The principle of "Kicking with the Left Heel" in Chen-style Tai Chi Chuan based on sports biomechanics experiments

Objective Recent research on Tai Chi Chuan has focused on its fitness and chronic disease intervention effects. Few studies have explored the martial techniques that embody numerous Tai Chi principles. This study assessed the "Kicking with the Left Heel" movement from traditional Chen-style Tai Chi Chuan to provide a scientific basis for understanding its underlying principles. Method The study enlisted 12 high-level Tai Chi Chuan athletes, including six national master-class athletes, two first-class athletes, and four second-class athletes, divided into elite (national master-class) and excellent (national first/second-class) groups. A three-dimensional motion capture system and force platform were synchronized to measure the kinematic and kinetic data of the lower limbs during the movement. The data were processed using Visual3D to obtain human biomechanical indices. The differences were analyzed using independent sample t-tests. Results (1) The elite group exhibited a shorter knee extension phase duration than the excellent group ( P  < 0.05). The elite group exhibited greater maximum and minimum displacements of the center of mass in the anterior-posterior direction, but less maximum and minimum displacements in the left-right and up-down directions ( P  < 0.05). (2) At the moment of maximum knee flexion, the left kicking limb showed in the sagittal plane that the hip joint of the elite group had a greater flexion angle than that of the excellent group ( P  < 0.05); the ankle presented a smaller plantar flexion angle ( P  < 0.05). In the coronal plane, the ankle in the elite group was more inverted, while it was slightly everted in the excellent group ( P  < 0.05). At the point of maximum knee extension, the hip joint in the sagittal plane of the elite group was more flexed compared to the excellent group, which presented a slightly extended hip ( P  < 0.05). In the coronal plane, the elite group had smaller hip abduction and ankle eversion angles than the excellent group ( P  < 0.05). (3) At the point of maximum knee extension, the left kicking limb for the elite group exhibited hip extension angular velocity in the sagittal plane. In contrast, the excellent group displayed hip flexion angular velocity ( P  < 0.05). In the horizontal plane, the knee demonstrated internal rotation angular velocity in the elite group and external rotation angular velocity in the excellent group ( P  < 0.05). (4) The left kicking limb of the elite group exhibited greater maximum velocities of the center of mass in all three segments compared to the excellent group ( P  < 0.05). Moreover, during maximum knee flexion and extension, the center of mass velocities in these three segments were consistently higher in the elite group compared to the excellent group ( P  < 0.01). (5) At the point of maximum knee flexion and knee extension, there were no statistically significant differences in the vertical ground reaction forces between the two groups ( P  > 0.05). Conclusion The elite group surpassed the excellent group at the athletic level and conformed better to the mechanical principles of the "Kicking with the Left Heel" movement. The critical factors in executing the movement included stability, speed, stopping, overlaying, and efficiency that fully demonstrated the principles of Chen-style Tai Chi Chuan, integrated rigidity and flexibility, alternated between speed and slowness, and featured elastic explosive strength and interconnected movements.