Browsing by Author "Ramsay, John W."
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Item Muscle morphological changes, compensatory strategies and the use of predictive simulations to direct the rehabilitation of individuals post-stroke(University of Delaware, 2014) Ramsay, John W.In the United States, approximately 795,000 adults are affected by a stroke per year and stroke is the leading cause of adult long term disability. Individuals who have suffered a stroke are often limited in performing many daily functional tasks, especially walking. Therefore, the primary goal of individuals during post-stroke rehabilitation is to regain their ability to walk. Following stroke, muscle weakness contralateral to the brain lesion, or hemiparesis, is the most common impairment. However, it is unclear whether post-stroke muscle weakness is solely due to neurological impairment following stroke, or whether changes in muscle architecture are additional contributing factors. In Aim 1, changes in muscle morphology (i.e. muscle volume, fascicle length and pennation angle) for individual post-stroke dorsiflexor and plantar flexor muscles were quantified using magnetic resonance imaging and ultrasound. The findings indicate that 1) dorsiflexor weakness is not due to changes in muscle architecture and is most likely due to neurological impairments and 2) while individual plantar flexor muscles are affected differently post-stroke, the relative contribution to plantar flexor torque remains the same. Slow walking speed is common for many stroke survivors, and overall function and quality of life improves as walking speed is able to be increased. Therefore, understanding potential factors that may limit speed progression and determining what compensatory mechanisms are utilized to achieve faster walking speeds is important for developing speed-related rehabilitation techniques. In Aim 2, a novel multi-joint hybrid method that utilizes the strengths of both EMG-driven and computed muscle control methods to estimate muscle activations and forces has been developed. Using this method, we found that faster ambulators tended to use a wider range of available hip muscle functions (e.g. abduction and adduction), which was manifested in a circumduction strategy that was mostly regulated by the hip flexors and gluteals. Recent developments in musculoskeletal modeling and computer simulation techniques have enabled the estimation of muscle forces during dynamic tasks and provide insight into the underlying mechanisms of different movement strategies. However, these techniques have been primarily used to describe what does occur rather than predicting what could occur as a result of rehabilitation. In Aim 3, forward dynamic simulations were used to predict the sagittal kinematics during dorsiflexor and plantar flexor functional electrical stimulation (FES) during post-stroke gait. These simulations confirmed that our models have the potential to investigate therapeutic interventions, and also provided the much needed foundation for future research using simulations to predict novel rehabilitation interventions.Item Post-stroke muscle atrophy and intramuscular fat content in hemiparetic subjects(University of Delaware, 2010) Ramsay, John W.Stroke is a leading cause of long term disability in adults, affecting approximately 795,000 adults a year in the United States alone. Following stroke, muscle weakness contralateral to the brain lesion, or hemiparesis, is the most common impairment. Post-stroke hemiparesis is a concern clinically because it restricts many daily living tasks including reaching and grasping, stair-climbing, and most importantly, walking. Among many factors involved in post-stroke hemiparesis is muscle atrophy – a loss of muscle tissue resulting from immobilization, disuse, inactivation, or a combination thereof. Since muscle force is a function of muscle size, the amount of atrophy a post-stroke muscle undergoes is important in adequately describing any changes to its force-generating capability as a result of stroke. Few studies have measured muscle atrophy in post-stroke individuals, and none have attempted to quantify muscle atrophy for individual paretic and non-paretic muscle. In this thesis, Magnetic Resonance Imaging (MRI) and digital reconstruction software were used to measure muscle volumes for individual muscles as well as specific muscle groups in the hemiparetic lower extremity. All muscle volumes were adjusted to exclude non-contractile tissue content, and muscle atrophy was quantified by comparing the volumes between paretic and non-paretic sides. The results of this study suggest that all individual paretic muscles atrophy in relation to the non-paretic side except the gracilis muscle. Besides the gracilis, an average decrease in muscle volume of 23% was observed for the paretic muscles. The gracilis was larger, with an increase of approximately 11%. The gracilis acts not only as a knee flexor, but also as a hip flexor and hip adductor and may increase in volume as ipsilateral hip flexors have been shown to compensate for plantar flexor weakness. The results also suggest that the gastrocnemius atrophies preferentially in the plantar flexor group. Results observed for the muscle groups suggest that the plantar flexor group atrophies preferentially over the dorsiflexors, and that paretic and non-paretic knee flexors and extensors atrophy approximately the same amount. This thesis successfully quantified individual muscle and muscle group atrophy between paretic and non-paretic sides of post-stroke lower extremities. The findings can be used in future studies to develop stroke-specific musculoskeletal models that address additional changes to movement strategies following stroke.