Identification of low torque step sizes for the design of a single-channel muscle-powered hybrid orthosis for people with spinal cord injury

In paraplegia due to complete or incomplete spinal cord injury, the connection from the brain to muscles in the lower limbs is severed but the muscles that act on signals from the brain to produce limb movement remain functional. Functional electrical stimulation (FES), which is the application of electric potential across a muscle group to artificially cause the muscle to contract, is a method that can be used alone or in conjunction with an orthosis to produce a gait cycle. Such FES based walking machines or devices have been studied and designed for several decades. However, their application in everyday exercise is limited by several factors, one of which is the rapid onset of muscle fatigue produced in the stimulated muscle. In this work, simulations were conducted in Simscape Multibody to lay the groundwork for the design of a next-generation FES based walking machine powered by the quadriceps femoris muscle group of each limb. The stimulation of the quadriceps femoris muscle causes the knee to extend while some energy is stored by the orthosis, which uses the stored energy to complete the gait cycle. In this study, we have analyzed the power requirements of each step in the hybrid FES-orthosis gait cycle for different stride lengths. These requirements can help identify small step sizes to reduce the power required from the stimulated muscle.