![]() ![]() This coordination is likely impacted by stroke. Separate neural pathways have been suggested for control of the arm and hand ( Galletti et al., 2003 Fattori et al., 2010 Alstermark and Isa, 2012) and the extent of communication between these pathways has been debated ( Wing et al., 1996). ![]() Object manipulation, a common component of task performance, requires further interjoint coordination as the arm must position, orient, and stabilize the hand while the fingers interact with the external object. Increased neural couplings between the distal and proximal muscles could affect the underlying modular structures of the spinal cord that control the arm and hand muscles during functional activities ( Cheung et al., 2012). Indeed, the number of distinct activation patterns available to stroke survivors seems to be reduced ( Roh et al., 2012). These synergies have been shown to extend to finger flexor muscles as well ( Miller and Dewald, 2012 McPherson and Dewald, 2019). Abnormal neurological coupling, as part of a flexion synergy, has also been described between muscles of the elbow and shoulder following stroke ( Dewald et al., 1995 Ellis et al., 2009, 2017). Past studies examining the arm have revealed altered interjoint kinematics in the paretic arm of stroke survivors ( Cirstea et al., 2003) and reduced capacity to create the required joint interaction torques ( Beer et al., 2000). While difficulties occurring at the joint or muscle level, such as hypertonicity ( Katz and Rymer, 1989), spasticity ( Opheim et al., 2014), or weakness ( Ada et al., 2003 Kamper et al., 2006) certainly contribute to functional deficits, impairment of the coordination activity of multiple joints may have an even more profound effect ( Ada et al., 2006). Unfortunately, this dexterity is often compromised by stroke, potentially affecting self-care, employment opportunities, and societal interactions ( Cerniauskaite et al., 2012). The human upper extremity is capable of performing a myriad of functional tasks due to its biomechanical structure and its abundant motor and sensory neural innervation. Increased cocontraction of the hand muscles due to increased neural couplings between the distal and proximal muscles appears to be the underlying mechanism. Our results showed significant proximal-to-distal interactions between finger extension and elbow extension/shoulder abduction of stroke survivors exist during their functional movements. ![]() Proximal kinematics of stroke survivors was also affected by the finger extension, but the cocontraction of their proximal muscles did not significantly increase, suggesting the changes in the proximal kinematics were made voluntarily. Cocontraction of the extrinsic hand muscles of stroke survivors significantly increased at these locations, where an increase in the intermuscular coherence between distal and proximal muscles was observed. Distal kinematics of stroke survivors, particularly hand opening, were significantly affected by the proximal kinematics, as the hand aperture decreased and the duration of hand opening increased at the locations that requires shoulder abduction and elbow extension. Fourteen subjects, including nine chronic stroke survivors and five neurologically-intact subjects participated in an experiment involving transport and release of cylindrical objects between locations requiring distinct proximal kinematics. In this pilot study, we elucidated proximal–distal interactions and their functional impact on stroke survivors by quantitatively delineating how hand and arm movements affect each other across different phases of functional task performance, and how these interactions are influenced by stroke. 6Department of Mechanical Engineering, Korean Advanced Institute of Science and Technology, Daejeon, South KoreaÄespite its importance, abnormal interactions between the proximal and distal upper extremity muscles of stroke survivors and their impact on functional task performance has not been well described, due in part to the complexity of upper extremity tasks.5Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, United States.4UNC/NC State Joint Department of Biomedical Engineering, North Carolina State University, Raleigh, NC, United States.3Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, United States.2Center for Applied Biomechanics and Rehabilitation Research, National Rehabilitation Hospital, Washington, DC, United States.1Department of Biomedical Engineering, Catholic University of America, Washington, DC, United States. ![]()
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