Phase-dependent loading characteristics of the supporting-side knee joint during the flying kick with a 180-degree inward turn in competitive Tai Chi

Introduction Competitive Tai Chi has increasingly incorporated high-difficulty aerial and single-leg landing techniques. The flying kick with a 180° inward turn (322C) is a demanding C-level movement that requires rapid take-off, aerial hand-foot slap, body rotation, and stable single-leg landing. However, the phase-dependent loading characteristics of the supporting-side knee joint during this movement remain unclear. Methods Ten male competitive Tai Chi athletes performed the 322C while three-dimensional kinematics and ground reaction forces (GRF) were recorded. The movement was divided into four phases: take-off propulsion (P1), hand-foot slap (P2), flight end (P3), and landing cushioning (P4). Joint angles, moments, reaction forces, and vertical GRF (VGRF) were calculated using inverse dynamics. A subject-specific finite element (FE) model of the supporting-side knee was reconstructed from CT and MRI, and the peak landing loads were applied to evaluate internal tissue stresses. Results P4 had the longest duration (1.639 s). VGRF reached 5.18 ± 1.84 body weight (BW), with a peak knee extension moment of 5.01 ± 1.64 N.m-kg −1 and a peak compressive joint reaction force of 22.58 BW. FE analysis showed non-uniform stress distributions, with the highest von Mises stress observed in the anterior cruciate ligament (ACL; 54.24 MPa), posterior cruciate ligament (41.79 MPa), medial meniscus (23.53 MPa), and lateral femoral cartilage (9.62 MPa). Discussion The 322C imposes different mechanical demands on the supporting-side knee across phases. P1 is mainly characterized by rapid knee extension and load transfer, whereas P4 involves high impact, axial compression, shear, and rotational stabilization. The stress concentrations observed in the ACL and anterior regions of the menisci indicate areas of relatively high local loading during the movement. These findings provide biomechanical information for understanding knee loading during the 322C and may help inform technique optimization and injury-prevention strategies in competitive Tai Chi.