Association among isometric hip strength, hip joint stiffness, and dynamic Knee Valgus in jump-landing tasks.

Dynamic hip joint stiffness has been linked to lower extremity biomechanics, especially in high-velocity movement tasks, including jump-landing, which exposes the athlete to a higher risk for injury. Whether hip muscles' isometric strength correlated with dynamic hip joint stiffness, as well as dynamic Knee Valgus (DKV) related kinematics parameters, is unclear. Twenty male recreational athletes aged 18 to 24 years completed the Double-legged drop vertical jump (DLDVJ) and Single-legged drop vertical jump (SLDVJ) tasks. At the same time, lower extremity kinematics and dynamic hip and leg stiffness during the eccentric phase of the landing tasks were measured for each trial with 3-dimensional motion and force plate. The isometric hip muscles' strength was also measured using a hand-held dynamometer. A correlation matrix test was used to determine the relationship among the isometric hip muscles' strength, dynamic hip joint stiffness, and DKV-related kinematics parameters. The findings revealed that a reduction in hip stiffness in the frontal plane correlates with increased hip internal rotation during the eccentric phase of both the DLDVJ (p = 0.005; r = - 0.603) and SLDVJ (p = 0.048; r = - 0.447) tasks. Furthermore, increased isometric hip adduction to abduction strength ratio is linked to increased hip internal rotation at both the initial contact (DLDVJ: p = 0.001; r = 0.579; SLDVJ: p = 0.002; r = 0.647) and the eccentric phase (DLDVJ: p = 0.047; r = 0.449; SLDVJ: p = 0.007; r = 0.586]) of these tasks (p < 0.05). A positive relationship was also observed between the isometric hip external to internal rotator strength ratio and hip stiffness in the frontal plane during the SLDVJ (p = 0.012; r = 0.550). However, that was not the case with the DLDVJ task. The observation of DKV movement fault during screening is associated with decreased hip stiffness in the frontal plane and an imbalance in the isometric hip adduction to abduction strength ratio, which should be considered and applied in assessments and design of training interventions. Additionally, the authors attributed the significant difference observed between the two movement tasks regarding the correlation between the isometric hip external to internal rotator strength ratio and dynamic hip stiffness in the frontal plane to each task's inherent varying physical demands.