Including nonideal behavior in simulations of functional electrical stimulation applications

Simulations of functional electrical stimulation (FES) systems are usually based on the typical or ideal stimulated muscle response, which may result in an overly optimistic prediction of the FES system's performance in real-world applications. We have developed a Simulink block that allows actual nonideal behavior of electrically stimulated muscles to be incorporated into existing FES simulations. This block is based on data collected from complete spinal cord injuries (SCI) subjects, and it modifies the nominal stimulated muscle response to reflect undesirable behavior seen in real-world FES applications, including spasms, tremors, and fatigue. The severity of each type of undesirable behavior can be specified by the user. In this paper, we discuss the design of the block and also present an example of how the block can be used to more accurately assess the probable real-world performance of FES systems prior to testing with SCI subjects.