Association between preparatory muscle activation and peak valgus knee angle

Valgus knee angle (VKA) maybe a predictor of non-contact anterior cruciate ligament (ACL) injuries. Pre-programmed muscle activation strategies may exist which could contribute to the larger VKA displayed in women compared to men. The current study examined the relationship between the peak VKA and preparatory muscle activity. Twenty-one adults were asked to perform five trials of a forward hop. Lower extremity kinematics and surface EMG were recorded. Peak VKA and EMG from 100 ms prior to ground contact were used in the data analyses. Three multiple linear regressions, where muscle activity was regressed upon the peak VKA, were run using subsets (female, male, and male/female) of the sample. Partial regression coefficients were considered significant at P ⩽ 0.05. When female subjects were exclusively included in the model, a higher peak VKA was associated with increased preparatory vastus lateralis and lateral hamstring activity, while a lower VKA was associated with increased preparatory vastus medialis activity (P ⩽ 0.05). When both genders and males alone were considered, preparatory activity was not associated with peak VKA (P ⩾ 0.05). Neuromuscular training promoting equal preparatory muscle activity in the medial-to-lateral quadriceps and hamstrings may reduce the incidence of ACL injuries in females.