Effect of Robotic Assistance on the Synergistic Organization of Reaching Movements

Wearable robotic devices for rehabilitation have gained particular interest as they can improve the intensity and repeatability of rehabilitative treatments, leading to better rehabilitation outcomes. However, objective characterization of the effects of robotic interventions is still missing. Here we leverage on muscle synergies theory to provide a quantitative assessment of the effects of an upper limb exoskeleton on the organization of reaching movements in healthy individuals. For this, we computed muscle synergies from 20 subjects performing a standardized reaching task. We found that the robotic assistance does not disrupt the physiological structure of reaching movement but modulates it: a higher number of motor modules are necessary to explain the structure of reaching when using the exoskeleton. We derived an objective analysis of the implications of the more complex and fragmented movement strategy, which can potentially inform the design and testing of robotic prototypes, with the ultimate aim of improving technology-supported rehabilitation interventions.