Fellowship for C. Nelson in Support of the effect of chronic hemiparetic stroke on adaptation of the musculoskeletal system and its impact on function

Stroke is the leading cause of long-term disability in the United States, with approximately 795,000 new or recurrent strokes each year. Individuals often have impairments including weakness, spasticity, contractures, and altered muscle activation, which can cause abnormal use of the affected extremity. Over time, these impairments can lead to morphological changes in the architecture of muscle, affecting function. Previous research has already demonstrated that muscle and connective tissue can change after a neurological injury, immobilization, or disuse. However, despite evidence that neural control of the paretic arm is impaired after stroke, how this affects the musculoskeletal system, and how much these deficits contribute to impairments in functional use of the arm is not yet evident. The present proposal will present a novel way to quantify musculoskeletal adaptation after a chronic hemiparetic stroke, and will utilize a musculoskeletal model to investigate how this adaptation alone affects functional use of the paretic arm. I will measure elbow joint stiffness in both arms of individuals with chronic stroke, and will compare this stiffness between the paretic and non-paretic upper extremity. In addition, I will use extended field-of-view ultrasound imaging to quantify muscle fascicle measurements in 3 primary muscles surrounding the elbow joint. I hypothesize that due to motor impairments after stroke, including abnormal synergies and decreased use of the arm, elbow joint stiffness will be increased in the paretic arm. In addition, I hypothesize that paretic muscle fascicle lengths will be shorter for the elbow flexors, and longer for the elbow extensors, as a result of muscle adaptation to the flexed posture seen after hemiparetic stroke. Finally, a musculoskeletal model will be utilized to evaluate the effects of this adaptation on the resting posture and functional reaching movements of the paretic upper extremity. It is hypothesized that even with the ability to control the limb normally, the increased stiffness and shorter muscle fascicles in the elbow flexors would limit the ability to complete functional reaching movements. The overall goal of this proposal is to quantify muscle adaptation after stroke to gain a better understanding of how the musculoskeletal system adapts to the abnormal control seen after stroke. This knowledge will be beneficial to aid in the modification and design of rehabilitation interventions after stroke