Neuromuscular coordination can be described by combinations of a few muscle synergies, defined as fixed patterns of activation across a set of muscles. Deficits in arm function in post-stroke subjects (PS) are characterized by altered movement coordination involving the shoulder and elbow. Robotic rehabilitation of upper limb in PS has shown promising results in improving their arm function, therefore the aim of this work was to investigate changes in muscle synergies, identified by motor modules and their activation profiles, in PS before and after planar robotic rehabilitation, using our VRRS System.