Simulation and experimental analyses of human movement : application to post-stroke hemiparetic gait

Stroke is the leading cause of long term disability with improved walking being an important goal following stroke. Understanding deficits that result in reduced walking performance by hemiparetic subjects is important for the design of effective rehabilitation strategies. The goal of this research was to investigate muscle coordination and mechanical work in hemiparetic walking and mechanisms of acceleration and deceleration in nondisabled walking as a framework for investigating non-steady state walking in hemiparetic subjects. Musculoskeletal modeling and simulation analyses were used to compare individual muscle contributions to important walking subtasks and muscle mechanical work by representative hemiparetic subjects (limited community and community walkers) during pre-swing with a representative speed and age-matched control. Simulation analyses identified decreased paretic soleus and gastrocnemius contributions to forward propulsion and power generation as the primary impairment in the limited community walker compared to the control. Comparison of mechanical work showed that total paretic and non-paretic fiber work was increased in the limited community walker, which was primarily related to decreased fiber and tendon work by paretic soleus and gastrocnemius. The decreased output by the ankle plantar flexors required compensatory work by other muscles. Also, the experimental analyses of accelerated and decelerated walking showed that the ankle plantar flexor moment was positively related to braking and propulsive impulses, which increased with speed. Thus, deficits of the paretic plantar flexors limit forward propulsion and increase mechanical work during pre-swing, and would limit the ability of hemiparetic walkers to accelerate and decelerate, which are essential tasks in daily living activities. For the community walker, simulation analyses showed that deficits in paretic swing initiation are a primary impairment. Specifically, the paretic gastrocnemius and hip flexors contributed less to swing initiation in the community walker compared to the control subject. Total paretic and non-paretic fiber work was increased in the community walker, primarily due to increased work by the hip abductors and adductors. Because step length and step frequency were positively related to walking speed in accelerated and decelerated walking, impaired paretic swing initiation would likely limit the community walker’s ability to accelerate and decelerate.