Variable Handle-Resistance Based Joystick for Post-stroke Neurorehabilitation Training of Hand and Wrist in Upper Extremities

The objective was to modulate the resistance of a hand-held device, e.g., joystick, for customizing a rehabilitative therapeutic patient-centric virtual environment protocol. Two similar sets of springs (each set having three springs with graded rigidness) were customized to increase the handle-resistance. The springs were experimentally calibrated to determine individual spring-constant value. The amount of exerted force values during joystick movements were standardized in a cohort of healthy subjects (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 15). Coefficient of variation (CV) was calculated to determine the variability among healthy subjects. Further, five (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 5) patients with stroke were enrolled in this pilot study and performed three separate virtual reality sessions using different springs. Task-performance metrics, i.e., time to complete, trajectory smoothness, and relative error, were evaluated for each of the levels. The values of spring-constants as determined experimentally were found to be 1.34 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ± 16.1, 2.23 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ± 29.8, and 6.47 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ± 470.9 N/m for springs with increased rigidity, respectively. The mean force values for different joystick movements were observed to be increasing linearly with increasing spring-rigidity. The calculated CV ≤ 14% indicated the variability in the recorded force values of healthy subjects. Increased task-performance metrics and visual analog scale-fatigue scores for session 2 and 3 as compared to session1, indicated increasing task difficulty at session 2 and 3.