A study on balance maintenance strategies during 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. In this study, we investigated the both strategies by constructing a human walking model that consists of Central Pattern Generator (CPG) module. 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 a spastic hemiplegic gait by modulating some specific neuron's output, in order to study another strategy, compensated walking. 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 walker. Moreover, the pes equinus caused by the spasticity in Gastrocnemius could be modelled and falling down risk resulted from the pes equinus could be reduced by the simulated compensated walking.