Changing tendons is the main feature of fitness qigong Yijinjing. Changing tendons can enhance the ductility and elasticity of tendons, that is, improve the flexibility of the body. In the process of practicing Qigong Yijinjing, it is beneficial to improve the accuracy of movements, prevent muscle strain, improve the physiological function of the human body and achieve the purpose of strengthening the body by purposefully and systematically exercising the "tendons" or flexibility of the body.