## 2 Materials and Methods
### Statistical Analysis  
Before performing the statistical analysis, it had to be ensured that the dataset was normally distributed. An Anderson-Darling test was conducted on all of the computed values for each investigated parameter to determine if it was normally distributed [24]. The significance level of the normality test was \(\alpha=0.05\). It was found that all the examined parameters regarding all dancers and all measurements were normally distributed. The mean and relative standard deviation (CV) values were calculated from the examined angular parameters' ROM values in each dancing session. The mean value characterized the overall image of the motion, while the relative standard deviation gave an estimation for the regularity of the movement. Note that only the mean values were considered in the statistical analysis in the case of the maximum force and cycle time. A within-study design was adopted to compare the differences between the dancing sessions. One-way repeated-measures analysis of variance (ANOVA) was applied on the kinetic (maximum of the GRF and cycle time) and kinematic (ROM of knee flexion angle, ROM of hip flexion angle, and ROM of pelvis tilt angle) parameters on all available time points (Sessions 1 to 10). The significance level was \(\alpha=0.05\), whereas, as a pilot study, the ANOVA test with a significance level of \(\alpha=0.1\) was also performed to examine if weakening the criteria affected the results. The null hypothesis was that the investigated parameters did not change at either a 95% or a 90% confidence level as dancers had to repeat the dancing sessions several times. A Bonferroni post-hoc test was performed on the kinematic data, to examine the differences between each session separately and investigate which time sequence had a stronger effect on the change [25; 26]. A between-study design was applied to evaluate the balance tests, where two-way ANOVA was performed on the COP parameters. The factors were the measurement time (before or after) and the visual feedback (_eyes opened_ or _eyes closed_). The aim of the statistical analysis was to examine the common effect of the two factors on the balancing ability. The null hypothesis was that the COP parameters did not change at the 95% confidence level after the dancing sessions, which means a significance level of \(\alpha=0.05\). \begin{table}
\begin{tabular}{l l l} \hline \hline
**Parameter Name** & **Description** & **Unit** \\ \hline COP \(x\) range & The difference between the maximum and minimum coordinates & (mm) \\  & of COP in the \(x\) anterior-posterior direction & (mm) \\ \hline COP \(z\) range & The difference between the maximum and minimum coordinates & (mm) \\  & of COP in the \(z\) medio-lateralis direction & (mm\({}^{2}\)) \\ \hline COP area & The area of the ellipse that contains 95\% of the data & (mm\({}^{2}\)) \\ \hline COP \(x\) max + & Maximum deviation of COP in the \(x\) direction & (mm) \\  & from the mean in the positive direction & (mm) \\ \hline COP \(x\) max – & Maximum deviation of COP in the \(x\) direction & (mm) \\  & from the mean in the negative direction & (mm) \\ \hline Path of COP & The path of the COP during the measurement in the \(x\)-\(z\) plane & (mm) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Examined COP parameters. The repeated-measures ANOVA tests' results showed significant changes during the dancing sessions in the dominant and nondominant knee flexion angles (\(p=0.044\) and \(p=0.003\)) and nondominant hip flexion angles (\(p=0.005\)). Lowering the significance level to 90%, it could be seen that all ROMs of the joint angles changed significantly between the first and tenth dance sequence. However, the \(\eta^{2}\) values of the averages of the ROMs indicated that the effect size was small. The results of the Bonferroni post-hoc test showed that the difference between the sixth and the ninth dance was the largest in the dominant knee joint angle, with the difference being significant (\(p=0.002\)).