## 5 Results  
Before selecting the parametric test for the HR data, we performed the Shapiro-Wilk normality of distribution test for all phases (before, during, and after the task). The obtained results (before--\(p\) = 0.0036, during--\(p\) = 0.7600, and after--\(p\) = 0.7530) led to the rejection of the normality hypothesis in the before case. Thus, the statistical analysis was completed by performing the Mauchly's and JNS sphericity test performed to evaluate the differences of variances between the phases. The results (JNS = 44.06, \(p\) < 0.001) indicated that the use of parametric tests was not applicable. Therefore, we decided to use [PERSON]'s test in further analyses.  
The [PERSON]'s test results shown in Figure 10 confirm significant differences between the three phases of the experiment (Fr = 23.68; \(p\) < 0.001). The results of [PERSON]'s test were supported with Dunn-Bonferroni and Conover post-hoc tests (see Table 1) which proved that the heart rate before performing the task was significantly lower than the heart rate during the task (\(p\) < 0.001) and after the task (\(p\) < 0.001).  
Figure 11 shows differences between the perceived stress levels in the subsequent phases of the task. The median of perceived stress level before the task was 2, during the task was 4, and after the task was 1.5. The highest perceived level of stress was 6 for participants in the \"during the task\" phase.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{2}{c}{**Dunn-Bonferroni**} \\ \hline \multirow{4}{*}{
\begin{tabular}{c} \\ \end{tabular} } & \(p\) & Before the task & During the task & After the task \\  & Before the task & & \textless{}0.001 & \textless{}0.001 \\  & During the task & \textless{}0.001 & & 0.953 \\  & After the task & \textless{}0.001 & 0.030 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Results of post-hoc tests of the differences between the heart rate measured in subsequent phases of the experiment.  
Figure 10: Results of Friedman Two-Way Analysis of Variance by Ranks of the differences between the heart rate measured in subsequent phases of the experiment. Q\({}_{1}\)-first quartile, Q\({}_{3}\)-third quartile.  
The [PERSON]'s test results shown in Figure 11 confirm significant differences between the three analyzed phases (Fr = 18.35, \(p\) < 0.001) and they were supported by [PERSON] and Conover post-hoc tests (see Table 2) which proved that the perceived stress level during performing the task was significantly higher than the stress level before the task (\(p\) < 0.001) and after the task (\(p\) < 0.001).  
The results of [PERSON]'s rank correlation analysis presented in Table 3 proved that the relationship between the heart rate and perceived stress level during the task was statistically significant (\(p\) = 0.005).  
The median power of total linear acceleration, angular velocity, and EOG signal before the task was 5.362 \(\times\) 105 s\({}^{2}\), 4.260 \(\times\) 106 s\({}^{2}\), and 7.533 \(\times\) 103 s\({}^{2}\), and the median power of total linear acceleration during the task was 5.483 \(\times\) 105 s\({}^{2}\), 4.330 \(\times\) 106 s\({}^{2}\), and 1.644 \(\times\) 105 s\({}^{2}\) (see Figures 12-14).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **Dunn-Bonferroni** & \\ \hline \multirow{4}{*}{
\begin{tabular}{c} **Front** \\ **  
Figure 12: The differences between the power of EOG before the task and during the task.  
Figure 13: The differences between the power of linear acceleration before the task and during the task.