Postural sway assessment in hemiparetic patients during body weight distribution changes

Abstract

Introduction: Stroke events is usually accompanied by deficits in the control of postural stability. Among the signs of altered postural control in post-stroke individuals, the asymmetric body weight-distribution (BWD) between the lower limbs is one of the most evident. The visual feedback of the feet center of pressure (CP) is widely used as a therapeutic tool for BWD correction. The pattern of postural sway of post-stroke individuals during visual feedback tasks, however, is not fully elucidated. Understanding this pattern can give us important information about how postural control is affected during these tasks, supporting the development of more efficient interventions. Objective: The purpose of this study was to investigate the postural sway pattern of post-stroke individuals during visual feedback tasks to correct BWD asymmetry. Methods: Thirty individuals affected by stroke were placed on the force platform and instructed to perform two tasks: (i) to remain in the orthostatic position (quiet posture); (ii) to distribute their body weight symmetrically between the lower limbs, making use of the visual feedback of their own CP (feedback task). A single 60s test was performed for each task, with an interval of 1-2 min in-between. The CP coordinates were obtained at 50Hz through a force platform. From the lateral displacements of CP, the following variables were calculated: the percentage of total body mass distributed over the paretic limb (BWD); the standard deviation (SDLAT); the mean velocity (MVLAT) and the mean frequency (MFLAT). The Wilcoxon test was used to compare tasks (quiet posture vs. feedback), assuming α=0.017. Results: Post-stroke individuals could maintain a symmetrical BWD during the feedback task (BWD ~5%) when compared to the quiet posture (BWD ~10%). There were significant differences for SDLAT (P<0.001) and MVLAT (P<0.001), but not for MFLAT (P=0.658), indicating that postural sway displacement during the feedback task was greater and faster than in the quiet posture condition. Conclusion: Post-stroke individuals have a more unstable postural displacement pattern during the maintenance of a symmetrical BWD guided by visual feedback. This behavior indicates that visual feedback is not sufficient to compensate for changes in postural control in these individuals, with rise questions about the use of visual feedback in balance rehabilitation program.