The quantification of rehabilitation progress in post-stroke subjects is essential for establishing the efficacy of a therapy. To achieve that, recent studies have suggested the implementation of the muscle synergy hypothesis, which states that the central nervous system (CNS) reduces the complexity of motor control by activating coordinated groups of muscles, referred to as synergies. Researchers also suggested employing manifold similarity measurements to better evaluate the muscle synergy similarities between the affected subjects and a control group. To validate these hypotheses, this study involved 6 able-bodied subjects (control group) and 13 post-stroke subjects, 6 of whom underwent a Functional Electrical Stimulation (FES) combined with conventional rehabilitation, while the other 7 were subjected to conventional rehabilitation alone.