Self-powered robots to reduce motor slacking during upper-extremity rehabilitation: a proof of concept study

Abstract

Background: Robotic rehabilitation is a highly promising approach to recover lost functions after stroke or other neurological disorders. Unfortunately, robotic rehabilitation currently suffers from “motor slacking”, a phenomenon in which the human motor system reduces muscle activation levels and movement excursions, ostensibly to minimize metabolic- and movement-related costs. Consequently, the patient remains passive and is not fully engaged during therapy. To overcome this limitation, we envision a new class of body-powered robots and hypothesize that motor slacking could be reduced if individuals must provide the power to move their impaired limbs via their own body (i.e., through the motion of a healthy limb). Objective: To test whether a body-powered exoskeleton (i.e. robot) could reduce motor slacking during robotic training. Methods: We developed a body-powered robot that mechanically coupled the motions of the user’s elbow joints. We tested this passive robot in two groups of subjects (stroke and able-bodied) during four exercise conditions in which we controlled whether the robotic device was powered by the subject or by the experimenter, and whether the subject’s driven arm was engaged or at rest. Motor slacking was quantified by computing the muscle activation changes of the elbow flexor and extensor muscles using surface electromyography. Results: Subjects had higher levels of muscle activation in their driven arm during self-powered conditions compared to externally-powered conditions. Most notably, subjects unintentionally activated their driven arm even when explicitly told to relax when the device was self-powered. This behavior was persistent throughout the trial and did not wane after the initiation of the trial. Conclusions: Our findings provide novel evidence indicating that motor slacking can be reduced by self-powered robots; thus demonstrating promise for rehabilitation of impaired subjects using this new class of wearable system. The results also serve as a foundation to develop more sophisticated body-powered robots (e.g., with controllable transmissions) for rehabilitation purposes.

A comparison of the effects and usability of two exoskeletal robots with and without robotic actuation for upper extremity rehabilitation among patients with stroke: a single-blinded randomised controlled pilot study

“…On the contrary, the PSV group might experience more achievement, resulting in an improvement of participation, as re ected by the SIS, but not that of impairment and activity, as re ected by the FMA and WMFT. Similar results were found by a previous study that used a self-powered robot, which manipulated the participants' affected arm using their unaffected arm and induced a higher degree of muscle activation in the affected arm than did externally powered robots, indicating the role of active participation [30]. In addition, those active engagements might induce learning and lasting effects, as shown by the lasting effects of smoothness after intervention in the PSV group.…”

“…Notably, the passive rehabilitation robot showed more bene cial effects with respect to the SIS-function and SIS-social participation compared to the active-assistive rehabilitation robot. Active assistance could induce 'motor slacking' of participants, which is a tendency to minimise metabolic and movement-related costs, thereby preventing active participation and simultaneously developing a dependence on the robot [30]. Motor slacking also possibly affects motivation, attention, effort, and active engagement, which are related to motor cortex excitability and motor plasticity [25,31].…”

Comparison of the effects of and usability of active and active-assistive rehabilitation robots for the upper extremity function among patients with stroke: a single-blinded randomized controlled pilot study

“…Similar results were found by a previous study that used a self-powered robot, which manipulated the participants' affected arm using their unaffected arm and induced a higher degree of muscle activation in the affected arm than did externally powered robots, indicating the role of active participation. [22] In addition, those active engagements might induce learning and lasting effects, as shown by the lasting effects of smoothness after intervention in the ACT group.…”

“…Active assistance could induce "motor slacking" of participants, which is a tendency to minimize metabolic and movement-related costs, thereby preventing active participation and simultaneously developing dependence on the robot. [22] Motor slacking also possibly affects motivation, attention, effort, and active engagement, which are related to motor cortex excitability and motor plasticity. [20,23] Robotic assistance of the ACAS group decrease the loads on the participants' motor systems, which impedes the learning of the fundamentals essential for performing the task.…”

Soft-Wearable Device for the Estimation of Shoulder Orientation and Gesture

“…There have been many attempts to identify the movement of the human body in a virtual way by monitoring the behaviour of the extremities for haptic interfaces [7], teleoperation tasks [1] and assistive and rehabilitation devices [4,16]. Robots increase the number of repetitions performed in a rehabilitation session, thus improving patient morale and motivation [24]. In recent years, rehabilitation devices use sEMG as main source of feedback [15] for control [8].…”