Quantitative analysis of static sitting posture in chronic stroke

Unsupported sitting requires postural stability of the trunk which is also necessary for almost all activities in daily living, yet there is a lack of research dealing with the persistence of trunk impairment post-stroke using quantitative methodologies. Therefore, the purpose of this study was to investigate unsupported sitting in individuals with chronic stroke by analyzing center of pressure (COP) signals from a force platform. Ten healthy control subjects and ten chronic stroke subjects sat on a chair without a footrest that was placed on top of a force platform. Trials consisted of eyes closed, staring at a target, and COP feedback. COP signals were analyzed using spatial and temporal techniques. Compared to controls, stroke group had larger sway area and larger displacements in all conditions (p<0.05) and less sample entropy (p<0.05) in eyes closed and target conditions. In feedback conditions, both groups had decreased sway area and maximum displacements along with stroke group having increased sample entropy (p<0.05). Our data suggest that trunk control, necessary for unsupported sitting, is impaired well into the chronic stage of stroke onset. Further investigations of sitting should be conducted for better understanding balance deficits under conditions localized to the trunk musculature.