## 4 Discussion
Very few studies have examined the factors influencing on-field, in-game physical performance in soccer players. One study found significant correlations between changes in body composition and on-field, in-game performance outcomes [50]. Specifically, a reduction in body fat percentage and an increase in fat-free mass were linked to improved squat and bench press performance [50]. Another study reported significant differences in body composition metrics, such as fat mass and fat-free mass, between elite and non-elite young soccer players [51]. Elite players had lower fat mass and higher fat-free mass, which were associated with better performance in physical tests, such as the 15-m sprint, repeated-sprint ability, and countermovement jumps [51]. However, physical tests like sprints do not always directly translate to higher on-field, in-game performance or competitive success [13; 17; 32; 33; 34]. Players who excel in these tests do not necessarily perform better in games [13; 17; 32; 33; 34]. Research suggests that high-intensity running distance during games is related to players' aerobic capacity, vastus lateralis thickness, and vastus lateralis pennation angle in the dominant leg (R = 0.989, SEE = 115.5 m, \(p\) = 0.001) [31]. Muscle architecture may be a key predictor of on-field, in-game physical performance in female college soccer players [31; 47]. Thus, body composition measurements can provide valuable insights into soccer players' on-field, in-game physical performance. While we found significant correlations between body composition and on-field, in-game performance metrics, other factors may also influence performance. These factors include overall fitness, technical and cognitive skills, psychological traits, tactical changes, match location, and match status, all of which can impact both body composition and performance. In our study, all participants were starters who consistently played full matches and followed a standardized training program that included endurance and strength sessions. Despite this, there was variability in overall fitness among the players. In addition to fitness, high-level soccer players must possess advanced technical and cognitive skills and may exhibit distinct physiological attributes [52]. Psychological traits, such as hope for success, task orientation, self-optimization, and self-efficacy, have been shown to influence recruitment in competitive academies [53]. Although no studies have directly examined the relationship between psychological factors and on-field, in-game physical performance, these factors are likely crucial. External influences such as the quality of the opponent, match location, and match status can also affect performance. Research shows that players tend to cover more distance and engage in more high-intensity running against higher-ranked opponents due to increased physical and tactical demands [6; 54]. Similarly, players perform more high-intensity running when their team is winning compared to when they are losing, likely due to differing tactical strategies [6; 55]. Additionally, match location can impact performance, as playing at home may provide psychological advantages, while away games can introduce unfamiliar environmental factors [6]. These external factors underscore the need to assess on-field, in-game performance across multiple games or an entire season to account for these variations and gain a more comprehensive understanding of player and team performance [6]. We did not find any significant relationships between total-body or lower-extremities lean mass and on-field, in-game physical performance. While DXA provides a precise estimation of total and regional lean mass distribution, it does not assess muscle quality or muscle fiber type. Specific muscle characteristics, such as muscle fiber composition, may influence aerobic and anaerobic capacities. Endurance athletes, for example, tend to have a higher proportion of slow-twitch fibers compared to athletes in sports that require speed, agility, and power [56].