Every player trains intensely to excel and constantly seeks ways to improve performance. Systematic self-management is key to becoming a competitive athlete and directly impacts performance improvement [1]. Three main categories of factors, namely technical factors, psychological factors and physical factors determine soccer players’ performance. The technical factors include technology, tactics, and self-management. The psychological factors include image training, teamwork, confidence, and routines. Physical factors control nutrition, training methods, recovery management, and dietary intake [2]. Factors that determine physical factors have long been considered critical in determining performance and have the advantage of being easier to control than other factors [3].

Ergogenic aids are supplements administered to improve efficiency related to exercise performance, and the sports world has recently shown high interest in the application of exercise supplements [4]. Ergogenic aids supplement for the athlete's lack of meals and nutrients during the day, and meet the requirements of nutrients which are depleted by high-intensity training. They also improve athletic performance by improving endurance, reducing recovery time, preventing fatigue and disease, and preventing infection [5]. According to a recent study on the use of ergogenic aids among 100 Norwegian national athletes in various sports, 84% of surveyed athletes used ergogenic aids [6]. Thus, various drinks related to water intake have been developed and used in the market to improve athletic performance.

Functional sports drinks such as hydrogen water and ion drinks are being released as ergogenic aids [7]. Hydrogen water is rich in dissolved hydrogen, which is known to protect DNA and RNA by removing active oxygen from the body and it promotes the biosynthesis of adenosine triphosphate [8]. However, most studies on hydrogen drinks have focused on blood components, and studies analyzed from the perspective of respiratory variables are scarce. In addition, in previous studies, most of the concentration of hydrogen water was 0.7 ppm to 1 ppm. Only a relatively low concentration of hydrogen was dealt with, and few studies have been conducted on highly concentrated hydrogen water [1], [9], [10].

Active oxygen protects the body by providing immunity against foreign substances entering the body; however, excess of it could lead to host cell damage. In other words, excessive active oxygen in the body causes oxidative stress, leading to diseases such as cancer, diabetes, heart disease, and high blood pressure. However, hydrogen water combines with active oxygen to form harmless water to protect the body. It is known that active oxygen can be produced as a byproduct of oxygen metabolism, in which living organisms generate energy through breathing, and about 2–5% of the oxygen consumed is converted into free radicals during the metabolic process [11]. The changed radicals are highly reactive due to the specificity of the electronic arrangement of oxygen molecules, which destroy lipids, proteins, sugars, and nucleic acids, cause chronic oxidative damage to tissues, impairing cell function, and cause various chronic diseases such as aging and cancer [12], [13]. Free oxygen is generated immediately after muscle contraction and endurance exercises; however, few studies have presented direct evidence [14]. Since this method of quantifying active oxygen generated by physical activity is complicated, most previous studies have estimated the production of malondialdehyde (MDA), an indicator of oxidative damage, during or after exercise [15], [16].

Soccer is a high-intensity sport that lasts more than 90 minutes, and many studies have recommended the intake of exercise supplements since fatigue byproducts are produced along with a lot of energy consumption during the game [17]. In addition, the player is affected by various environments since it is an outdoor game and requires players to perform instant and explosive movements with constant muscle contraction and relaxation for a long time. Therefore, hydration is an essential factor in controlling body temperature and maintaining metabolism for soccer players. Above all, hydration is necessary to maintain performance [18]. To overcome performance degradation and improve exercise performance, it is necessary to consider drinking highly concentrated hydrogen water. Common characteristics of intermittent sports such as soccer are reduced distance and time in the second half of the game, decreased blood sugar, decreased exercise performance, and accumulated fatigue [19], [20].

Studies have shown that hydrogen water (HW) can protect the human body from oxidative stress. However, more studies are needed to reflect the specificity of respiratory gas variables and sports. Few studies have been conducted on highly concentrated hydrogen water. In addition, the direct effects of hydrogen water intake on active oxygen, blood variables, and exercise performance were insufficient. Therefore, this study aimed to contribute towards improving the performance by analyzing the effect of high-concentrated hydrogen water intake on active oxygen and athletic performance of male adult soccer players.