## 4 Discussion  
The purpose of this study was to examine the effect of combined balance and multi-directional pyometric training in male and female preadolescent soccer athletes. Overall, the results did not confirm the main hypothesis since the postural balance ability and the lower limb explosive performance of athletes did not show a significant improvement post-training. Further, the absence of a significant interaction between training and visual restriction leads to the rejection of the hypothesis, referring to the possible benefit of the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Jump** & **PRE** & **POST** & **\%\(\Delta\)** & **Cohen’s d** \\ \hline Jump height (cm) & & 20.4 \(\pm\) 4.4 & 19.6 \(\pm\) 3.8 & \(-\)3.9\% & 0.18 \\ Maximum vertical force (N) & & 1023 \(\pm\) 275 & 1051 \(\pm\) 271 & +2.7\% & 0.10 \\ Maximum impulse (N-sec) & & 104 \(\pm\) 30 & 105 \(\pm\) 30 & +1.0\% & 0.04 \\ Mean power (Watt) & & 190 \(\pm\) 81 & 190 \(\pm\) 64 & 0\% & 0.02 \\ Maximum power (Watt) & & 1764 \(\pm\) 578 & 1797 \(\pm\) 561 & +1.5\% & 0.06 \\ \hline Jump height (cm) & & 17.3 \(\pm\) 3.5 & 16.7 \(\pm\) 3.6 & \(-\)3.5\% & 0.16 \\ Maximum vertical force (N) & & 1115 \(\pm\) 271 & 1104 \(\pm\) 275 & \(-\)1.0\% & 0.04 \\ Maximum impulse (N-sec) & & 97 \(\pm\) 27 & 97 \(\pm\) 27 & 0\% & 0.03 \\ Mean power (Watt) & & 369 \(\pm\) 136 & 401 \(\pm\) 148 & +8.7\% & 0.23 \\ Maximum power (Watt) & & 1743 \(\pm\) 524 & 1737 \(\pm\) 499 & \(-\)0.3\% & 0.01 \\ \hline \multicolumn{5}{c}{\%\(\Delta\): Post- vs. pre-measurements. Data are mean \(\pm\) SD.} \\ \end{tabular}
\end{table} 
Table 4: Parameters of lower limb explosive performance before (PRE) and after (POST) the combined balance and multidirectional pyometric training intervention. Figure 2: Individual change (%\(\Delta\): post- vs. pre-measurement) in lower limb explosive performance during jumping (**(a)**: CMJ, **(b)**: SJ) in the preadolescent soccer athletes (note: to facilitate visual inspection of the graphs, the first 10 series of data refer to the male and the next 10 series of data to the female soccer athletes). training intervention in processing visual information for postural control regulation in preadolescent soccer athletes. The present findings show that the combined training intervention resulted in a significant deterioration of static two-legged balance due to a 39% increase in the anteroposterior CoP sway range. On the other hand, the CoP path length and mediolateral sway range showed a non-statistically significant increase by 6.4% and 36%, respectively, whereas single-legged static balance performance was found to be slightly, albeit not significantly, improved after training. In the literature, no studies combining balance and pyometric training could be found in soccer, except for two recent studies in other team sports. In particular, and in agreement with our findings, no significant change was found in single-legged quiet stance balance ability in 15-16-year-old female regional-level basketball athletes following 8-week combined balance and pyometric training [27]. On the contrary, an improvement in dynamic anteroposterior and mediolateral CoP sway was seen after landing either from a horizontal or a lateral jump for short distance (40% of height) in elite male badminton players, who participated in a combined intervention (6 weeks at a frequency of 3 days/week for 1 h) [41]. In the present study, the training volume was the result of balance and pyometric training exercises, but in that study [41], pyometric training was twice the volume of the respective balance training's volume. Moreover, the present findings on static balance performance are in disagreement with a previously reported training intervention (8 weeks, 24 sessions) [21], which had several similarities in reference to balance exercises and dynamic stabilization tasks as the ones administered in the current study (see Table 1).