce the degree of fatigue after exercise, thereby improving proprioception and muscle endurance performance, which may be a new strategy to reduce the occurrence of injury. And its effectiveness can be achieved repeatedly.

Key words: hydrogen-rich gas, placebo, oxidative stress, exercise fatigue, proprioception, sports injury