## 3 Results  
The first step was to examine whether the individuals in the study groups differed significantly from one another at the moment of the first measurement (before winter swimming). As for the results of the POMS questionnaire, which examines emotional moods, the first measurement (Table 2) revealed significant differences in the scales of depression-dejection and vigor. In all the cases, the differences were in favor of the winter swimming participants. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline  & **Group** & **Phase 1** & **Phase 2** & **Phase 3** & **Statistical Analyses** \\ \hline \multirow{4}{*}{Tension–Anxiety} & Control & 1.51 \(\pm\) 0.80 & – & 1.39 \(\pm\) 0.70 & I: t(28) = 1.461; \(p=0.926\) \\  & & & & & II: F(1, 30) = 9.410; \(p=0.005\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.239\) \\  & Winter swimmers & 1.18 \(\pm\) 0.44 & 0.71 \(\pm\) 0.35 & 0.69 \(\pm\) 0.30 & III: F(1, 30) = 3.286; \(p=0.080\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.099\) \\  & & & & IVa: F(2, 30) = 17.776; \(p<0.001\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.542\) \\  & & & & & IVb: \(\chi^{2}(2,30)=16.3\); \(p<0.001\) \\ \hline \multirow{4}{*}{Depression–Delejection} & Control & 1.02 \(\pm\) 0.87 & – & 0.97 \(\pm\) 0.84 & I: t(28) = 2.371; \(p=0.050\) \\  & & & & & II: F(1, 30) = 4.073; \(\mathrm{\SIUnitSymbolMicro_{p}}^{3}=0.053\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.120\) \\  & & & & & III: F(1, 30) = 2.011; \(p=0.166\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.063\) \\  & & & & & IVa: F(2, 30) = 4.942; \(p=0.014\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.248\) \\  & & & & & IVb: \(\chi^{2}(2,30)=8.52\); \(p<0.001\) \\ \hline \multirow{4}{*}{Anger–Hostility} & Control & 1.11 \(\pm\) 0.79 & – & 0.86 \(\pm\) 0.67 & I: t(28) = 0.622; \(p=1.000\) \\  & & & & & II: F(1, 30) = 13.479; \(p=0.001\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.310\) \\  & & & & & III: F(1, 30) = 2415; \(p=0.131\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.075\) \\  & & & & & IVa: F(2, 30) = 10.446; \(p<0.001\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.411\) \\  & & & & & IVb: \(\chi^{2}(2,30)=8.11\); \(p=0.017\) \\ \hline \multirow{4}{*}{Vigor} & Control & 1.92 \(\pm\) 0.68 & – & 1.91 \(\pm\) 0.55 & I: t(28) = \(-4.151\); \(p=0.002\) \\  & & & & II: F(1, 30) = 0.017; \(p=0.896\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}>0.001\) \\  & & & & & III: F(1, 30) = 0.002; \(p=0.965\); \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}>0.001\) \\  & & & & & IVa: F(2, 30) = 3.699; \(\mathrm{\SIUnitSymbolMicro_{p}}^{2}=0.198\) \\  & & & & & IVb: \(\chi^{2}(2,30)=5.73\); \(p=0.057\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Descriptive statistics: POMS. Variables are shown as mean values \(\pm\) standard deviation (SD). As for the results of the SWLS questionnaire, which examines the level of satisfaction with life (winter swimmers: SWLS of 21.4 \(\pm\) 5.69; control group: SWLS of 20.94 \(\pm\) 8.39), no statistically significant differences were found between the study groups (\(p\) > 0.05). The results of the analysis using \(t\)-tests indicated significant differences between the study groups for adrenalaine. The winter swimmers were characterized by higher concentrations of this hormone (Table 3). No statistically significant differences were indicated in the concentrations of the other hormones (noradrenaline, dopamine, serotonin, and cortisol) (\(p\) > 0.05). With reference to the GLM analysis concerning the results of the POMS tests (Table 2), the following differences were reported (\(p\) < 0.05). As for tension-anxiety, a decrease in this scale (by 0.3 points) was noted in all subjects at measurement 3 (24 h after). Additionally, a trend for the time \(\times\) group interaction was reported. The results indicate that the reduction in the perceived tension-anxiety in the winter swimming group (by 0.49 points; post hoc Tukey: \(p\) = 0.009; Wilcoxon: \(p\) = 0.001; \(\tau_{\rm Hb}\) = 0.997) is significantly greater than that in the control group (by 0.13 points; \(p\) > 0.05).