## 4 Discussion
Competitive soccer requires both large aerobic endurance and the ability to perform short, intense bouts of anaerobic activity. To our knowledge, only one study has measured muscle characteristics of the vastus lateralis in soccer players [57]. The relationship between muscle characteristics and on-field, in-game physical performance has not yet been established. Muscle fiber type may influence an athlete's ability to perform both short-term intense running and long-distance efforts, which could explain why we did not find a significant relationship between lean mass and on-field, in-game performance. While our findings suggest that reducing body fat can enhance performance at moderate and high intensities, it is crucial to adopt a holistic approach that considers the trade-offs involved in targeting body composition changes. Focusing solely on fat reduction without adequate attention to lean mass preservation, recovery, and overall health may result in unintended consequences such as muscle loss, increased injury risk, and diminished recovery capacity. Adhering to the principle of specificity and incorporating tailored nutritional strategies is essential for optimizing both performance and body composition. Additionally, body composition should be carefully monitored, especially in female athletes, as drastic changes can impact not only physical performance but also mental health and overall well-being. Excessive focus on body composition in female athletes may lead to issues such as disordered eating, menstrual dysfunction, and long-term health consequences. For a comprehensive review of how to address body composition in female athletes, [PERSON] et al. (2024) provide an excellent analysis of the interplay between dietary practices, body composition, and sports performance, offering valuable insights and recommendations [58]. To our knowledge, this is the first study to assess the relationship between body composition and direct measurements of on-field, in-game physical performance in soccer players. Future research should begin by increasing the sample size through the inclusion of players from multiple teams, which would improve the generalizability of findings and allow for comparisons across different team environments and playing styles. Expanding the scope to include players in various positions (defenders, midfielders, attackers) could also provide valuable insights into how total and regional body composition correlates with on-field, in-game performance, as these factors can vary significantly by position [9; 34; 59]. Moreover, longitudinal studies tracking body composition changes across a single season or multiple seasons would be particularly useful in understanding how fluctuations in fat and lean mass correlate with performance. Measuring body composition at multiple points during the season would clarify the effects of fatigue, recovery, and training load on performance over time. Further research should explore muscle characteristics and psychological factors--such as mental fatigue, motivation, and resilience--that likely affect performance, particularly in the second half of games. Investigating these psychological aspects alongside physical metrics would offer a more comprehensive view of performance determinants. Finally, examining training regimens that optimize both physical and psychological factors could further improve our understanding of performance outcomes and provide practical strategies for enhancing player development and on-field, in-game performance.