The Redesign of a Recumbent Tricycle Using a Crank Rocker Mechanism to Increase Power Throughput in FES Cycling

Abstract

This paper presents an investigation of a mechanism to improve the power throughput of persons with tetra- or paraplegia pedaling via functional electrical stimulation (FES). FES stimulates muscle contraction with small electrical currents and has proven useful in building muscle in patients while relieving soreness and promoting cardiovascular health. An FES-stimulated cyclist produces power that is an order of magnitude less than an able-bodied cyclist. At these reduced power levels, many difficulties associated with FES cycling become apparent, namely inactive zones. Inactive zones are defined by the leg being in a position where muscle stimulation is unable to produce power to propel the tricycle forward. A possibility for reducing inactive zones and increasing the power throughput of the cyclist is to alter the motion of a cyclist’s legs. Bicycles have recently been marketed that feature pedaling mechanisms that employ alternate leg motions. This work considers using a four-bar and ratchet-and-pawl linkage in the redesign of a performance tricycle piloted by an FES-stimulated rider. Quasi-static and power models have been optimized for this cycling architecture yielding a design that suggests a 79% increase in throughput power for some FES cyclists. Multiple sets of dimensions are compared against design criteria to identify an ideal design.