Providing unloading by exoskeleton improves shoulder flexion performance after stroke

Robotic devices can be engaged actively or passively to unload arm weight or impose additional loading. The conditions of variable loading and unloading offer an opportunity to investigate motor performance of the arm affected by a stroke. The objective of this study was to investigate the interactive effects of the proximal arm impairment and passive weight compensation on shoulder flexion performance in the sagittal plane after stroke. Twenty-eight participants (age 57 ± 10 years, 21/28 ≤ 6 weeks post-stroke) played a shoulder flexion game under five standardized weight compensation configurations provided by the Armeo^®Spring exoskeleton. Percent of targets acquired and root mean square error were calculated to derive three behavioral and three kinematic outcomes: total score/overall error (loading/unloading conditions and five configurations combined), loading and unloading score/error (five configurations combined), and weight compensation configuration score/error for each setting separately. The total score was positively related and the overall error was negatively related to proximal arm impairment (Fugl-Meyer upper extremity movement subscale, maximum 30, FM30). The unloading score (80 ± 27%) and error (5 ± 4°) were significantly better than the loading score (45 ± 38%, p < 0.01) and error (14± 9°, p < 0.01) with improvements most pronounced in the mid-range of FM30 (4-15 points). The configuration scores/error gradually improved with each increment in unloading for the mid-range FM30 participants, while only error improved in those with low FM30. In conclusion, shoulder flexion performance depends on proximal arm impairment, but it is also influenced by the degree of unloading/loading provided, particularly among individuals with moderate paresis after stroke.