The consequence of uneven walking transitory modulation strategies: A simulation-based approach

Abstract

Human gait control involves regulating multiple parameters, particularly when navigating uneven terrain. Terrain perturbations can introduce substantial challenges. While the regulation of total step mechanical work across multiple steps has been studied, other observed measures of gait adjustment remain less explored. Using an analytical model, we examined the center of mass (COM) mechanical work and step frequency cost to evaluate the mechanistic implications of transitory step adjustment strategies reported in the literature. Since COM work represents most walking energetics, mechanical analysis shows a specific threshold for which the cost of going atop a perturbation and extending the step length are equal. The same could be observed when the total cost (work and frequency) is examined. Thus, beyond the point of equilibrium, the strategy with less metabolic cost must be favorable. As this evaluation is based on a Just-in-Time walking strategy, extended lookahead horizon on less complicated terrains may change the preference. Our simulations reveal that transient step length reduction with nominal push-off has less collisional dissipation and, as such, elevated walking momentum post step transition. This strategy can compensate for lost momentum atop terrain perturbations yet, it is costlier than push-off regulation. Hence, it might instead be for foothold selection. An extended step may also be utilized when momentum reduction is needed. Additionally, simulations showed that effective leg length adjustment can not only alter the step length but may also limit COM elevation changes. It in turn limits the work against gravity or perhaps limb loading due to elevated collisions. Therefore, step length adjustments, achieved either by adopting different gait strategies or by controlling the effective leg length, are noted as possible complementary approaches to modulating the magnitude of the push-off and preparation to vault atop a perturbation. We also evaluated the anticipatory control traits of older adults, who are more vulnerable to falls on uneven terrain. Older adults demonstrated a transitory speed decrease before encountering perturbation. This might be an indication that older adults require extra time to select a secure foothold. Even without penalty for the lost time of deceleration, to achieve the average speed after a terrain perturbation encounter, we observe materially increased total mechanical work when the walker slows down just before a perturbation. This added cost likely contributes to the higher mechanical work observed in older adults when walking. Elevated mechanical work demand may contribute to fall incidents in older adults when they are not able to perform adequately.