Work with me, not for me: Relationship between robotic assistance and performance in subacute and chronic stroke patients.

Introduction Studies in robotic therapy which applied the performance enhancement approach report improvements in motor performance during training, though these improvements do not always transfer to motor learning. Objectives We postulate that there exists an assistance threshold for which performance saturates. Above this threshold, the robot's input outweighs the patient's input and likely learning is not fostered. This study investigated the relationship between assistance and performance changes in stroke patients to find the assistance threshold for performance saturation. Methods Twelve subacute and chronic stroke patients engaged in five sessions (over two weeks, each 60 min) in which they performed a reaching task with the rehabilitation robot H-Man in presence of varying levels of haptic assistance (50 N/m to 290 N/m, randomized order). In two additional sessions, a therapist manually tuned the assistance to promote maximal motor learning. Results Higher levels of assistance resulted in smoother and faster performance that saturated at assistance levels with K >= 110 N/m. Also, the therapist selected assistance levels of K = 175 N/m or below. Conclusion The findings of the study indicate that low levels of assistance (K <= 175 N/m) can sufficiently induce a significant change in performance.