Browsing by Author "Allen, Jessica Lynn"
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Item Muscle function following post-stroke locomotor training: a simulation analysis of different strategies to improve walking speed(2009-08) Allen, Jessica Lynn; Neptune, Richard R.; Kautz, Steven A.The assessment of rehabilitation effectiveness in the post-stroke hemiparetic population has primarily focused on walking speed. Walking speed, however, may be improved through a number of mechanisms; increased speed can be achieved through a combination of increased propulsion (propelling the center of mass forward) and swing initiation (resulting in longer and faster steps) in either the paretic or nonparetic leg. Therefore the objective of this study was to use a detailed musculoskeletal model and forward dynamics simulations to identify the individual muscle contributions to forward propulsion and swing initiation following locomotor training in two post-stroke hemiparetic patients who had similar speed increases following training, one utilizing an “ankle strategy” (increases in ankle power generation to accelerate the trunk forward) and one a “hip strategy” (increases in hip flexor generation of the swing leg to accelerate the leg forward) to increase speed. Each subject participated in locomotor therapy training using a body weight supported treadmill modality. Strategy classification was based on inverse dynamics analysis pre- and post-training. The simulation analyses revealed that forward propulsion was achieved primarily through the uniarticular plantarflexors and the contralateral knee extensors in both subjects. The main difference between the two strategies occurred primarily in the hip muscle contributions to swing initiation. The “hip strategy” subject, in addition to using the hip flexors to accelerate the leg forward, had higher contributions from the contralateral non-sagittal plane hip muscles to generate energy to the leg to initiate swing. These results suggest that using either the “ankle strategy” or the “hip strategy” to increase speed post-training results in similar muscle function post-training walking with differences primarily occurring in the hip muscle contributions to swing initiation. Future studies analyzing both pre- and post-training may reveal changes in muscle function that correspond more with the strategy classifications.Item Simulation and experimental analyses to assess walking performance post-stroke using step length asymmetry and module composition(2012-08) Allen, Jessica Lynn; Neptune, Richard R.; Abraham, Lawrence D.; Barr, Ronald E.; Deshpande, Ashish D.; Kautz, Steven A.Understanding the underlying coordination mechanisms that lead to a patient’s poor walking performance is critical in developing effective rehabilitation interventions. However, most common measures of rehabilitation effectiveness do not provide information regarding underlying coordination mechanisms. The overall goal of this research was to analyze the relationship between two potential measures of walking performance (step length asymmetry and module composition) and underlying walking mechanics. Experimental analyses were used to analyze the walking mechanics of hemiparetic subjects grouped by step length asymmetry. All groups had impaired plantarflexor function and the direction of asymmetry provided information regarding the compensatory mechanism used to overcome this plantarflexor impairment. Those subjects who walked with longer paretic than nonparetic steps compensated using increased output from the nonparetic leg, while those with symmetric steps compensated using a bilateral hip strategy. These results suggest that step length asymmetry may provide information regarding underlying coordination mechanisms that can be used to guide rehabilitation efforts. Another way to assess walking performance is to directly analyze deficits in muscle coordination. Recent studies have suggested that complex muscle activity during walking may be generated using a reduced neural control strategy organized around the co-excitation of multiple muscles, or modules, which may provide a useful framework for characterizing coordination deficits. Simulation analyses using modular control were performed to understand how modules contribute to important biomechanical functions of non-impaired walking and how the generation of these functions is altered in groups of post-stroke hemiparetic subjects who commonly merged different sets of non-impaired modules. The non-impaired simulation found that six modules are needed to generate the three-dimensional tasks of walking (support, forward propulsion, mediolateral balance control and leg swing control). When the plantarflexor module was merged with the module controlling the knee extensors and hip abductors, forward propulsion and ipsilateral leg swing were impaired. When the module controlling the hamstrings was merged with the module controlling the knee extensors and hip abductors, forward propulsion, body support and mediolateral balance control were impaired. These results suggest that module analysis may provide useful information regarding the source of walking deficits and can be used to guide rehabilitation efforts.