# Cold-Water Immersion Promotes Antioxidant Enzyme Activation in Elite Taekwondo Athletes
## 4 Discussion
### Variation of MDA Concentration after CWI for Taekwondo Athletes  
In general, ROS are released from the electron transport chain in the mitochondria, even at rest [3], and they eventually attack the cell membrane and nucleus and form lipid peroxides. Moreover, secondary ROS, produced as a result of ROS activation surpassing the defense system with antioxidant enzymes, stimulate the peroxidation of lipids containing unsaturated fatty acids in cell membranes, thereby elevating the concentration of MDA, the final metabolite of lipid peroxide, and induce injuries [41]. After exercise, ROS concentration can increase so much as to induce acute injuries of muscle fibers and connective tissues, leading to muscle ache, delayed recovery, and diminished exercise performance [42]. Previous studies have examined the effects of types of cryotherapy on such lipid peroxides produced through exercise and antioxidant enzymes [43; 44].  
Cryotherapies are used for therapeutic purposes in sports, and their effects differ according to the method, duration, treatment site, and the individual's level of physical activity. Among various cryotherapies, crushed ice pack, ice massage, and CWI are the most effective [45]. In a study examining changes of MDA concentration after cold treatment, no change in MDA was found after performing high-intensity jump exercises between the untrained group and the group trained in the exercise; although the levels of lipid peroxidase in muscles, as measured by changes in MDA concentration, varied widely, there were no differences between the two groups [46]. These results seem to be attributable to excellent physical defense regulation in the athletes as a result of prolonged chronic training. These results are consistent with our findings. In this study, MDAconcentration immediately after the match was lower than that before the match, but reduced MDA concentration did not differ between after CWI and after rest. However, another study reported that ice-water immersion after 30 min of cycling lowered lipid peroxide concentration [44], which contradicts the results of our study and that of the previously mentioned study [47].  
In 2003, [PERSON] et al. reported that MDA production is influenced more by exercise intensity or duration, as opposed to the type of exercise performed [47]. Thus, it seems that MDA concentration after jump exercises or a competition that can be performed in a short time [47], and that after a Taekwondo competition, are not markedly influenced by cold treatment or CWI. The reduction of MDA concentration after 30 min of cycling exercise, as reported in a prior study [43], seems to have been a result of the longer duration of the exercise.  
There are various study findings regarding long-term chronic training, where some studies report that it bolsters an individual's physical defense mechanisms and decreases MDA even if they engage in exhaustive exercise [48], while other studies report that ROS as well as antioxidant enzymes are produced after exhaustive exercise [49].  
This suggests that the gap in the changes of MDA caused by exercise may be attributable to various factors, including study design. Furthermore, the most crucial factor is speculated to be the level of proficiency of participants for the particular type of exercise or perceived exercise intensity; in athletes who underwent prolonged professional training, local CWI seems to have been inadequate to reduce intracellular-intravascular flow to promote recovery from cellular or membrane injuries from free radical production triggered by increased oxygen consumption in the active muscles during a game.