People with severe arm impairment have limited technologies available for retraining their arms, and, if they also have difficulty walking, they often cannot effectively use a manual wheelchair because they cannot grasp and push the pushrim. We are using Lever-Actuated Resonance Assistance (LARA) to solve these problems. A LARA-based device can attach to a manual wheelchair and allow it to be used by people with severe arm weakness in a stationary exercise mode, or for self-powered overground ambulation. LARA uses a lever drive and arm support to appropriately position the arm and to reduce the dexterity required to operate the wheelchair. It also uses mechanical resonance implemented with elastic bands to provide assistance for both stationary exercise and overground ambulation. We first review here pilot results in which we used the LARA method to provide arm therapy to individuals with chronic stroke in stationary exercise mode. We then describe a novel motion-based user interface that allows individuals to control a video game with LARA while operating a wheelchair in resonance. Finally, for overground ambulation mode, we show in simulation that the mechanical resonance provided by LARA theoretically allows people with severe arm weakness to propel themselves with reduced effort and obtain speeds previously unattainable.

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250 word max) Aim: Individuals who require manual wheelchairs after stroke are typically taught to ambulate with compensatory propulsion (i.e. using their nonparetic arm and foot), risking disuse of the paretic arm. We investigated whether stroke survivors can instead ambulate in a bimanual, leverdriven wheelchair that requires the paretic arm to contribute half the propulsive input.Methods: Seventeen individuals with chronic stroke and severe hemiparesis (upper extremity Fugl-Meyer scores between 10 and 24) participated across two experiments. In the first experiment participants (n=12) ambulated in straight paths. In the second experiment participants (n=12) also performed turns, using an improved version of the wheelchair that incorporated handbrakes.Twelve unimpaired controls also completed the second experiment. Motion capture and EMG were used to compare biomechanics between groups.Results: Altogether, 15 of 17 participants with stroke could ambulate 30 m in straight paths, and 9 of 12 could turn 1800° entirely under the power of their paretic arm. Participants with stroke exhibited largely healthy biomechanics, with minimal shoulder hiking/leaning or trunk inclination.Their arm muscle EMG patterns were similar to those used by unimpaired participants, excepting delayed elbow extensor activation.Conclusions: Individuals with severe arm impairment in the chronic stage of stroke retain sufficient strength and coordination with their paretic arm to maneuver bimanual, lever-driven wheelchairs. We suggest bimanual, lever driven propulsion should be explored in stroke rehabilitation practice as an alternative to compensatory wheelchair propulsion, as it has the potential to exercise healthy movement synergies, which may in turn help drive use-dependent motor recovery.

Lever-drive wheelchairs lower physical strain but are less maneuverable than push-rim wheelchairs. Here, we study a possible solution in which the user simultaneously actuates clutches mounted between the levers and wheels each stroke via a clutch handle attached to one lever; this solution is of particular interest for user groups with only one functional hand. First, to demonstrate maneuverability, we show how this "yoked clutch" allows an experienced user to maneuver a constrained space. Then, we compared the difficulty of learning a yoked clutch chair to a conventional lever-drive transmission (i.e. a one-way bearing). Twenty-two unimpaired novice adults navigated a figure-eight track during six training sessions over two weeks. Participant mean speed improved roughly 60% for both chairs, with similar exponential improvement time constants (3 days) and final speeds. However, speed improvement mostly took place overnight rather than within the session for hand-clutching, and the physiological cost index was also about 40% higher. These results indicate that while hand-clutching is no more difficult to learn than a lever-drive, it is reliant on overnight improvement. Also, its increased maneuverability comes with decreased efficiency. We discuss how the yoked clutch may be particularly well suited for individuals with stroke during inpatient rehabilitation.

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