EMG signals, cumulative variance and number of retained muscle synergies according to the adopted criteria. (A) EMG signals related to ten upper limb muscles were collected during robot-mediated treatment. Representative EMGs for a healthy and subacute patient (at 0 and 6 weeks) are shown. Only for graphical purpose data were normalized in amplitude for their maximum value. Labels on the vertical axis are: BRAD, brachioradialis; BRAC, brachialis; BIC, biceps brachii; TRI, triceps brachii; DELA, anterior part of deltoid; DELM, medial part of deltoid; DELP, posterior part of deltoid; LAT, latissimus dorsi; TRAP, trapezius superior; PECM, pectoralis major. Labels on the horizontal axis are: N, North; NE, Northeast; E, East; SE, Southeast; S, South; SW, Southwest; W, West; NW, Northwest. (B) Average values of the cumulative variance related to muscle synergies extracted form the original datasets (solid line) and those extracted from shuffled dataset (dot line) as a functions of the number of extracted synergies for healthy subjects and subacute patients. (C) Histograms of the number of muscle synergies to be retained in accordance with the eigenvalue > 1 criterion (left column) and the slope of the cumulative variance-based criterion (right column).