The use of wearable robots to provide walking assistance has rapidly grown over the past decade, with notable advances made in robot design and control methods toward reducing physical effort while performing an activity. The reduction in walking effort has mainly been achieved by assisting forward progression in the sagittal plane. Human gait, however, is a complex movement that combines motions in three planes, not only the sagittal but also the transverse and frontal planes. In the frontal plane, the hip joint plays a key role in gait, including balance. However, wearable robots targeting this motion have rarely been investigated. In this study, we developed a hip abduction assistance wearable robot by formulating the hypothesis that assistance that mimics the biological hip abduction moment or power could reduce the metabolic cost of walking and affect the dynamic balance. We found that hip abduction assistance with a biological moment second peak mimic profile reduced the metabolic cost of walking by 11.6% compared with the normal walking condition. The assistance also influenced balance-related parameters, including the margin of stability. Hip abduction assistance influenced the center-of-mass movement in the mediolateral direction. When the robot assistance was applied as the center of mass moved toward the opposite leg, the assistance replaced some of the efforts that would have otherwise been provided by the human. This indicates that hip abduction assistance can reduce physical effort during human walking while influencing balance.

Funding Information
*The Industrial Strategic Technology Development Program (no. 20007058), funded by the Ministry of Trade, Industry, & Energy (MOTIE, Korea), MSIT (Ministry of Science, ICT), Korea, under the High-Potential Individuals Global Training Program) (2021-0-01538) supervised by the IITP (Institute for Information & Communications Technology Planning & Evaluation)
*Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (no. 2021R1A4A3030268)
*R&D Program for Forest Science Technology (no. 2021364B10-2123-BD01) provided by the Korea Forest Service (Korea Forestry Promotion Institute)
*Korea Medical Device Development Fund grant funded by the Korea government (the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health & Welfare, the Ministry of Food and Drug Safety) (RS-2022-00140621).