Movement strategy and EMG activities of the upper extremity at assisted reaching exercise with a 7 DOF collaborative robot.

Recovering of upper extremity functions is important for stroke patients to perform various tasks in daily life. For better rehabilitation outcomes and accurate measurement, robot assisted exercises have been developed. However, there are limited number of studies related to arm muscles activities corresponding to task complexity. We conducted a preliminary case study on strategy and activities of upper extremity muscles in a healthy volunteer at reaching exercise with haptic feedback by a robot with seven degree-of-freedom when a different target was presented in the virtual environment. Impedance control for Franka Emika Panda robot arm has been developed. The study protocol consisted of 4 sets of 40 reaching trials. The trials had two modes with two different feedback: big target task mode and the small target task mode. In each mode both options, with/without haptic feedback were tested. The preliminary results suggest that different distance to target and target's size is related to the change of activation order and intensity of muscle activities at reaching task. Additionally, the haptic feedback required different activation order and higher intensity regardless of the task difficulty.