Changes in interlimb coordination induced by within-stride changes in treadmill speed.

Human walking involves tightly coordinated movements of the right and left legs. We recently developed and tested a "dynamic treadmill walking" paradigm that changes the treadmill speed within a single step to provide asymmetric training for persons with gait dysfunction. We previously demonstrated that this approach could induce changes in human gait symmetry; however, if this approach is to be used in rehabilitation, we also need to understand how movements of the legs are coordinated to produce these asymmetric gait changes. The goal of this study was to examine the temporal (phase shift) and spatial (center of oscillation difference) aspects of interlimb coordination during dynamic treadmill walking in ten young adults without gait impairment. We found that dynamic treadmill walking drove significant changes in phase shift and center of oscillation difference that were dependent on the timing of the treadmill speed change within the gait cycle. For example, slowing the treadmill during the stance phase extended the double limb support period, and these changes were strongly correlated with a phase shift between the two legs. Accelerating the treadmill late in stance led to extensions in the trailing limb angle that were strongly correlated with changes in the center of oscillation difference. Overall, dynamic treadmill walking can be configured to drive changes in many spatiotemporal, kinematic, and interlimb coordination parameters, creating a variety of options for restoring gait symmetry and targeting aspects of spatial and temporal interlimb coordination in clinical populations with heterogenous patterns of gait asymmetry.