The Effect of Object Position and Object Changes on Postural Adjustment during Seated Reaching Movements

Abstract

The purpose of this study was to investigate the effects of the change of position of an object in relation to the subject and the change of the nature of the object, on the postural adjustments during seated reaching movements in healthy subjects and in hemiplegic patients. The subjects were 12 healthy volunteers who were neurologically intact (healthy group) and 10 hemiplegic patients (patient group). Subjects reached with the right hand to lift and drink water from two types of cups under three different reach conditions: straight forward, 45゜toward the right side, and 45゜across the body toward the left side. The subjects in the patient group reached out with the unaffected hand. The hand reach time, vertical ground reaction force, and EMG activity were analyzed for each of the six conditions. A significant object position effect was found with the vertical ground reaction force variable and the leg muscle activity in the hemiplegic patients. A two-way analysis of variance was conducted. In both groups, the effect of the change of the object on postural adjustment was significant, and the effect of the change of the position of the object on postural adjustment was not significant. However, it is suggested that the change of the position and a change in the nature of the object strongly influence postural adjustment in hemiplegic patients. It was found that the postural adjustments during reach is different for the two groups.