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.