Robot-assisted reaching exercise promotes arm movement recovery in chronic hemiparetic stroke: a randomized controlled pilot study

Abstract

Background and purpose: Providing active assistance to complete desired arm movements is a common technique in upper extremity rehabilitation after stroke. Such active assistance may improve recovery by affecting somatosensory input, motor planning, spasticity or soft tissue properties, but it is labor intensive and has not been validated in controlled trials. The purpose of this study was to investigate the effects of robotically administered active-assistive exercise and compare those with free reaching voluntary exercise in improving arm movement ability after chronic stroke.

Methods: Nineteen individuals at least one year post-stroke were randomized into one of two groups. One group performed 24 sessions of active-assistive reaching exercise with a simple robotic device, while a second group performed a task-matched amount of unassisted reaching. The main outcome measures were range and speed of supported arm movement, range, straightness and smoothness of unsupported reaching, and the Rancho Los Amigos Functional Test of Upper Extremity Function.

Results and discussion: There were significant improvements with training for range of motion and velocity of supported reaching, straightness of unsupported reaching, and functional movement ability. These improvements were not significantly different between the two training groups. The group that performed unassisted reaching exercise improved the smoothness of their reaching movements more than the robot-assisted group.

Conclusion: Improvements with both forms of exercise confirmed that repeated, task-related voluntary activation of the damaged motor system is a key stimulus to motor recovery following chronic stroke. Robotically assisting in reaching successfully improved arm movement ability, although it did not provide any detectable, additional value beyond the movement practice that occurred concurrently with it. The inability to detect any additional value of robot-assisted reaching may have been due to this pilot study's limited sample size, the specific diagnoses of the participants, or the inclusion of only individuals with chronic stroke.

Figure 1

Description of experimental setup. (a) Photograph of the Assisted Rehabilitation and Measurement (ARM) Guide. A motor (M) actuates a hand piece and forearm trough (T) attached to a user's arm (A) back and forth along a linear track. A six-axis force sensor (F) measures the interaction forces between the user and the device. The ARM Guide can be oriented on a vertical elevation axis (E) and horizontally on a yaw axis (Y). (b) Example of an unassisted (solid line) and motor-assisted (dashed-line) reach by a hemiparetic subject along the ARM Guide. (c,d) Horizontal and vertical arrangements of the targets used for free reaching assessment, free reaching therapy, and robot-based therapy.

Figure 2

Changes in supported fraction of range and fraction of speed. Values are shown for the three preliminary evaluations (weeks 1, 2, and 3), three post-therapy evaluations (weeks 12, 13, and 14), and at the 6-month follow-up evaluation. Plots A and B (left column) show the improved FR_S and FS_S after the training period and sustained values at follow-up for participants in both free reaching and active-assist protocols. Plots C and D show the same results for subjects classified by impairment level. Error bars represent standard deviation across subjects. It should be noted that the statistics are designed to detect within-subject differences, while the figures show between-subject means and standard deviations for illustration of mean values.

Figure 3

Mean changes in FR_S and FS_S by training session. The lower array of plots, each representing a single subject, is included to demonstrate that the mean plots are representative of consistent, steady improvements throughout the course of therapy in individual subjects.