Dynamic postural control during trunk bending and reaching in healthy adults and stroke patients

Postural stability is often task-demand-dependent and often impaired in stroke patients. The purposes of this study were (1) to compare the difference in the center of pressure measures during forward bending of the trunk and reaching on postural actions between normal subjects and stroke patients and (2) to examine the effects of task demands on the center of pressure measures in both groups.

Thirteen normal subjects and 23 stroke patients performed two trials of forward bending of the trunk and reaching for each of the targets at six locations at floor level while standing on a 0.5-m-long pressure mat. Center of pressure excursion, center of pressure average velocity, and bilateral limb weight-bearing ratios characterized the postural actions. Mixed-design analysis of variance was used.

A significant target location by group interaction effects was found for all variables except the center of pressure average velocity. All variables except center of pressure average velocity showed significant group differences. The center of pressure excursion and bilateral limb weight-bearing ratio were smaller, and the center of pressure average velocity was larger in stroke patients than in normal subjects. The effects of target location on variables measured were prominent in stroke patients. The posturography of stroke patients was less regular than that of normal subjects. Stroke patients tended to avoid shifting their center of pressure toward the affected side, even when highly necessary.

The difference of postural actions between groups depended on task demands. Small center of pressure displacement and fast center of pressure velocity characterized decreased adaptive postural actions. The amount of center of pressure shift and center of pressure velocity were also dependent on the task demands for both groups.