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oxygen saturation (SpO2) was reported to be significantly decreased with bicycle training in healthy adults11). On the basis of these findings, we hypothesized that the intake of high-concentration oxygenated water before and during exercise could prevent SpO2 reduction during exercise in a hypoxic environment.Therefore, the current study aimed to evaluate changes in blood oxygen saturation during exer-cise under hypoxic conditions after consumption of high-concentration oxygenated water in normal adults.Materials and MethodsThis randomized placebo-controlled single-blinded trial was performed from July to August 2021. The current study was approved by the institutional human ethics committee (2021-77) at Juntendo University School of Health and Sports Science, and was in compliance with the Declaration of Helsinki and existing legal regulations. Written consent was obtained from all participants before their enrollment. The inclusion criteria were as follows: healthy men or women aged > 20 years. The exclusion criteria were as follows: body temperature > 37.5 °C; SpO2 < 95%; systolic blood pressure > 145 mmHg or diastolic blood pressure < 90 mmHg; history of heart or pulmonary disease; and other comorbidities, disorders and diseases that could affect the results. We recruited 22 partic-ipants, who were randomly assigned to either the control group (drinking normal mineral water) or the OX group (drinking oxygenated mineral water with high oxygen concentration). Participants were blinded from group allocation. Age, sex, body height, body weight, smoking history, and sports habits were collected as demographic data.InterventionA bottle of normal mineral water (control group) or oxygenated mineral water (OX group) was given to participants before the experiment began. An OXMAX (WellsO2 Inc, Tokyo, Japan) oxygen capsule was used to make the oxygenated water. The same commercially available bottled mineral water at room temperature was used for the exper-iments in both groups. The experiment was conducted at the High-Alti Training Studio (High Altitude Management Co., Ltd, Tokyo, Japan), where a normobaric hypoxic environment (oxygen partial pressure of 15.2%, equivalent to 2600 m above sea level) was available. During the experi-ment, participants were asked to walk for 30 min on a self-propelled treadmill (Speedboard ProXL, Speed Fit, USA) under normobaric hypoxic condi-tions, and during exercise, SpO2 and pulse rate (PR) were measured every 2 s using a pulse oxim-eter (RingO2, Viatom Technology Co. Ltd). Exer-cise intensity was set at 11-13 on the subjective fatigue Borg scale12), and the score was recorded every 3 min during exercise. The participants were instructed to drink 200 mL of water 10 min before walking, 100 mL 6 min before walking, 100 mL 1 min before walking, and 100 mL 10 min after starting walking. Participants entered the hypoxic room 5 min before the exercise and left the room after 30 min of walking exercise. After the exercise period, participants rested for 10 min in a normoxic environment (Figure 1).Before the experiments, the average SpO2 and PR values under the normal environment were used as baseline values. These were analyzed every 5 min. The mean values for each phase were compared between the two groups. In addition, the walking distance displayed on the treadmill monitor at the end of the exercise period was recorded and compared between the two groups. We used two-way analyses of variance for comparing the mean quantitative variable changes. A p-value less than 0.05 was considered to indicate statistical significance. Statistical analyses were performed using GraphPad Prism 9 (GraphPad Software Inc., La Jolla, CA, USA).Sixteen men and six women participated in this study. The mean age (standard deviation; SD) was 22.4 (2.73) years. The mean height (SD) was 167.1 cm (8.0) and mean weight (SD) was 63.5 kg (15.3), as shown in Table 1. Of the 22 participants, 3 were smokers. The participants, on average, exercised for 2.2 (2.15) days per week. The resting SpO2 values (95% confidence interval [CI]) in both the control and OX groups were 97.2% (1.49) and 95.0% (3.98), respectively, and no significant differ-ence was observed (P = 0.13).229Statistical analysisResults