Effect of Functional Fatigue on Dynamic Knee Valgus in Adult Football Players

Dynamic knee valgus is a significant risk factor for anterior cruciate ligament (ACL) injuries. Functional fatigue is believed to alter movement patterns. Therefore, this study aimed to investigate the impact of functional fatigue on dynamic knee valgus angle in Football players. Twenty-two adult male football players with a 5-hour average training per week and a pre-existing dynamic knee valgus angle less than 12 degrees participated in this study. Dynamic knee valgus was measured during a single-leg landing task from a 35 cm box using a 2D video analysis system. The kinematic data were analyzed using Kinovea software. After a baseline measurement, participants played a 90-minute football match. Perceived exertion rate was assessed using the Borg Rating of Perceived Exertion scale. Participants were considered fatigued if they scored 15 or above. Post-fatigue, the landing task was repeated. Paired t-tests were used to compare pre- and post-fatigue knee valgus angles. Results showed a significant increase in dynamic knee valgus angle after the match (p = 0.021), indicating that functional fatigue exacerbates knee valgus. The average increase in knee valgus angle was 4.039 degrees. Functional fatigue from a 90-minute football match can significantly increase dynamic knee valgus in football players with pre-existing valgus, potentially increasing the risk of ACL injuries. It is suggested that football players focus on the strength and endurance training targeting knee supporting muscles in fatigues conditions during pre-season and in-season trainings to minimize the injuries.