Interactions between foot placement, trunk frontal position, weight-bearing and knee moment asymmetry at seat-off during rising from a chair in healthy controls and persons with hemiparesis.

OBJECTIVE To assess the interaction of foot placement, trunk frontal position, weight-bearing and knee moment asymmetry at seat-off when rising from a chair. DESIGN Cross-sectional study. SUBJECTS Seventeen subjects with hemiparesis and 15 healthy controls. METHODS Trunk position, weight-bearing and knee moment asymmetry were quantified by kinetic and kinematic analysis when the subjects rose from a chair using 3 different foot placements: spontaneous, symmetrical and asymmetrical. Asymmetry was defined by the ratio between sides. RESULTS In the healthy controls, the spontaneous and symmetrical foot placements were associated with an almost vertical trunk position and a symmetrical weight-bearing and knee moment. The asymmetrical foot placement resulted in a trunk displacement towards the foot placed behind, with more weight-bearing and higher moment on this side. The opposite was observed in the hemiparetic participants where the spontaneous and symmetrical foot conditions determined a trunk position and an asymmetry bias towards the unaffected side. Placing the affected foot behind the other reduced the asymmetrical behaviour. CONCLUSION Changes in weight-bearing are partly associated with the frontal trunk position, and foot placement manipulations can be used to modify weight-bearing distribution. Inference on weight-bearing is possible by observing the trunk position during the sit-to-stand task in persons with hemiparesis.