Fig. 2

Scheme of muscle-to-action mapping-based training of abnormal muscle synergies after stroke. Based on an analysis of existing muscle synergies in the more-affected limb, target changes in muscle synergy vectors (\(\Delta \text{W})\) or activation profiles (\(\Delta \text{C}\)) are configured. These target changes in muscle synergies are utilized in a biomechanical model to estimate target action patterns, such as endpoint force (\(\Delta \text{F})\) or joint rotations (\(\Delta \text{M})\). The resultant actions (\(\text{F}{\prime}\) or \(\text{M}{\prime}\)), obtained by adding the estimated changes in actions to habitual (i.e., pre-training, \(\text{F}\) or \(\text{M}\)) actions, are assigned as training tasks. Following a specific period of training, the modified muscle synergies are evaluated to update the target changes in muscle synergies