## 3 Results  
There were no statistically significant differences in baseline dominant-side strength between the CG and the EG, with a mean value of approximately 12.4 kg. Similarly, the non-dominant side strength showed no significant intergroup differences, presenting an average of 11.1 kg. Vertical jump performance ranged between 40.5 and 42.4 cm in both groups, with no statistically significant differences observed. These findings, presented in Table 2, indicate homogeneity between the independent samples across the primary study variables. The EG received the intervention for 7 weeks, generating significant differences between the initial and final values: The absolute strength of the dominant side initially registered averages of 12.4 kg, and at the end of the intervention, there was an increase of 14.5 kg, with significant differences (\(p<0.01\)). The absolute strength of the non-dominant side presented mean values of 11.1 kg, and after the intervention time, it increased to 13.8 kg, likewise with significant differences between means (\(p<0.01\)). Vertical jump height increased from an initial average of 42.4 cm to 45.8 cm following the intervention, with a significant difference observed between pre- and post-test measurements (\(p<0.01\)). In contrast, the CG showed no statistically significant differences between pre- and post-test values in any of the three variables assessed (Table 3). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Weeks** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** \\ \hline Warm-up—minutes & & 15 & 15 & 15 & 15 & 15 & 15 & 15 & \\ \hline Series & P & 2 & 2 & 2 & 3 & 3 & 3 & 3 & P \\ \hline Repetitions & R & 5 & 6 & 8 & 10 & 12 & 12 & 10 & S \\ \hline Eccentric tension in & - & 2 & 2 & 3 & 3 & 5 & 5 & 3 & - \\ \cline{3-8} seconds & T & & 2 & 2 & 2 & 1 & 1 & 1 & 1 & E \\ \hline Rest in minutes & S & 5 & 5 & 5 & 5 & 5 & 5 & 5 & S \\ \hline Total time in minutes & & 23 & 23 & 23 & 24 & 25 & 25 & 24 & T \\ \hline \hline \end{tabular}
\end{table} 
Table 1: NHE training protocol. An important mean difference is evident between the vertical jump and the absolute strength of the final dominant and non-dominant side when comparing the results between independent groups (\(p\) < 0.05), as described in Table 4.  
The absolute strength values measured in kilograms on the dominant and non-dominant sides in the EG showed a slight increase, particularly in the disciplines of sport climbing, basketball, football, and sprinting (Figures 4 and 5). An increase in mean vertical jump height was observed in the EG corresponding to sport climbing, basketball, sprinting, and football, indicating performance improvements across these disciplines following the intervention (Figure 6). In Table 5, the repeated measures ANOVA shows that there was a significant difference in the three variables: dominant absolute strength (F = 6.6; \(p\) = \(<\)0.01; \(\mathrm{np^{2}}\) = 0.044); non-dominant (F = 8.3; \(p\) < 0.01; \(\mathrm{np^{2}}\) = 0.07); and explosive strength (F = 19.03; \(p\) < 0.01; \(\mathrm{np^{2}}\) = 0.14); These results highlight a meaningful effect of the time \(\times\) group (T \(\times\) G) interaction, suggesting that the intervention contributed to performance gains over time in the experimental group. However, the time \(\times\) sport discipline \(\times\) group (T \(\times\) S \(\times\) G) interaction did not yield statistically significant differences in any of the three variables, indicating that the effect of the intervention varied across sports and did not follow a consistent pattern. This variability suggests that sport-specific factors may influence the responsiveness to eccentric strength training protocols.