A simple approach to estimate muscle forces and orthosis actuation in powered assisted walking of spinal cord-injured subjects

Abstract

Simulation of walking in individuals with incomplete spinal cord injuries (SCI) wearing an active orthosis is a challenging problem from both the analytical and the compu-tational points of view, due to the redundant nature of the simultaneous actuation of the two systems. The objective of this work is to quantify the contributions of muscles and active or-thosis to the net joint torques, so as to assist the design of active orthoses for SCI. The func-tional innervated muscles of SCI patients were modeled as Hill-type actuators, while the idle muscles were represented by stiff and dissipative elements. The orthosis was included as a set of external torques added to the ankles, knees and hips to obtain net joint torque patterns sim-ilar to those of normal unassisted walking. The muscle-orthosis redundant actuator problem was solved through a physiological static optimization approach, for which several cost func-tions and various sets of innervated muscles were compared.