Comparison of kinetic and kinematic variables during single-leg jump landing between athletes with and without concurrent flexible flatfoot and genu varum deformities

Jumping and landing are among the most important movements in most sports; however, athletes with flexible flatfoot or genu varum deformities are vulnerable to lower limb injuries during these maneuvers. Therefore, this study aimed to compare the kinetics and kinematics of single-leg jump-landing between athletes with and without concurrent flexible flatfoot and genu varum deformities. The study was a comparative observational study that included athletes with ( N = 10) and without ( N = 10) concurrent flexible flatfoot and genu varum. Flatfoot and genu varum were confirmed by a physiotherapist using Brody’s method and Caliper technique. Jump-landing kinematics and joint torques were measured using 3D motion capture (Motion Analysis, Santa Rosa, USA) and a force plate (Bertec Corporation, Columbus). Groups were compared using independent t-tests and Mann-Whitney U tests, and significance was accepted at p < 0.05. The findings revealed significant differences between the two groups in the torque of the ankle and knee joints in the frontal and horizontal planes at initial foot contact ( P < 0.001). At maximum knee flexion, significant differences were observed in the ankle joint (frontal and horizontal planes, P < 0.001), the knee joint (frontal plane, P < 0.001), and the hip joint (frontal and horizontal planes, P < 0.001 and P < 0.015, respectively). Additionally, significant differences were found in the torque of the ankle joint in the sagittal ( P < 0.036) and frontal planes ( P < 0.001). The present study showed that individuals with and without concurrent flexible flatfoot and genu varum deformities exhibit different responses in the lower limbs during the single-leg jump-landing task. Future studies should investigate whether interventions such as foot orthoses or other corrective strategies can modify landing mechanics and potentially reduce cumulative joint loading, thereby informing evidence-based recommendations for athletic populations.