Beyond muscle activation: the role of biomechanical properties of muscles in determining dynamic knee valgus in female volleyball players

Dynamic knee valgus (DKV) is considered a risk factor for knee injuries, particularly in female athletes. Muscle activation and biomechanical properties are thought to play a role in its development, yet their exact contributions remain unclear. This study aimed to investigate the biomechanical properties and electromyographic activity of lower extremity muscles in female volleyball players with and without DKV. Thirty-six female volleyball athletes aged 12–18 were allocated to DKV (n = 18) and control (n = 18) groups based on single-leg squat test. Biomechanical properties (muscle tone, elasticity, stiffness) of the muscles were measured using MyotonPro®. Surface electromyography was used to assess muscle activation and onset times of the gluteus medius (GM), adductor magnus (AM), vastus medialis (VM), vastus lateralis (VL), semimembranosus (HM), and biceps femoris (HL) during landing phase of the volleyball spike. There were no significant demographic or sport-specific differences between the groups. VM/VL and HM/HL muscle tone ratios and AM/GM, VM/VL and HM/HL stiffness ratios were significantly higher in DKV group (p < 0.05). DKV group showed significantly lower activation in GM and HL and higher AM/GM and HM/HL ratios (p = 0.001 and p = 0.015). GM-AM onset time difference was significantly lower in DKV group (p < 0.001). Multiple linear regression analysis did not reveal any statistically significant predictors of knee valgus angle during the landing phase of the spike. The tone and stiffness ratios of the medial thigh muscles to the lateral ones (AM/GM and HM/HL) were increased. Activation of GM and HL muscles were decreased in athletes with DKV. Since neither biomechanical properties nor muscle activation affected frontal knee valgus angle during the spike, it is speculated that the change may reflect a musculoskeletal adaptation.