Toward minimum effort reaching trajectories formation in robot-based rehabilitation after stroke: an innovative...

In therapy after stroke, intensive and repetitive training is crucial for relearning of motor abilities and functionalities. Besides conventional therapy, rehabilitation robotic systems are used in the treatment, where a minimum jerk model is used widely in the formation of the point-to-point movement trajectory, which is not necessarily the appropriate choice for hemiparetic upper extremity training. This paper examines and analyzes the influence of a selected form of a flexor muscle tightness on trajectory formation and proposes a guidance scheme that yields minimum effort in robot-assisted arm reaching movement. A dynamic upper extremity model with the three clinically most relevant muscles that develop tightness because of spasticity after stroke was used in the optimization study that examined key features of trajectory formation. The results showed that the trajectories and their velocity profiles become significantly different in the presence of muscle tightness. On the basis of dynamic optimization results, we experimentally examined selected trajectories in a selected individual with chronic hemiparesis. The experimental results confirmed the importance of appropriate selection of reaching trajectories' velocity profiles. The results of optimization and experimentation showed the importance of the velocity profile of the robot-based guidance scheme, which has an influence on the necessary invested 'effort' between starting/ending points to overcome muscle tightness. This study showed that muscle tightness exerts a significant influence on trajectory formation as well as on its velocity profile. The proposed innovative guidance scheme might be useful for practical arm reaching robot-supported movement training in the clinical environment. We suggested that for each hemiparetic patient, the initial identification session before training should experimentally determine the 'optimal' parameters for the rehabilitation guidance scheme that would optimally match the particular muscle tightness constraints.