## 4 Discussion  
This study aimed to assess and compare the physical development components of professional soccer players competing at different levels. No significant statistical differences between elite and non-elite players were seen in body composition parameters. However, elite players performed significantly better in static strength (handgrip), lower-body explosive strength (CMJ and SJ), flexibility (sit and reach), and balance tests, even after adjusting for the effects of CA. In a study comparing anthropometric and body composition variables between players from the Serbian premier league and the fifth Serbian league, the authors found that elite players were significantly heavier and had a lower BF% than non-elite players [26]. However, in line with our findings, another study conducted on 132 male professional soccer players found that there were no significant differences in height, body mass, and BF% between players from Division 1 and Division 2 [27], even though players from Division 1 were taller, heavier, and presented a lower BF% than players from Division 2. It is essential to clarify that BF% has been negatively correlated with physical development test performance in previous research [28; 29; 2], especially for tests which require full-body movement such as vertical jumping, sprinting, and change of direction. In this study, although body composition parameters were not different between elite and non-elite players, it is essential to underline the importance of monitoring body composition during the season to achieve better physical development levels. In our results, elite players showed substantially better scores in static strength than non-elite players. The mean score of the EG was almost 18% higher (approximately 9 cm) than that of the NEG with the lowest score (NEG-B). A previous study which aimed to compare the handgrip performance of a group of amateur soccer players and a group of healthy adults concluded that soccer players attained larger mean values in handgrip than the control group (+5.6 kg, \(p\leq\) 0.01) [30]. Indeed, these results would be expected due to the systematic training that amateur soccer players are submitted to. Across several sports contexts, elite players have shown significantly better scores on the handgrip performance than their non-elite peers [8], which is in line with our findings. Handgrip is an isometric strength measure described as a strong predictor of absolute strength [31; 32] that coaches may consider in the training process of non-elite players. Meanwhile, the mean score of the EG was approximately 17% better for the CMJ performance (nearly 7 cm) and 16% better for the SJ performance (almost 6 cm) than that of the NEG with the lowest score (NEG-B), even after adjusting for the effects of CA. These results would be expected since lower-body explosive strength has been consistently related to game performance, particularly to high-intensity actions such as sprinting and changing direction, which have been described as the most decisive actions preceding goals [7; 9]. Thus, since speed and agility capacities are crucial for elite soccer players, higher levels of lower-body explosive strength were expected to be observed in this population. According to the literature, lower-body strength strongly predicts speed and agility [28; 33]. Past research among 25 male professional soccer players aged 25.1 \(\pm\) 4.6 years reported that increased lower-body strength was strongly correlated with faster 30 m linear sprint times (r = \(-\)0.57, \(p\leq\) 0.01) and a greater CMJ height (r = 0.39, \(p\leq\) 0.05) [33]. In another sample of junior male soccer players aged 17.0 \(\pm\) 0.5 years, the SJ was described as a strong predictor of acceleration and 5 m linear sprint time [34]. In summary, the results of this study, combined with past findings, may raise awareness regarding strength development as part of the soccer training process and as a crucial tool to enhance game performance.