Motor Learning And Savings Of Adaptive Mediolateral Control During Split-Belt Walking

Active control of frontal plane mechanics regulates balance in destabilizing environments, such as during asymmetric split-belt walking. Compared to sagittal plane mechanics, mediolateral (ML) kinematic and kinetic adaptations to split-belt perturbations are not as extensively reported. Moreover, the associated metabolic cost of these adaptations as well as the retention of previously learned ML adaptations upon re-exposure to the same perturbation have not been concurrently examined. We investigated adaptations in step width and peak ML ground reaction forces (GRF) during an initial and subsequent perturbation in order to characterize motor learning and motor savings, respectively. Additionally, we examined the extent to which a neuroplasticity inducing stimulus, acute intermittent hypoxia (AIH), affected the magnitude of each adaptation. Although we observed bilateral increases in step width during the initial adaptation, only the slow leg significantly reduced step width during the subsequent perturbation. Distinct interlimb differences emerged as only the slow leg modulated ML GRF during the braking phase whereas the fast leg increased ML GRF during the propulsive phase. The AIH group uniquely demonstrated greater motor savings of reduced step width and peak ML GRF strategies during the propulsive phase, suggesting greater retention of prior strategies. Furthermore, we find significant associations between ML kinetic adaptations and reductions in metabolic cost. Together, our findings suggest that unlike the sagittal plane, asymmetrical frontal plane adaptations contribute to ML stability as well as reductions in metabolic cost during split-belt walking. These insights could inform clinical training approaches to improve balance and prevent falls in clinical populations.