## 3 Results  
General characteristics of the participants, age, weight, and size are shown in Table 1.  
Figure 2 presents relative values of LE and SBP maximal dynamic strength (1 RM). There were significant differences between the groups in the knee  
Figure 1: Encoder location and test procedures (1 RM (one-repetition maximum test), Muscle Power). strength (F = 20.085; \(p<0.001;f=0.741\)). The G\({}_{\rm 13-14}\) has a higher LE 1 RM than G\({}_{\rm 11-12}\), (\(p<0.001\)) and G\({}_{\rm 9-10}\), (\(p<0.001\)), and G\({}_{\rm 11-12}\) greater than G\({}_{\rm 9-10}\) (\(p<0.001\)). There are also significant differences between groups in SBP 1 RM (F = 8.509; \(p<0.001\);\(f=0.519\)). G\({}_{\rm 13-14}\) has a higher LE 1 RM than G\({}_{\rm 11-12}\), (\(p<0.001\)) and G\({}_{\rm 9-10}\), (\(p<0.001\)). Figure 3 shows power values at 60% of the LE and SBP 1 RM. Significant differences between groups were found in SPB power (F = 20.408; \(p<0.001;f=0.682\)). G\({}_{\rm 13-14}\) has a higher LE 1 RM than G\({}_{\rm 11-12}\), (\(p=0.003\)) and G\({}_{\rm 9-10}\), (\(p<0.001\)), and G\({}_{\rm 11-12}\) greater than G\({}_{\rm 9-10}\) (\(p=0.019\)). There are also significant differences between groups in LE power (F = 20.085; \(p<0.001;f=0.679\)). G\({}_{\rm 13-14}\) has a higher LE 1 RM than G\({}_{\rm 11-12}\), (\(p=<0.05\)) and G\({}_{\rm 9-10}\), (\(p<0.001\)), and G\({}_{\rm 11-12}\) greater than G\({}_{\rm 9-10}\) (\(p<0.001\)). \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & **Sex** & **Age (Years)** & **Height** & **Weight** & **BMI (kg/m\({}^{2}\))** \\  & **(Female/Male)** & **Age (Years)** & **(cm)** & **(kg)** & **BMI (kg/m\({}^{2}\))** \\ \hline G\({}_{\rm 9-10}\) & 8/8 & 9.53 \(\pm\) 0.51 & 135.41 \(\pm\) 4.52 & 32.30 \(\pm\) 5.43 & 17.55 \(\pm\) 2.51 \\ G\({}_{\rm 11-12}\) & 8/8 & 11.50 \(\pm\) 0.52 & 149.63 \(\pm\) 7.93\({}^{\rm a}\) & 41.59 \(\pm\) 10.40\({}^{\rm a}\) & 18.32 \(\pm\) 2.84 \\ G\({}_{\rm 13-14}\) & 8/8 & 13.53 \(\pm\) 0.52 & 157.20 \(\pm\) 5.48\({}^{\rm abc}\) & 48.15 \(\pm\) 9.39\({}^{\rm abc}\) & 19.58 \(\pm\) 3.78 \\ \hline \multicolumn{6}{l}{\(\overline{\rm G_{\rm 9-10}}\) = age group 9–10 years; G\({}_{\rm 11-12}\) = age group 11–12 years; G\({}_{\rm 13-14}\) = age group 13–14 years; a = \(p<0.05\) difference between G\({}_{\rm 9-10}\) vs. G\({}_{\rm 13-14}\); c = \(p<0.05\) difference between G\({}_{\rm 11-12}\) vs. G\({}_{\rm 13-14}\).} \\ \hline \end{tabular}
\end{table} 
Table 1: Anthropometric characteristics of participants by age group. Figure 2: One-repetition maximum (1 RM) test values for LE (leg extension) and SBP (seated bench press) by age group. G\({}_{\rm 9-10}\) = age group 9–10 years; G\({}_{\rm 11-12}\) = age group 11–12 years; G\({}_{\rm 13-14}\) = age group 13–14 years; *** = \(p<0.001\) difference between marked age group. Repeatability values of 1 RM LEE were good regardless of when they were studied by age (ICC ranged from 0.876 to 0.951; SEM% ranged from 4.52 to 6.64) or gender (ICC ranged from 0.977 to 0.958; SEM% ranged from 5.38 to 6.52). Furthermore, the 1 RM test-retest in LE exercise in total sample demonstrated excellent reliability (ICC = 0.954; SEM% = 7.06). The minimum magnitude of change that would be detectable in the LE exercise was 7.35 to 11.34 kg, or 12.52% and to 18.40% between successive measures and girls showed lower value than boys (MDC% = 14.90; MDC% = 18.07, respectively). Reliability values of the 1 RM test-retest in SBP exercise by age group and gender are shown in Table 3.  
Repeatability values of 1 RM BPS were excellent in each age group (ICC ranged from 0.918 to 0.985; SEM% ranged from 3.30 to 5.01), in girls and boys (ICC = 0.929, ICC = 0.981, respectively; SEM% = 4.92, SEM% = 3.89, respectively) and in total sample (ICC = 0.974, SEM% = 4.67). In addition, the MDC% was different in each age group ranging from 9.15 to 13.87 and boys showed a lower value than girls (MDC% = 10.79).