Shoulder weakness induces trunk compensation after a stroke

International audience ; Most stroke patients do not use their paretic limb even when they are able to do so, often resulting in secondary loss of function. Healthy people adapt their elbow-shoulder-trunk coordination to minimize the torque at the shoulder. The aim of this study is to evaluate how shoulder weakness after stroke impacts elbow-shoulder-trunk coordination. Patients with stroke (> 1 month) and healthy participants performed a reaching task in 2 conditions: high and low shoulder torque. In each condition, the reaching task was first performed spontaneously and second with minimal trunk movement. Elbow-shoulder-trunk coordination was recorded using motion capture, and muscle activation was recorded using EMG. Firstly, most patients had proximal arm non-use and compulsory trunk compensations. Secondly, all patients had lower antigravity shoulder function, leading to saturation of the anterior and medial deltoids when reaching. Third, an antigravity device 1) allows for a more normal level of muscle activation and 2) leads to a decrease in trunk compensations. The observed compensation is not merely a 'poor coordination', but more likely a 'good adaptation' to the weakness of the shoulder after the stroke. Given the beneficial effect of the antigravity device, future work may evaluate the effect of strength training on reducing compensations.