## 4 Discussion and Conclusions  
Contact with cold or icy water provides numerous health-related benefits by triggering a physiological response in the body aimed at homeostasis. It is known what happens in the human blood after a single immersion in icy water [29] and after regular  
Figure 4: Hormone change dynamics in the group of winter swimmers and the control group (phase 1 vs. phase 3). winter swimming [30]. Another relevant issue concerns the psychological responses of winter swimmers. While answering the research questions posed, the authors indicated that individuals who regularly practised winter swimming seemed to present lower levels of the depression-dejection scale while, at the same time, having higher levels of vigor (question 1). However, life satisfaction levels did not differ between winter swimmers and controls (question 2). It was also implied that a single immersion in cold water by regular winter swimmers brought about considerable improvements in mood: immediately after emerging from the water, all negative emotional states were reduced while vigor improved. This better mood (in addition to the vigor score) persisted for at least 24 h after immersion, as evidenced in measurement 3. When comparing the changes in the results (between the measurements performed 24 h before cold-water immersion and 24 h after the immersion), the authors indicated that in the winter swimming group, the results were significantly reduced between the two measurements for tension-anxiety and fatigue as compared with the control group (question 4). Similar results were obtained by [PERSON] et al. [4]; they reported that after 4 months of immersing in cold water, winter swimmers exhibited more vigor and less fatigue than the control group individuals. The presented study confirms the assumption that adaptation to cold water contributes to a weaker response to stressors arising in daily life (lower depression-dejection score). In 2018, a case study was published demonstrating for the first time the effect of cold-water swimming in open areas on reducing symptoms of depression [8]. Summarizing the results obtained from the POMS questionnaire, one could conclude that regular winter swimming positively influences emotional states. Among the explanations for the observed changes is the activation of the parasympathetic nervous system. The results of this study indicate that systematic winter swimmers exhibit significantly higher blood adrenaline concentrations as compared with the individuals who did not practise winter swimming. Adrenaline is the hormone responsible for the immediate stress response of the body in an emergency situation: in this case, repeated contact with cold water. The effect of adrenaline is short-lasting, but among winter swimmers, the frequent contact with cold water influenced the activation of the sympathetic nervous system and increased blood adrenaline concentrations as compared with the control group; this confirms that the stimulus was sufficient to induce significant adaptive changes in the activity of the sympathetic nervous system and the production of adrenaline. According to [PERSON] [31], owing to the increase in catecholamines, cold-water swimming can be curative for depression as it activates the sympathetic nervous system, as well as increases the concentration of noradrenaline and endorphins. A recent study involving 1114 female cold-water swimmers demonstrated that this hobby alleviated the mood fluctuations associated with menstruation and menopause [32]. Moreover, in the own study, 24 h after cold-water immersion, the winter swimming group was characterized by a significant reduction in noradrenaline and adrenaline concentrations and by a slight increase in cortisol concentration, as compared with the control group. Of interest, a slight increase in serotonin levels in the control group was observed, unlike in the winter swimming group. Dopamine levels remained unchanged.