## 4 Discussion
Most do not incorporate objective measures of pubertal stage nor adjust training loads to participants' biological profiles, limiting both evidence quality and the potential for designing truly personalized and effective programs. Advancing toward greater systematization and coherence in intervention design is therefore not only desirable but essential. The effective integration of formative principles proposed by LTAD, along with progressive load criteria and contextual adaptability, is key to optimizing training effects and ensuring safe, sustained, and transferable physical development. A relevant aspect emerging from this review is the limited integration between physical training content and the technical-tactical components of handball. This methodological separation represents a critical weakness, given that physical capacities--such as explosive strength, speed, or agility--are always expressed in situational contexts requiring decision-making, environmental adaptation, and coordinated execution under high variability. Consequently, training programs that artificially fragment these components risk generating adaptations that do not effectively transfer to real-game situations [107]. It is therefore essential for future research to advance toward integrated or contextualized approaches, where physical conditioning is developed through representative tasks aligned with handball's internal logic and perceptual-motor demands. From an applied perspective, the findings of this review offer valuable guidance for coaches, educators, and sports planners working with youth athletes. Psychometric and resistance band interventions, which showed positive effects on physical performance--particularly in vertical jump, power, and speed--can be progressively incorporated, provided that fundamental principles such as alignment with biological age, load management, and integration with technical content are respected. Their low cost and versatility make these strategies viable even in schools or clubs with limited infrastructure, without compromising stimulus quality. Finally, it is imperative that future research addresses the key methodological gaps identified. Studies with greater experimental controls are recommended, incorporating longitudinal follow-ups to assess the sustainability of adaptations and considering moderating variables such as gender, bone age, pubertal stage, and competitive level. Additionally, it would be desirable to include functional indicators evaluating the transfer of physical improvements to situational performance, thereby validating training programs that are truly effective, safe, and adapted to the context of young handball players. Comparative evidence from team sports such as football, rugby, and basketball consistently shows that targeted pyometric and resistance training enhances key physical capacities in youth athletes--namely sprint velocity, maximal strength, and change-in-direction performance [108; 109; 110]. These improvements are particularly notable when training programs are adapted to the athlete's biological maturity, with pyometric methods proving especially effective prior to peak height velocity and combined modalities yielding greater benefits in post-peak heigh velocity stages [111]. In contrast, the literature on youth handball reflects a delayed and inconsistent incorporation of these principles. While developmental models such as the Long-Term Athlete Development (LTAD) framework and the Youth Physical Development Model have been formally integrated into the physical preparation systems of rugby and football federations [112; 113], handball research continues to lack unified criteria for training periodization and load progression. Some recent contributions in handball have explored performance diagnostics and proposed multidimensional evaluation tools [114], yet these remain disconnected from broader developmental planning.