Alkis Hadjiosif is a Postdoctoral Fellow at Johns Hopkins University. He received his Diploma in Electrical and Computer Engineering from the National Technical University of Athens, Greece in 2008 and his PhD in Bioengineering from Harvard University in 2015 studying the influence of environmental variability in motor adaptation. His research aims to understand mechanisms of motor learning and motor control, in both healthy individuals and ones afflicted by motor disorders, and leverage this understanding to improve the assessment and rehabilitation of neurological impairment in the motor system.
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Abstract
Post-stroke Postural Abnormalities in the Arm and Their Relationship to Loss of Motor Control
Abnormal resting postures are one of the most common and widely recognizable motor symptoms after stroke. For example, the typical hemiparetic arm posture consists of flexion at the fingers, wrist, and elbow. This pattern appears to parallel the abnormal muscle synergies during active movement, such as the abnormal coupling of muscles that move the shoulder vs. the elbow joint. Whether these synergies are generated by the same mechanism as abnormal resting postures remains an open question; it might instead be that resting abnormalities are inactive during movement. Also unknown is the degree to which resting postural abnormalities influence active moving and holding.
Here we systematically assessed resting postural abnormalities in stroke patients. We found that patients exhibited abnormal postural forces at rest, which mirrored characteristics of abnormal synergies: for example, postural abnormalities were markedly lower when the arm was supported against gravity, and, critically, strongly related to the Fugl-Meyer scale, a measure based on abnormal synergies. These findings suggest a shared mechanism between resting abnormalities and abnormal synergies after stroke.
We then examined whether these resting postural abnormalities affected the motor control of active reaching in the same workspace. We did not find any systematic effects of resting postural forces either across patients with different resting posture magnitudes, nor between high- vs. low-resting postural force regions for the same patient. However, we found evidence suggesting that resting postural abnormalities might influence active holding control. We conclude that post-stroke deficits in posture and movement may be driven by separate mechanisms. Moreover, our findings identify arm support as a way to alleviate these resting postural abnormalities.