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Post stroke arm impairment : motor variables and movement control McCrea, Patrick Heath


Upper extremity motor impairment is common following stroke and is due to changes in both the central nervous and the musculoskeletal systems. Multiple aspects of stroke induced motor impairment can interfere with one's ability to complete activities of daily living. Weakness (i.e., reduced ability to generate torque) and hypertonia (i.e., increased resistance to passive stretching) impairment dimensions are of particular interest to clinicians as are subsequent adaptations to the control and planning of arm movement. Thus, the purpose of this thesis was to characterize weakness and hypertonia motor impairments and evaluate the planning and control mechanisms underlying a reaching task. We conducted three parallel experiments using twenty persons with chronic arm impairment due to stroke and ten similarly aged healthy control subjects. The first experiment validated a linear spring-damper model of the passive torque response of the elbow and found that mechanical parameters of stiffness and damping were quantitatively related to clinical impairment measures of hypertonia. In the second experiment we characterized the ability to maximally generate torque about eight different joint actions of the upper extremity. We found magnitude and temporal impairments of torque ^ generation in not only the more affected arm but also the less affected arm of individuals with n stroke. The final experiment examined the muscle activation and joint biomechanics underlying natural hand motion during reaching movements to various targets at fast and self-paced speeds. Shoulder abduction was a prominent feature that was related to a clinical scale of motor impairment. Results suggested that post-stroke movement planning is similar to healthy (i.e., different joint trajectories achieved by time scaling joint paths) but that the repertoire of available movement patterns is neurally constrained.

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