Locomotor adaptation can persistently reorganize stride-to-stride regulation of centre of mass error dynamics

Locomotor learning in novel environments relies on a gradual alteration of motor output to achieve a desired state. Changes in gait outcomes such as step-length asymmetry are typically used to describe this process. Recently, stability-relevant adaptations, quantified by scalar metrics such as the margin of stability, have also attracted interest. Yet humans, in part, regulate walking stability from stride-to-stride. Scalar metrics only provide instantaneous snapshots of stability and fail to capture rules governing fluctuations from one stride to the next. Here, we investigate whether locomotor adaptation changes how movement regulation evolves across strides using a multidimensional, dynamical systems model of centre-of-mass (CoM) based locomotion error. We apply this approach to split-belt locomotor adaptation, where participants walk on a treadmill with a separate belt for each foot. One belt moves faster than the other, driving participants to adapt compensatory gait patterns due to asymmetry. Using our stride-to-stride model, we find that, in addition to reducing CoM error while adapting, multidimensional error regulation dynamics are also adapted. This structural adaptation persists upon re-exposure to split-belt conditions. Our findings show that split-belt locomotor adaptation includes an adaptation of the structure of stride-to-stride CoM movement regulation and that this structure may be rapidly recalled.