Improving Arm Function Using Wearable Exoskeletons

This study will collect preliminary data evaluating a body-mounted assistive exoskeleton to facilitate the use of arms impaired by stroke to complete everyday tasks. The central hypothesis is that portable exoskeletons will increase reachable area to enhance function and use of the impaired limb. The rationale for this approach builds on well-established literature on the effects of shoulder unloading on increasing arm workspace in stroke.

A convenience sample of 30 subjects with chronic impairment will be recruited to participate. Participants must have sustained a single stroke, be at least 6-months post stroke, and be in stable condition with residual impairment affecting arm function. Patient metadata will include age, race, gender, height, weight, affected side, and time since stroke. Standardized tests of arm function will measure performance scores of chronic-stage stroke-impaired subjects with and without assistance from the exoskeleton. As a consistency check, scores will be evaluated by at least two independent raters on the same day. The central hypothesis will be tested to achieve our objective through the following 3 specific aims:

Aim 1. Demonstrate that gravity support from a portable exoskeleton can increase the reachable workspace following stroke. Gravity support reduces abnormal muscle synergies (i.e., co-activation patterns) during arm reach tasks, but has not been demonstrated in non-sedentary adults with impairment. The approach combining carbon-fiber reinforced 3D-printed plastics, natural rubber-based energy storage, and customized force profile mechanisms allows similar mechanics that have demonstrated success in stationary arm-supports but in a portable package. To test if similar results can be achieved with a new lightweight system, participants will attempt to perform maximal area sweeps in each of three directional planes (sagittal, frontal, transverse) under two experimental conditions (unassisted, assisted by our portable exoskeleton). The reach workspace in each plane will be measured by kinematic data from a 5-camera Optitrack motion capture system with the wrist center taken as the reach endpoint. It is anticipated that use of the portable exoskeleton will produce highly significant improvements in all three planar reach workspace directions in comparison to unassisted movement, similar to what has been demonstrated previously with stationary (i.e., heavy) robotic systems in the transverse plane.

Aim 2. Determine if a portable shoulder exoskeleton can improve hand function following stroke. While shoulder unloading is known to improve reachable work area by reducing co-contraction of biceps, it may or may not sufficiently reduce co-contraction of wrist muscles, leaving the subject able to reach but not grasp objects. A secondary assistive device at the wrist may be needed by some individuals to allow them to open the hand enough to interact with household objects. To evaluate, the impaired participants will perform simultaneous wrist and finger extension while wearing the shoulder exoskeleton and attempt to pick up objects of varying size from the Action Research Arm Test (ARAT), Wolf Motor Function Test (WMFT), and Box and Blocks (BBT) test kits. For those that are unable to grasp objects from ARAT and WMFT test kits, wrist and finger joint angles will be recorded along with the amount of assistance required to extend the fingers and thumb into a functional grasping pose. It is anticipated that notable improvements in assessment test scores will result from portable assistance, and that the finger extension test will stratify the population into two groups: a) those that do not need additional hand assistance, and b) those that need both shoulder and hand assistance (powered or non-powered) in order to interact with the test objects.

Aim 3. Quantify the effects of assistance from a portable shoulder exoskeleton on changes in functional use of the impaired limb in clinical and home settings. Increasing range of motion does not always lead to functional improvements in daily tasks that involve both arm positioning and fine motor control in the hand. This work will assess changes in functional use of daily objects using well-established clinical assessment tests followed by an in-home trial of a custom-fit portable exoskeleton. Participants with impairment will perform standardized clinical assessments in a laboratory setting that have been shown to correlate with functional performance of activities of daily living including WMFT, ARAT, and BBT. Participants will then complete a Motor Activity Log (MAL) based on activity performed in the past week as a baseline, before wearing the exoskeleton at home for a period of 1-2 hours per day for at least 5 days. At the end of the in-home period, participants will complete a System Usability Scale and a second MAL corresponding with the activities performed while wearing the exoskeleton. It is anticipated that subjects will complete more tasks in less time, with less effort, and with higher success rates in both clinic tests and at-home evaluations.

If successful, body-mounted exoskeletons have the potential to allow ubiquitous training and recovery of arm function at home, dramatically extending therapeutic training time of patients with long-term deficits.