Muscle function following post-stroke locomotor training: a simulation analysis of different strategies to improve walking speed
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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.