CoE parameter directional tuning. Modulation of the CoE parameter across the four aimed directions (N, E, S, W) for each recorded muscle are shown respectively for the healthy subjects group (GR I) and for each patient enrolled in the study. CoE coefficients of each muscle were averaged across repeated trials and, in the case of GR I, also across different subjects (CoE_M). The polar diagrams show the distribution of the CoE_M ±1.96 · SE (SE = Standard Error) coefficients connected by periodic cubic spline interpolation curves. The resulting area inside the curves represents the 95% confidence interval of the CoE distribution for each muscle. Dashed black lines are circles of unit radius. Muscles were ordered according to their relevance in motion production in each direction observed for GR I: in particular TR was responsible for motion toward North direction, DM and DP toward East direction, UT and BI toward South direction, and PM and DA toward West direction.