Influence of trajectory and speed profile on muscle organization during robot-aided training

Active and passive movements are primary control paradigms adopted for robot-aided neurorehabilitation. Deepening the effect of different active and passive robot-aided trainings on muscle organization may allow evaluating the impact of such treatments, and consequently improving the effectiveness of robot-assisted rehabilitation. The aim of this work is to study how different passive strategies adopted in robot-assisted motor rehabilitation affect the muscle organization. For this purpose, seven healthy young subjects were asked to execute point-to-point reaching movements in different directions wearing an upper limb exoskeleton. The task required the execution of active movements at comfortable speed and passive movements accounting for different trajectories and speed profiles. The electrical activity of fifteen upper limb muscles was recorded, and the effect of the choice of the assistive strategy was studied on the level of muscle activation and on the organization of muscle synergies. Our results showed that the passive execution of linear trajectories according to a minimum jerk speed profile promotes a muscle organization more similar to the one elicited during the execution of active movements than in the other passive conditions considered in the analysis. The preliminary results of this study suggest that the choice of the trajectory and speed should be carefully considered in the design of passive robot-mediated rehabilitative trainings.