Asymmetrical stepping is a characteristic feature of hemiparetic walking and a result of sensorimotor deficits post-stroke. Asymmetry measures (that is, relative performance of paretic leg) may characterize hemiparetic gait better than overall gait performance measures (such as gait speed) and can provide insights into underlying paretic leg impairments. Therefore, the major purpose of this dissertation was to quantify the asymmetry in steps post-stroke and understand its relationship to hemiparetic walking performance. Overall, four studies were conducted. Persons with chronic hemiparesis and healthy controls walked overground and over a split-belt instrumented treadmill as spatiotemporal, kinematic and kinetic data were collected. Clinical assessments included lower-extremity Fugl-Meyer grading and Dynamic Gait Index assessments.

In study one, step length asymmetry during walking was quantified. Results showed that step length asymmetry related to propulsive force generation during hemiparetic walking. Further, asymmetrical step lengths may not necessarily limit the self-selected walking speed likely due to other compensatory mechanisms. We suggest that step length asymmetry can be utilized as a clinical measure to evaluate asymmetrical stepping post-stroke. In study two, step-by-step variability and its relation to asymmetrical stepping were investigated. Results showed that increased spatiotemporal variability, asymmetry in swing and pre-swing time variability and reduced width variability were related to severe hemiparesis, asymmetrical stepping and poor balance. We suggest that step-by-step variability measures are quantifiable markers of impaired walking performance post-stroke.

In study three, asymmetrical stepping was evaluated in a body reference frame. Results showed that anterior-posterior and medial-lateral foot placements relative to body were asymmetrical and this foot placement asymmetry related to step length asymmetry but not step widths. Wider paretic foot placement relative to pelvis than non-paretic also related to reduced paretic leg weight support and lateral instability, suggesting the clinical utility of medial-lateral foot placement relative to pelvis as an outcome to quantify weight support during hemiparetic walking.

In study four, mechanisms underlying step length generation were evaluated. Contralateral anterior-posterior and hip impulses during swing explained the step length variability in the majority of participants. However, relationship of the predictors to step lengths differed in the asymmetrical sub-groups. This implies that mechanisms of step length generation were different across persons showing differing step length asymmetry patterns. Based on these mechanisms, we have proposed specific impairments and therapeutic strategies targeted towards these impairments underlying asymmetrical stepping.