A functional tracking task to assess frontal plane motor control in post stroke gait.

The ability to execute appropriate medio-lateral foot placements during gait is thought to require active frontal plane control and to be critical in maintaining upright posture during gait. The aggregate frontal plane metrics of step width and step width variability have been assessed for post-stroke populations, but only under normal walking conditions. However, in the case of stroke, limb specific differences in sensory-motor control are likely. Thus, an investigation of limb specific motor control characteristics under tracking task conditions is needed to appropriately characterize frontal plane sensory-motor control post-stroke. Chronic stroke subjects (n=15) and age matched control subjects (n=10) tracked static, bilateral foot placement targets at self-selected walking speeds and completed a free walking trial. Variability and error of tracking performance were analyzed for step width and foot placement. Stroke subjects demonstrated reduced ability to control step width variability and foot placement variability, compared to control subjects. Step width variability and affected limb foot placement variability were sensitive to task complexity, increasing significantly in response to a decrease in step width target size. These results show that stroke mediated changes in the sensory-motor integration processes are manifested as inter-limb differences in frontal plane motor variability during a gait tracking task, with an additional sensitivity to task complexity. Additionally, the proposed step width tracking paradigm presents a clinically reproducible motor control metric that can be used for diagnostic assessment or as a potential outcome for a gait training regimen.