A modeling approach to understanding poor stability in people with vestibular hypofunction.

People with vestibular hypofunction (PwVH) have poor walking stability, characterized by increased trunk sway, increased spatiotemporal variability, and reduced margins of stability. PwVH may have poor walking stability because of the vestibular loss itself or because they adopt cautious gait patterns to compensate for the vestibular loss (e.g., slower walking with wider and shorter steps). This study used a recently developed model of human walking stability to explore the cause of poor walking stability in PwVH. Results showed that incorporating decreased vestibular sensitivity in the model resulted in increased lateral trunk sway and increased spatiotemporal variability. Reduced margins of stability emerged when the model walked slowly. We performed additional analyses to investigate what controller changes could restore stability metrics to gain insight for potential training mechanisms. In a model with decreased vestibular sensitivity, trunk sway was restored by increasing controller gains dependent on vestibular feedback, reminiscent of vestibular adaptation. Spatiotemporal variability was reduced to normal levels in the presence of decreased vestibular sensitivity by increasing controller gains dependent on somatosensory feedback, reminiscent of sensory reweighting. In contrast, taking wider steps increased margins of stability when walking slowly. Overall, these findings demonstrate that poor walking stability in PwVH may be attributed to both decreased vestibular sensitivity as well as adapted gait mechanics. Furthermore, the model supports current clinical practice of vestibular adaptation and sensory reweighting exercises, as well as modifications to increase gait speed and step width to improve different aspects of walking stability in PwVH.