## 4 Discussion
### Knee ROM  
A previous study indicated a strong correlation between the ROM of the knee flexors in football players before matches and the incidence of muscle strain in related muscle groups. Athletes who sustained injuries during matches had approximately 3\({}^{\circ}\) less knee flexion ROM before the game compared to those who remained uninjured [32]. In our study, we observed a 4.8\({}^{\circ}\) reduction in right knee flexion ROM in the injured participants, implying that they might be at increased risk of injury. Our review of studies on the relationship between ankle injuries and passive knee flexion ROM reveals inconsistent findings. [PERSON] and associates reported an association between reduced knee flexion and chronic ankle instability [19]. Conversely, other studies have found no relationship between chronic ankle instability and reduced knee flexion [33; 34]. In our study, a significant difference in right passive knee flexion ROM was observed when comparing the injury and non-injury groups. This finding aligns with the conclusions of [PERSON] and associates, which reported that restricted ankle mobility is associated with reduced hip and knee flexion during landing [19]. From a biomechanical perspective, the soccer kicking motion requires coordinated force generation across lower limb joints, including the knee and ankle. During the back-swing phase, the knee flexes (at an angular velocity of 745-860 deg\(\cdot\)s\({}^{-1}\)) and internally rotates, while the ankle progressively reaches its maximum plantarflexion angle (at an angular velocity of 860 deg\(\cdot\)s\({}^{-1}\)) [35]. During the forward motion phase, the knee extends while externally rotating until it reaches its maximum extension velocity (860-1720 deg\(\cdot\)s\({}^{-1}\)). Simultaneously, the ankle remains adducted and plantarflexed [36]. Meanwhile, a previous study indicated that athletes compensate for restricted ankle mobility by reducing the entire lower limb flexion range, including knee and hip flexion [19]. Additionally, individuals with chronic ankle instability exhibit deficits in knee and hip muscle strength. This suggests that after an ankle injury, knee flexion movement may be impaired, as the weakened knee and hip muscle strength can affect knee stability and movement control [37]  
[PERSON] and associates suggest that excessive ankle inversion is considered a risk factor for ACL injury, directly correlating with ACL tears [38]. They point out that prolonged inversion of the ankle can lead to excessive internal rotation and anterior displacement of the tibia and, thus, may produce a preloading effect on the ACL. If the integrity of the ACL is compromised, it may further result in subluxation. Also, in a study by [PERSON] and associates, an association between excessive ankle inversion and ACL injuries was also observed in other sports, including gymnastics, American football, and basketball, with athletes in the ACL injury group showing greater degrees of ankle inversion [39]. They pointed out that in football players, the nuclear drop value in the ACL-injured group (8.4 \(\pm\) 4.2 mm) was greater than that in the non-injured group (5.9 \(\pm\) 2.4 mm). This value was significantly higher than the navicular drops values in gymnastics and basketball players, which were 5.0 \(\pm\) 2.5 mm in the ACL-injured group and 3.0 \(\pm\) 1.1 mm in the non-injured group. Soccer is also one of the sports with the highest risks of ACL injuries. In collegiate soccer, the ACL injury rate for female athletes was 0.32, while for male athletes, it was 0.12. These rates are higher than those observed in collegiate basketball, where the injury rates were 0.29 for female athletes and 0.08 for male athletes [40]. The higher probability of ankle inversion and ACL injuries in soccer players might be related to the frequent cutting and change-in-direction movements. During rapid direction changes, the body's center of mass shifts quickly, causing the ankle to bear significant lateral forces.