## 4 Discussion  
The aim of this study was to describe and compare the kinematic demands of the Spanish women's national football teams in the U-17, U-20, and senior categories during their respective FIFA World Cup participations. Significant differences were found across several performance variables between categories. The main findings were: (1) Significant differences were observed between the senior team and both U-17 and U-20 in all variables, except TD, where no difference appeared between senior and U-20. TD also differed significantly between U-17 and U-20. (2) TD, HSR, and sprint distances were greater in the senior category compared to U-17 across all positions, except for CM in sprint distance. Differences between senior and U-20 were noted in HSR for CB, FB, and CM, and in sprint for CB and FB. (3) Accelerations were significantly higher in the senior group than in both U-17 and U-20 across all positions. (4) For decelerations, significant differences emerged between senior and U-17 across all positions except WG, and between senior and U-20 in CM and FB. (5) HMLD differed significantly across all positions between senior and both U-17 and U-20. The analysis of distance-related variables showed that senior players recorded higher TD, HSR, sprint, and HMLD values than U-20 and U-17 players. This pattern aligns with previous studies reporting greater locomotor demands in elite senior players compared to younger counterparts [4; 5; 16; 17; 18]. This progressive rise from U-17 to senior levels may suggest improved physical performance associated with biological maturation, potentially influenced not only by physiological or structural factors, but also by an increase in match tempo, reflecting enhanced technical-tactical demands at higher levels of competition [17; 19]. Notably, differences between categories increased with variable intensity. Seniors covered 4% and 16% more TD than U-20 and U-17, respectively; 30% and 40% more HSR; and 32% and 47% more sprint distance. This trend highlights the need for age-specific training interventions that progressively enhance physical capacities in accordance with the escalating technical-tactical and physiological demands of elite competition. Regarding position-specific physical demands, patterns in distance covered were similar across all categories. In terms of TD, CM covered the greatest distances, followed by FB, while attacking players (WG and ST) covered less. On the one hand, despite covering less total distance, ST exhibited higher physical demands in HSR, HMLD, and sprint distance, ranking among the positions with the highest values in these variables. This pattern suggests that while ST performs less overall movement, the intensity of their efforts is substantially higher. On the other hand, FB appeared to have the greatest kinematic demands. Across all variables, players in this position covered the highest distances, indicating the need for a high level of physical conditioning to meet the demands of match play, as highlighted in previous studies [14; 20]. Therefore, teams' staff during international competitions should make informed decisions about the types of training drills to implement, depending on whether the physical objective is to replicate match demands or to reduce exposure to high-intensity efforts during congested competitive periods [21]. In the latter case, moderating physical loads may be essential to promote adequate recovery and maintain performance capacity across successive matches. The inclusion of HMLD in this study adds valuable information, as it reflects sustained physical effort and metabolic demands beyond speed thresholds, making it a strong indicator of overall physical load during matches [13; 14]. In our study, senior players covered 53% and 58% more distance than U20 and U17 players, respectively. The differences between senior players and their U20 and U17 counterparts were notably significant, as senior players doubled the distance covered at high metabolic load.