Characteristics of unsuccessful reactive responses to lateral loss of balance in people with stroke.

Purpose: The effectiveness of reactive responses to a sudden loss of balance is a critical factor that determines whether a fall will occur. We examined the strategies and kinematics associated with successful and unsuccessful balance recovery following lateral loss of balance in people with stroke (PwS).

Methods: Eleven PwS were included in the analysis. They were exposed to unannounced right and left horizontal surface translations and demonstrated both successful and unsuccessful balance responses at the same perturbation magnitude. Reactive step strategies and kinematics were investigated comparatively in successful and unsuccessful recovery tests.

Results: The crossover strategy was used in most of the unsuccessful tests (7/11) while the unloaded-leg side-step in the successful tests (6/11). There were no significant differences in the reactive step initiation time in unsuccessful vs. successful tests. However, the step execution time, step length and center of mass displacement were significantly higher during the first recovery step in unsuccessful tests.

Conclusions: PwS have difficulties in controlling and decelerating the moving center of mass following a lateral loss of balance. The increased step time and step length of the first reactive step in unsuccessful vs. successful tests suggest the crossover step strategy may be ineffective for PwS.