An artificial reflex improves the perturbation-resistance of normal and spastic walking - A simulation study -

Abstract

Walking assist systems should cope with both the external perturbation caused by slips, uneven terrain, slopes, and obstacles, and local function impairment caused by internal factors, like spastic paralysis. It is known that humans are able to cope with these difficulties by different strategies. One is that in the case when external perturbation occurs, especially when the occurrence cannot be predicted or perceived in advance, humans rely on reflexes, which cause unconscious, relatively fixed muscular response patterns to perturbations within a short period of time. Another is that in the case of local function impairment, humans generally develop compensated gait to overcome the falling-down risky factors. Our goal is to realize these strategies for real-world walking support systems, e.g. robotic systems, for gait-impaired people, whose afferent and efferent neural pathways are usually weakened, so that the walking function including reflexive system is also impaired to a certain degree. In this study, we investigated these strategies by constructing a human walking model that consists of central pattern generator (CPG) module and musculo-skeleton module. We adopted 'slips' that frequently occur in daily living as an external perturbation. As the reflexive mechanism, we used muscle activity profiles acquired from human gait experiments, together with a CPG-phase-modulation, and we examined of the roles of these two reflexive mechanisms. Besides, we modeled spastic gait by modulating several specific neuron's output, in order to study another strategy, compensated walking. We also explored the validity of our reflexive mechanisms against slips in the case of the spastic gait. The results indicated that the simulation model could display behavior resembling that of normal human walking, and on the occurrence of a slip-perturbation, together with the CPG-phase-modulation, the rapid muscular response could improve perturbation-resistance and maintain balance for the simulated normal walker. Moreover, a spastic walker with pes equines and compensatory actions was simulated, and we confirmed that the reflexive mechanisms against slips could also improve the perturbation resistance for the spastic walking.