# Profiling of Physical Qualities of Highly Trained Portuguese Youth Soccer Players
## 4 Discussion
Faster sprint speeds are associated with greater ground reaction forces [36], which faster players present as superior rapid force capacity. Indeed, players from higher age categories presented superior explosive force performance. This can also be attributed to the distinct maturational status of players since different maturational stages lead to specific physiological and structural changes [37; 38; 39]. Similar results were reported in two top-level Brazilian clubs in which senior and U20 players presented higher speeds in a linear 20 m sprint compared to U17 and U15 players [40]; significant age-related differences were observed in sprint performance among young soccer players as well [41]. Contrary to our initial hypothesis, no differences were found between playing positions, with previous studies reporting contrasting findings [1; 42; 43; 44; 45; 46]. For example, greater sprint performance in forwards compared to defenders was observed across different sprint distances (5 m, 10 m, 20 m, and 30 m) [42; 43]. On the other hand, no differences in 10 m and 30 m sprints between playing positions were reported [44; 45; 46]. Authors suggested that approaching the professional level at higher age categories, positional differences occur with forwards becoming the fastest players of the team [47]. One possible explanation could be due to modern soccer's increasing emphasis on outfield players contributing to overall play, leading to more uniform physical performance across positions [48]. Moreover, a recent study reported no significant differences in sprint performance, knee flexor force capacity, and mechanical properties of the hannstrings between playing positions in players from different competition levels [1]. This finding suggests that such a phenomenon is not exclusive to youth development but also persists in senior competition contexts. Regarding correlation between tests, a significantly stronger correlation was verified between the CMJ and SJ (\(r=0.86\); \(p<0.001\)) due to similarities between the two tests since players applied vertical force on the ground (i.e., vertical force vector). The IMTP also revealed a moderate correlation with explosive jumping and sprinting. Previous studies demonstrated a moderate-to-strong correlation between the IMTP and sprint (\(r=-0.69\); \(p\leq 0.01\)) and jumping performance (\(r=0.81\); \(p\leq 0.01\)), respectively [49; 50]. Although stronger players tend to perform better in jumping and sprint performance tests, the moderate correlations found suggest that other factors besides peak torque are determinant for jumping and sprint performance such as neuromuscular coordination and rapid force development [51]. Both the CMJ and SJ were moderately correlated (\(r=0.60\); \(p<0.001\)) with the BJ. Although these tests encompass a squatting pattern, the SJ and CMJ are essentially vertical-oriented while the BJ has a horizontal force component mediating jump performance [52]. Sprinting and jumping can be categorized as explosive movements. The results of the present study indicated that jumping tests were moderately correlated with sprint performance (\(r=0.37\)-\(0.42\); \(p<0.001\)). However, sprinting and jumping performance present kinetic and kinematic differences due to reliance on distinct attributes. A previous systematic review and meta-analysis demonstrated moderate-to-strong correlations (\(r=0.45\)-\(0.73\); \(p<0.001\)) between standing long jump distance and acceleration (0-30 m) and maximal sprint (30-100 m), respectively [53]. Moreover, moderate correlations were reported between the SJ (\(r=0.56\); \(p<0.05\)) and CMJ (\(r=0.55\); \(p<0.05\)) and sprint [54]. In fact, sprinting is associated with a capacity to generate higher ground force reactions, with a specific orientation, in minimal contact times [55], whereas jumps involving a horizontal force vector component (e.g., BJ) are characterized by higher ground contact times, which influences the magnitude of correlations.