# Cold-Water Immersion Promotes Antioxidant Enzyme Activation in Elite Taekwondo Athletes
## 1 Introduction  
It is well known that free radicals and reactive oxygen species (ROS) produced in the human body cause cellular damage as well as aging and various chronic disease [1]. However, from a physiological perspective, enzymatic and non-enzymatic systems (antioxidant system) neutralize the harmful effects of ROS [2]. Unlike normal oxygen, ROS are free radicals containing oxygen that are highly reactive. They contain an unpaired electron and have a strong tendency to achieve a stable state, by either taking or giving up an electron. Therefore, when ROS is produced in the body, they easily react with lipids, proteins and DNA, and can cause functional impairments. When ROS attacks cellular membranes, they oxidize unsaturated fatty acids and form lipid peroxides; furthermore, malondialdehydedehyde (MDA) is used as a marker of lipid peroxide [3]. However, ROS are suppressed by antioxidant enzymes, such as superoxide dis-mutase (SOD), glutathione peroxidase (GPX), and catalase (CAT) [4]. Antioxidant enzymes play an important role in defending cells against oxidative damage caused by free radicals [5] that are generated through physical activity through various pathways [6]. Regular and appropriate exercise promotes metabolism, prevents disease, helps with weight management, and strengthens immune function. However, strenuous exercise, such as that performed by well-trained athletes, rapidly increases oxygen consumption and consequently increases oxygen supply by 10-15 times, which induces the production of free radicals [7]. Furthermore, oxygen consumption by muscles during exercise is increased by 10-20 times than at rest [8]. Moreover, it activates ROS that attacks cells, which leads to damages to carbohydrates, fats, proteins, and nucleic acids [9]. In particular, hypoxia or local hypoxia causes transferrin to release iron and exacerbates hemolysis. This alters the metabolism, and these responses increase stress or weaken athletic performance [10]. To minimize such adverse physiological responses, many studies have utilized various approaches to examine methods to reduce exercise-induced fatigue and promote recovery [11; 12; 13; 14; 15]. In particular, cryotherapy or cold-water immersion (CWI), which involves immersion of a part of the body or the whole body, has been researched in various exercise conditions and treatment durations [11; 12; 13; 14; 15]. However, although CWI has more recently been researched in various exercise methods and sports [16; 17], past studies on antioxidant activity-CWI involved swimming [18], kayaking [19], and cryotherapy using a chamber; there were no studies investigating the effects of antioxidant-CWI after an actual match involving electronic protective gear, such as a Taekwondo match. Taekwondo, a combat sport, was introduced as a demonstration sport at the 1988 Summer Olympics at Seoul and the 1992 Summer Olympics at Barcelona. It was confirmed as an official sport at the 2000 Summer Olympics at Sydney. During a Taekwondo match, successful torso punches or kicks and successful head kicks are awarded more points. Thus, a Taekwondo match can result in significant fatigue due to the physical effort involved [20; 21; 22; 23; 24]. An appropriate intensity of training is expected to not only reduce the harmful effects of free radicals but also trigger health benefits by stimulating the immune system [25]. However, free radical production and subsequent lipid peroxidation increase proportionate to oxygen consumption, depending on the intensity of exercise, and are known to be positively correlated with skeletal muscle injury [26]. In other words, vigorous exercise at 80-90% of HRmax [27] induces oxidative stress one way or the other, thereby affecting lipid peroxidation and antioxidant enzymes. Although studies have investigated injuries based on athletic proficiency, sex, body weight, age, mechanism, involving body part, situation, and years or experience [28; 29], only a handful of studies were conducted on martial arts athletes.