Increased range of motion and decreased muscle activity during maximal reach with gravity compensation in stroke patients

To stimulate restoration of arm function after stroke, active movement is important, which can be facilitated by supporting the weight of the hemiparetic arm, either in conventional treatment or in other approaches such as robot-aided therapy. During arm support, the active range of motion during reach can increase with respect to unsupported movements. The present objective was to investigate the influence of gravity compensation on muscle activity and range of motion during maximal reach. Six stroke patients performed maximal reaching movements, once with and once without gravity compensation. When comparing these two conditions, muscle activity decreased while range of motion increased with gravity compensation. This implies that gravity compensation may facilitate active arm movements, by reducing the required muscle activity to maintain a particular arm orientation. This may be related to a reduction of an abnormal coupling between shoulder abduction and elbow flexion when arm movements are performed with gravity compensation.