Joint-Level Responses to Counteract Perturbations Scale with Perturbation Magnitude and Direction

To realize a lower extremity exoskeleton that can provide balance assistance in a natural way, an understanding of human balance control is a necessity. In this study, we investigated how the angle, torque and power of the ankle, knee and hip joints changed in response to balance perturbations during walking. Nine healthy young adults walked on an instrumented treadmill and received pelvis perturbations of various magnitudes and directions at the instance of toe-off right. An open source musculoskeletal modeling package (OpenSim) was used to perform inverse kinematics and inverse dynamics. Subjects modulated the ankle torque in the (left) stance foot with the magnitude and direction of the perturbation. Also in gait phases following foot placement, subjects addressed ankle torques to mitigate the remaining effects of the perturbation. The results presented here support the use of ankle actuation in lower extremity orthoses for natural and cooperative balance control.