## 4 Discussion  
The results of this systematic review and meta-analysis confirm that multiple physical training interventions can significantly improve physical performance in children and adolescents who practice handball. Among these, pylometric training and resistance band exercises stand out, having demonstrated substantial positive effects on key variables such as peak power, jump performance (CMJ and SJ), and sprint performance. Specifically, resistance band training showed robust improvements in both countermovement jump (SMD = 1.69) and squat jump (SMD = 1.46), with low heterogeneity (I\({}^{2}\) = 14%), supporting the strength of the observed effects. These findings align with evidence reported in related sports contexts, such as basketball, where studies like [PERSON] et al. [101] documented improvements in vertical jump and anaerobic performance following pylometric interventions, and volleyball, where [PERSON] et al. reported significant increases in jump power and spike speed in adolescent players after Thera-Band programs [102]. From a variable-specific perspective, pylometric training showed systematic improvements in peak power (SMD = 1.41), a central variable for executing explosive actions such as jumps, throws, and changes in direction. Regarding sprint performance, differentiated effects were observed, depending on the distance: significant improvements were noted in 5 m (SMD = \(-\)1.22) and 30 m sprints (SMD = \(-\)3.15), suggesting adaptations in both initial acceleration and sustained speed over longer distances. This pattern may be explained by progressive improvements in intermuscular coordination, the efficient recruitment of high-threshold motor units, and strengthening of the stretch-shortening cycle--physiological mechanisms widely recognized in the literature as outcomes of systematic exposure to pylometric stimuli [103; 104]. These adaptations, far from being transient, represent structural and functional enhancements of the neuromuscular system, particularly relevant in developing populations where plasticity mechanisms are highly responsive to targeted stimuli. Similarly, [PERSON] et al. [6] demonstrated comparable effects in adult handball players, suggesting that physiological adaptations related to strength and power can be safely and effectively induced from early developmental stages, provided that the training load design adheres to principles appropriate for children and youth. This approach contrasts with previous reviews focused on adult populations or technical-tactical interventions, without thoroughly addressing the specificity of physical training in childhood and adolescence. This distinction grants the present study added value and direct applicability for designing programs in formative categories. In terms of vertical jump performance, both CMJ and SJ showed positive responses to interventions, indicating the reinforcement of the stretch-shortening cycle, a core component in explosive movement efficiency. In line with the emerging literature, resistance band interventions have been established as an effective and safe strategy for developing explosive physical qualities in young athletes, particularly in contexts with infrastructure limitations or low-impact requirements. Their low cost, portability, and ease of implementation make them highly accessible tools in schools, clubs, and training academies. Although previous studies, such as those by [PERSON] et al., [PERSON] et al., and [PERSON] et al., have reported positive effects on vertical jump performance following programs incorporating or simulating resistance band characteristics [101; 105; 106], these findings should be interpreted with caution. [PERSON] et al. [105], for instance, reported improvements in explosive strength and change in direction in youth handball players, but their systematic review design did not include a quantitative analysis of effects. [PERSON] et al.