Assistance magnitude versus metabolic cost reductions for a tethered multiarticular soft exosuit

Abstract

When defining requirements for any wearable robot for walking assistance it is paramount to maximize the user’s net metabolic benefit, while limiting the metabolic penalty of carrying the system’s mass. Thus, the aim of this study was to isolate and characterize the relationship between assistance magnitude and the metabolic cost of walking while also examining changes to the wearer’s underlying gait mechanics. The study was performed with a tethered multiarticular soft exosuit during normal walking where assistance was directly applied at the ankle joint and indirectly at the hip due to a textile architecture. The exosuit controller was designed such that the delivered torque profile at the ankle joint approximated that of the biological torque during normal walking. Seven subjects walked on a treadmill at 1.5 m s-1 in one unpowered and four powered conditions where the peak moment applied at the ankle joint was varied from approximately 10% to 38% of biological ankle moment (equivalent to an applied force of 18.7% to 75.0% of body weight). Results showed that with increasing peak exosuit ankle moment, net metabolic rate continually decreased within the tested range. When maximum assistance was applied, the metabolic rate of walking was reduced by 22.83 ± 3.17% relative to the powered-off condition (mean ± s.e.m.).