Adaptive mediolateral control during split-belt walking: Energetics of interlimb coordination and enhanced savings following acute intermittent hypoxia.

Control of frontal plane mechanics requires active integration of sensory feedback to regulate stability in response to gait perturbations, such as split-belt walking (SBW). In comparison to sagittal plane mechanics, mediolateral (ML) kinematic and kinetic adaptations to split-belt perturbations are less extensively reported. Moreover, the associated metabolic cost of ML adaptations and the retention of previously learned adaptations, defined as motor savings, have not been examined concurrently. We investigated bilateral adaptations in step width and peak ML ground reaction forces to an initial SBW and metabolic cost. We also examined the retention of these adaptations during a subsequent SBW (adapt 2). Given evidence that priming the nervous system with acute intermittent hypoxia (AIH) enhances motor adaptation, we compared the magnitude of these adaptations after AIH. Legs on the fast and slow belt increased step width during initial SBW, but the magnitude of width reduced during adapt 2. Distinct kinetic modulation patterns emerged between legs as the initial increase in ML ground reaction forces was attenuated for the slow leg during the braking impulse phase and for the fast leg during the propulsive impulse phase. Metabolic cost reductions were positively associated with adaptations in ML force but not step width. During adapt 2, individuals who received AIH demonstrated greater reductions in step width and ML ground reaction forces during propulsion, suggesting enhanced motor savings. These asymmetrical ML kinetic adaptations contribute to stability and reduced metabolic cost during SBW. These insights might inform the design of training approaches to improve stability in clinical populations.