Evaluation of myoelectric activities and biomechanical properties of muscles associated with dynamic knee valgus in female volleyball athletes

Aim: To investigate the electromyographic (EMG) activities and biomechanical properties of lower extremity muscles associated with dynamic knee valgus (DKV) in female volleyball athletes with and without DKV. Materials and Method: Between February and May 2024, female volleyball players aged 12-18 who met the inclusion criteria were allocated to DKV (n=18) and control groups (n=18) based on single-leg squat test positivity. During the landing phase of the volleyball smush, the activation and activation onset times of the gluteus medius (GMed), adductor magnus (AddM), vastus medialis (VM), vastus lateralis (VL), hamstring medialis (HM), and hamstring lateralis (HL) muscles were evaluated using surface EMG. Biomechanical evaluations (tone, elasticity and stiffness) of the same muscles were performed with MyotonPro®. Results: No significant differences were detected between the groups in terms of sociodemographic and sport-specific data (p>0.05), except DKV angles (p=0.045). The activation of the GMed and HL muscles were significantly lower, while AddM/GMed and HM/HL values were significantly higher (p=0.001 and p=0.015, respectively) in the DKV group. The difference between GMed and AddM onset times was significantly lower in the DKV group (p<0.001). The cut-off value for the DKV angle during the volleyball smush was determined as 12.05 through ROC analysis. Analysis based on this value showed that the difference between onset times of GMed-AddM was a significant risk factor for DKV, with each unit (ms) decrease in this time increasing the risk by 1.5%. Analysis of biomechanical values showed that the tone ratios of VM/VL and HM/HL and the stiffness ratios of AddM/GMed, VM/VL, and HM/HL were higher in DKV group (p<0.05). Conclusion: The activation of GMed and HL muscles were decreased in athletes with DKV. The difference between GMed-AddM onset times decreased and this difference was identified as a significant risk factor for DKV. The tone and stiffness ratios of the medial thigh muscles to the lateral ones were increased. Keywords: Dynamic knee valgus, Electromyography, Muscle activity, Volleyball