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. / text

Post-stroke hemiparesis usually leads to slow and asymmetric gait. Improving walking ability, specifically walking speed, is a common goal post-stroke. To develop effective post-stroke rehabilitation interventions, the underlying mechanisms that lead to changes in walking ability need to be fully understood. The overall goal of this research was to investigate the deficits that limit hemiparetic walking ability and understand the influence of post-stroke rehabilitation on walking ability in persons with post-stroke hemiparesis. Forward dynamics walking simulations of hemiparetic subjects (and speed-matched controls) with different levels of functional walking status were developed to investigate the relationships between individual muscle contributions to pre-swing forward propulsion, swing initiation and power generation subtasks and functional walking status. The analyses showed that muscle contributions to the walking subtasks are indeed related to functional walking status in the hemiparetic subjects. Increased contributions from the paretic leg muscles (i.e., plantarflexors and hip flexors) and reduced contributions from the non-paretic leg muscles (i.e., knee and hip extensors) to the walking subtasks were critical in obtaining higher functional walking status. Changes in individual muscle contributions to propulsion during rehabilitation were investigated by developing a large number of subject-specific forward dynamics simulations of hemiparetic subjects (with different levels of pre-training propulsion symmetry) walking pre- and post-locomotor training. Subjects with low paretic leg propulsion pre-training increased contributions to propulsion from both paretic leg (i.e., gastrocnemius) and non-paretic leg muscles (i.e., hamstrings) to improve walking speed during rehabilitation. Subjects with high paretic leg propulsion pre-training improved walking speed by increasing contributions to propulsion from the paretic leg ankle plantarflexors (i.e., soleus and gastrocnemius). This study revealed two primary strategies that hemiparetic subjects use to increase walking speed during rehabilitation. Experimental analyses were used to determine post-training biomechanical predictors of successful post-stroke rehabilitation, defined as performance over a 6-month follow-up period following rehabilitation. The strongest predictor of success was step length symmetry. Other potential predictors of success were identified including increased paretic leg hip flexor output in late paretic leg single-limb stance, increased paretic leg knee extensor output from mid to late paretic leg stance and increased paretic leg propulsion during pre-swing. / text