Deficits in surface force production during seated reaching in people after stroke

In order to design effective treatment strategies for the rehabilitation of reaching after stroke, it is necessary to understand the underlying deficits. Although the kinematic aspects of reaching after stroke have been studied frequently, little attention has been paid to the surface force production underlying this behavior. The purpose of this study was to investigate surface force production and its coordination with arm movement during seated reaching in a group of people with hemiparesis.

Seven people with mild right hemiparesis after stroke and 7 people who were neurologically healthy participated.

Subjects performed seated reaching at 160% their normal speed toward ipsilateral and contralateral targets placed 160% beyond arm reach. Surface forces beneath the seat and feet and 3-dimensional hand movement and joint motions of the upper extremity and trunk were recorded.

A weight shift from seat to feet occurred earlier whereas the onset of medial-lateral seat force was delayed and smaller in magnitude in people with hemiparesis.

The results suggest that the normal magnitude and timing of surface force production during reaching beyond arm's length are altered in people with even mild hemiparesis after stroke, particularly during reaching toward the hemiparetic side.