Dynamic gait stability and limb support contributing to falls following a novel standing-slip in ambulatory people...

Multiple sclerosis (MS) increases the risk of falls. Understanding how people with MS (PwMS) respond to sudden balance disturbances is critical for developing effective fall prevention strategies. This study exposed PwMS to an unexpected slip during treadmill standing and compared the responses between fallers and non-fallers. Twenty-three participants experienced one unanticipated standing-slip while secured by a safety harness. The primary outcome was dynamic gait stability, as defined by the Feasible Stability Region theory, and limb support quantified by hip height. Secondary measures included recovery step characteristics (length, latency, duration, and speed), slip distance, and trunk angle. Fifteen participants were classified as fallers and eight as non-fallers. Non-fallers showed significantly better stability at liftoff and touchdown (p < 0.001). The non-fallers also exhibited shorter step latencies (p < 0.001), reduced slip distances (p < 0.001), and better limb support at liftoff (p = 0.011) and touchdown (p = 0.012). Fallers displayed a more backward trunk angle at liftoff (p = 0.008), though trunk angle at touchdown did not differ significantly (p = 0.093). The recovery step latency strongly correlates with stability and limb support at liftoff (p < 0.001 for both). This study identifies key biomechanical differences between fallers and non-fallers during slip recovery in PwMS. Non-fallers demonstrated greater stability, quicker step initiation, shorter slip distances, better vertical limb support, and a less backward trunk angle at liftoff than the fallers. These findings underscore the roles of controlling dynamic gait stability and limb support through timely stepping and effective trunk control in fall prevention, thereby enhancing our understanding of fall risk in PwMS.