Design for Hip Abduction Assistive Device Based on Relationship Between Hip Joint Motion and Torque During Running

Abstract

Numerous attempts have been made to reduce metabolic energy while running with the help of assistive devices. A majority of studies on the assistive devices have focused on the assisting torque in the sagittal plane. In the case of running, however, the abduction torque in the frontal plane at the hip joint is greater than the flexion/extension torque in the sagittal plane. During running, as does an elastic body, the abduction torque and the motion of the hip joint have a linear relationship, but are opposite in direction. It is expected that the hip abduction torque can be assisted with a simple passive method by using an elastic body that reflects the movement characteristics of the hip joint. In this study, therefore, a system to assist hip abduction torque using a leaf spring was proposed with a prototype testing. While running with the assist system proposed, the leaf spring aids the abduction torque on the stance phase, and the torque is not generated due to the passive revolute joint on the swing phase. The joint angle is changed with respective to the rotation in the flexion/extension direction to prevent discomfort torque during swing phase and to increase the duration of the torque action during stance phase. A preliminary test was conducted on one subject using the prototype of the hip joint abduction torque assistive device. The participant with the assistive device reduced metabolic energy by 5% compared to the case without abduction torque assist while running at 2.5m/s. In order to increase the amount of metabolic reduction, the device shall be supplemented by system mass reduction and hip joint position optimization.