I. Introduction
Every year, nearly 800,000 people have a stroke with over 600,000 of them being first time strokes [1]. These injuries can result in mobility impairments, with strokes being the leading cause of long-term disability with effects ranging from gait instability to falls, especially for people 65 and older [1], [2]. While there are many options for rehabilitative therapy, functional electrical stimulation (FES) is a common option, especially for people with extremely limited or non-existent muscular control. FES has been shown to impart a number of beneficial effects ranging from increased strength to endurance [3]. Precise control of FES however, is extremely difficult for specific rehabilitative motion due to dynamic nonlinearities and inherent inefficiencies such as fatigue [3], [4]. These effects can be compensated for by combining FES with motorized actuators in an exoskeleton, creating a hybrid exoskeleton [5], [6].