Abstract
Exoskeleton devices for upper limb neurorehabilitation are one of the most exploited solutions for the recovery of lost motor functions. By providing weight support, passively compensated exoskeletons allow patients to experience upper limb training. Transparency is a desirable feature of exoskeletons that describes how the device alters free movements or interferes with spontaneous muscle patterns. A pilot study on healthy subjects was conducted to evaluate the feasibility of assessing transparency in the framework of muscle synergies. For such purpose, the LIGHTarm exoskeleton prototype was used. LIGHTarm provides gravity support to the upper limb during the execution of movements in the tridimensional workspace. Surface electromyography was acquired during the execution of three daily life movements (reaching, hand-to-mouth, and hand-to-nape) in three different conditions: free movement, exoskeleton-assisted (without gravity compensation), and exoskeleton-assisted (with gravity compensation) on healthy people. Preliminary results suggest that the muscle synergy framework may provide valuable assessment of user transparency and weight support features of devices aimed at rehabilitation.
Highlights
About 15 millions of people experience a stroke every year worldwide [1], and up to 85% of the survivors suffer from limitations in the activities of daily living (ADLs) because of upper limb motor impairment [2,3,4]
The muscle synergy framework was developed to analyze the hypothesis that the central nervous system (CNS) organizes modularly to simplify the production of motor outputs
(2) Weight support features, investigating if LIGHTarm is effectively reducing the magnitude of the temporal components related to spatial synergies
Summary
About 15 millions of people experience a stroke every year worldwide [1], and up to 85% of the survivors suffer from limitations in the activities of daily living (ADLs) because of upper limb motor impairment [2,3,4]. When a high muscle activation is required for completing a task, patients may show abnormal muscle patterns, such as the flexion synergy, with remarkable effects on the kinematic of the movement [18] Besides gravity support, another desired feature for exoskeletons is transparency, or backdrivability. The muscle synergy framework was developed to analyze the hypothesis that the central nervous system (CNS) organizes modularly to simplify the production of motor outputs In such a view, muscle synergies represent a small subset of stored activation patterns on which the CNS can rely on to execute a large number of different movements [27]. A method for the quantitative evaluation based on muscle synergies was carried out to explore the possibility of evaluating user transparency, that is, if the interaction with a passive exoskeleton (the LIGHTarm device) alters muscle synergies spatial and temporal composition, and at what extent, in respect to free movements
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