The coordination of reaching and grasping in spastic hemiparesis

The kinematics and intrinsic dynamics of reaching and grasping movements in six subjects with spastic hemiparesis were studied. Movements were perform ed with both hands together as well as with each hand in isolation, and two target widths were used. As expected, large manual asymmetries existed in unimanual task performance. These asymmetries were more pronounced for gras ping than for reaching, which was a consequence of the fact that in graspin g the impaired hand stayed longer at zero velocity before lifting the objec t. This implies difficulties coordinating the more distal movement componen t (hand and fingers). In addition, the impaired hand attained the movement goal with (1) decreased angular range of motion of the joints and (2) an in creased trunk involvement. With respect to the intrinsic dynamics, intra- a nd inter-limb coupling was studied by evaluating cross-correlations of posi tion-time functions joint pairs. In effector space the displacement of the wrist and ipsilateral shoulder were correlated, and in joint-angle space th e elbow extension-shoulder flexion angle pair and the elbow extension-shoul der elevation angle pair were analysed. It was found that despite tight cou plings between the different pairs, the couping strengths for the impaired limb were consistently lower. This was caused by fragmentation of the movem ent, mainly due to a large shoulder involvement at the start of the movemen t concurrent with little or no elbow extension. It is concluded that fragme ntation of the movement, operationalised by the value of the cross-correlat ion between joint pairs is an essential variable by which the level of reco very of function can be captured. It was further shown that the unimpaired hand 'mimicked' the impaired hand on a number of movement characteristics u nder bimanual responding The impaired hand did not change its style of move ment organisation among uni- and bimanual movement responding. It is argued that the apparent stability of the impaired hand can only be sustained at the cost of a decreased flexibility. Finally, inter-limb coupling. assessed by means of cross-correlations of the tangential velocity profiles of both hands, was shown to be high during the course of movement. (C) 2000 Elsevi er Science B.V. All rights reserved. PsycINFO classification: 2300; 2330; 3 250; 3380.