Mechanism of Bafa Wubu of Tai Chi Promoting Lower Extremity Exercise: A Cross-sectional Study Based on an AnyBody Musculoskeletal Model
Authors: li haojie , Ji Zhongqiu , Lyu Shaojun , Peng Fang , Li Xiongfeng , Guo DanDanielle , Shen Shunze 
Published: April 2022

Abstract
Background: This paper aimed to explore the scientific training methods and technical characteristics of Bafa Wubu, as well as its contribution to comprehensive exercise of the lower extremities, by analyzing the biomechanical characteristics of the lower extremities of participants who practice Bafa Wubu at different levels and by comparing their femur loading during Bafa Wubu and walking. Methods: A total of 16 male participants were recruited and divided into an amateur group (N=8) and a professional group (N=8).Data were collected by a BTS 3D infrared-based motion capture system, Kistler 3D force plate and BTS surface electromyography. The kinematic and kinetic parameters of the lower extremities were captured by AnyBody 7.2 simulation modeling and finite element analysis of the femur was performed with an ANSYS 19.2 workbench.Results: During Elbowing and leaning sideways with steps sideways (ELS), the ground reaction force of the professional group was significantly higher than that of the amateur group in the sagittal, vertical and frontal axes (P<0.01). During six sets of motions (except Standing knee raises:SKR), the knee flexion/extension angle of the professional group was significantly larger than that of the amateur group (P<0.01). During actions with back steps, the ankle flexion/extension angle of the professional group was significantly larger than that of the amateur group (P<0.01). During actions with steps sideways, hip flexion/extension angle and rotation angle significantly larger than that of the amateur group (P<0.01). During stepping forward, backward and sideways, the loading of the professional group’s joints at the hip, knee, and ankle was always higher in the vertical direction (P<0.01). Furthermore, during Warding off with steps forward (WOF), Laying with steps forward (LF) and Rolling back with steps backward (RBB), hip joint loading increased in the med–lat direction. During actions with steps backward and sideways, the ankle flexion/extension torque and hip abduction/rotation torque of the professional group were significantly larger than those of the amateur group (P<0.01). Different actions in Bafa Wubu activate muscles to different degrees, whereas the iliacus is mainly responsible for stabilizing postures when practitioners perform standing knee lifting motions. Comparing femur loading during walking to the seven sets of motions in Bafa Wubu, when performing Bafa Wubu, participants’ femur loading increases while threshold loading and maximum loading point vary with the actions. Therefore, continuously practicing the seven sets of motions can stimulate the femur in a comprehensive way.Conclusions: Bafa Wubu of Taichi is composed of core techniques of Tai Chi Chuan, characterized by movements in five directions. When performing Bafa Wubu, performers display increased joint angle and joint load at hip, knees, and ankles, consequently enhancing their joint proprioception. Besides, different motions activate muscles of different types at different levels. Also, the threshold of femur load and maximum loading point always change when seven sets of motions in Bafa Wubu are completed coherently. Therefore, it can be concluded that muscles, joints, and bones of the lower extremity can obtain comprehensive and balanced exercise through Bafa Wubu.