Compensatory strategies for reaching in stroke

A major prerequisite for successful rehabilitation therapy after stroke is the understanding of the mechanisms underlying motor deficits common to the se patients. Studies have shown that in stroke patients multijoint pointing movements are characterized by decreased movement speed and increased move ment variability, by increased movement segmentation and by spatial and tem poral incoordination between adjacent arm joints with respect to healthy su bjects. We studied how the damaged nervous system recovers or compensates f or deficits in reaching, and correlated reaching deficits with the level of functional impairment. Nine right-hemiparetic subjects and nine healthy su bjects participated, All subjects were right-hand dominant. Data from the a ffected arm of hemiparetic subjects were compared with those from the arm i n healthy subjects. Seated subjects made 40 pointing movements with the rig ht arm in a single session, Movements were made from an initial target, for which the arm was positioned alongside the trunk. Then the subject lifted the arm and pointed to the final target, located in front of the subject in the contralateral workspace. Kinematic data from the arm and trunk were re corded with a three-dimensional analysis system. Arm movements in stroke su bjects were longer, more segmented, more variable and had larger movement e rrors. Elbow-shoulder coordination was disrupted and the range of active jo int motion was decreased significantly compared with healthy subjects, Some aspects of motor performance (duration, segmentation, accuracy and coordin ation) mere significantly correlated with the level of motor impairment. De spite the fact that stroke subjects encountered all these deficits, even su bjects with the most severe motor impairment were able to transport the end point to the target. All but one subject involved the trunk to accomplish t his motor task. In others words, they recruited new degrees of freedom typi cally not used by healthy subjects. The use of compensatory strategies may be related to the degree of motor impairment: severely to moderately impair ed subjects recruited new degrees of freedom to compensate for motor defici ts while mildly impaired subjects tended to employ healthy movement pattern s. We discuss the possibility that there is a critical level of recovery at which patients switch from a strategy employing new degrees of freedom to one in which motor recovery is produced by improving the management of degr ees of freedom characteristic of healthy performance. Our data also suggest that stroke subjects may be able to exploit effectively the redundancy of the motor system.