Simple within-stride changes in treadmill speed can drive selective changes in human gait symmetry

Abstract

ABSTRACTBackgroundMillions of people worldwide are affected by clinical conditions that result in gait asymmetry (e.g., stroke, cerebral palsy, lower limb amputation). There is a need for customizable rehabilitation approaches that can flexibly target different aspects of gait asymmetry with minimal need for specialized equipment. Here, we studied how simple within-stride changes in treadmill speed could drive selective, predictable changes in human gait symmetry.MethodsIn Experiment 1, ten healthy young adults walked on an instrumented treadmill with and without a closed-loop controller engaged. The controller changed the treadmill speed to 1.50 m/s or 0.75 m/s depending on whether the right or left leg generated propulsive (i.e., forward-directed) ground reaction forces, respectively. In Experiment 2, a separate group of ten healthy young adults walked on the treadmill with and without an open-loop controller engaged. This controller changed the treadmill speed to 1.50 m/s or 0.75 at a prescribed time interval. We used a metronome to guide the participants to step at a series of different time points relative to the controller-driven speed change. We collected kinematic and kinetic data in Experiments 1 and 2.ResultsIn Experiment 1, participants walked with asymmetric kinematics and ground reaction forces when the closed-loop controller was engaged. The leg that accelerated during propulsion (right leg) showed a smaller leading limb angle and a larger trailing limb angle than the leg that decelerated during propulsion (left leg). The right leg also generated smaller propulsive forces than the left leg. In Experiment 2, the patterns of asymmetry in spatiotemporal gait parameters, kinematics, and ground reaction forces depended on the timing of the speed change within the gait cycle. Step times, leading limb angles, and peak propulsion became asymmetric when the treadmill speed changed early in stance. When the treadmill speed changed later in stance, step lengths, step times, and propulsion impulses became asymmetric.ConclusionsSimple manipulations of treadmill speed can drive predictable, selective changes in human gait symmetry. Future work will explore this customizable technique as a potential approach for restoring gait symmetry in clinical populations.