The Effect of Muscles Fatigue on the Knee’s Kinetics and Kinematics Characteristics

Badminton is very popular on college campuses. In badminton, the anterior cruciate ligament of the players has a higher risk of injury. There are many studies investigating the impact of fatigue on the injury of professional athletes, but few studies focused on college students. We hypothesized that the knee joint would experience greater ground reaction forces, valgus moments, and flexion moments of lunge contact in amateur after fatigue than those indicators before fatigue. Ten male badminton amateurs were enrolled in this study. They performed a lunge to hit the shuttlecock at the designated position and then quickly returned to the starting position before and after fatigue. Fatigue was induced by repeated isokinetic flexion/extension of the knee. Lower body kinematics and ground reaction force (GRF) were collected and further used to calculate the lower body joint moments from initial contact to maximum knee flexion. Compared to the pre-fatigue condition, the peak flexion moment ( p = 0.012) and peak abduction moment of knee joint ( p = 0.01), and maximum horizontal ground reaction force ( p = 0.027) increased significantly at the initial contact ( p = 0.01). After muscle fatigue, the knee buckling moment and valgus moment increased significantly at initial contact, and the horizontal backward maximum GRF also increased significantly. These changes might increase the injury risk of anterior cruciate ligament (ACL). The fatigue of the muscles around the knee joint did not change the maximum GRF in the vertical direction at the moment of contact. Combined with the results of our study, badminton coaches and teachers should increase the training of lower extremity muscle strength and endurance in our daily class and training, and also should pay special attention to the coordinated development of muscles.