Knee Joint Biomechanics During Lunges at Different Tibial Angles and External Loads: A Musculoskeletal Analysis with Finite Element Insights

<jats:p>Objective: This study investigates knee joint biomechanics during lunges under varying tibial angles and external loads using musculoskeletal modeling and finite element analysis. The goal is to provide a biomechanical basis for understanding knee loading patterns and optimizing sports training and rehabilitation. Methods: Twenty-six healthy young men performed lunges under tibial inclination angles relative to the ground (60 degrees and 90 degrees) and two external load conditions (bodyweight and an additional 98 N external load). Kinematic and kinetic data were captured using motion capture and force plates. Musculoskeletal models were used to estimate joint moments, range of motion, and stiffness, with data analyzed using two-way repeated-measures ANOVA. Finite element analysis was performed at 90 degrees tibial angle to evaluate tissue stress and displacement. Results: The joint moment at a 60 degrees tibial angle was much higher than at a 90 degrees. External load showed significant effects on knee stiffness, with lower rotational stiffness in the horizontal plane (P &lt; 0.001) and lower coronal plane stiffness at 90 degrees (P = 0.012) under the 98 N external-load condition, indicating reduced resistance to angular displacement in these planes. Under the 90 degrees tibial-angle condition with external load, peak stress and displacement were concentrated in the posterior horn of the meniscus, with a maximum displacement of 3.12 mm. Conclusion: The anterior tilt of the tibia increased sagittal-plane knee loading, while external load mainly reduced joint stiffness in the coronal and horizontal planes. Under the 90 degrees loaded condition, the concentration of stress and displacement in the posterior horn of the meniscus suggests a mechanically unfavorable loading pattern rather than direct evidence of injury risk. These findings may provide useful biomechanical information for load management during lunge-based training and rehabilitation.</jats:p>