Purpose: We investigated whether a 4-day intake of hydrogen-rich water (HRW) improves finswimming performance and alters physiological and perceptual markers including blood lactate, rating of perceived exertion, and oxidative stress. Methods: Eight females and 4 males, age 21 (5) and 19 (1) years, maximal oxygen consumption 45.0 (2.5) and 52.2 (1.7) mL·kg-1·min-1, performed 3 sets of 4 reps of 50-m surface finswimming sprints in a morning session, and a 400-m surface time trial in the afternoon on the same day. Participants consumed either HRW (hydrogen concentration 0.9 ppm) or placebo, starting 3 days prior to the experimental sessions. Intake was 1260 mL per day for 3 days, and 1680 mL on the day before the 400-m time trial. After each 4 × 50-m set and 400-m trial, blood lactate and rating of perceived exertion were measured. Oxidative stress was evaluated by plasma protein carbonyls at scheduled time points. After a 1-week washout period, the experiment was repeated with participants receiving the alternate intervention. Clinical trials registration: NCT05799911. Results: HRW did not significantly improve morning 50-m sprint times (0.5%, P = .12) but afternoon 400-m time trial was improved by 0.6% (P = .003). The differences between HRW and placebo administration on blood lactate, rating of perceived exertion, and protein carbonyls were not significant (all P = .12). Conclusions: Short-term HRW supplementation provides a modest yet meaningful performance improvement of 0.6% in middle-distance (400-m surface) finswimming. However, its effects on repeated sprint performance, blood lactate, perceived exertion, and oxidative stress appear limited.
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