Correlation between dynamic knee valgus and quadriceps activation time in female athletes

Objectives: The risk for female athletes suffering an anterior cruciate ligament injury is 3.5 times more than males. The high rate of anterior cruciate ligament injuries in females compared to males appears to be due to worse neuromuscular control strategies. The unbalanced ratio between the medial and lateral quadriceps and the dynamic valgus knee contribute to increasing the risk of the lesion to the anterior cruciate ligament. This study aims to evaluate the correlation between the increased dynamic valgus knee and the reduction of the mediolateral quadriceps ratio in recruitment and timing during a movement that puts the anterior cruciate ligament under stress. Methods: We enrolled sixty athletes (30 males and 30 females): professional dancers, soccer, and volleyball players. To put stress on the anterior cruciate, the athlete falls with one leg from a 32 cm platform. Four surface EMG probes determined the rectus femoris (RF), vastus medialis (VM), semitendinosus (ST), and biceps femoris (BF) activation time. An inertial motion sensor connected to the probes can quantify the preactivation time of the muscles. An open-source video post-production software (Kinovea) defined the angle dynamic valgus knee. Results: female athletes showed a delayed mediolateral quadriceps activation and wider dynamic valgus knee angles compared to males. Pearson's r test (t = 9.8, df = 58, p<0.05) showed a significant correlation of 0.79. Conclusions: These results seem to suggest a linear correlation between late activation of the vastus medialis recorded in women and the dynamic angles of the valgus. These findings confirm the need for training programs that increase neuromuscular control strategies.