Savings and interference effects of sequential gait interventions

Sequential application of gait interventions is common in rehabilitation programs, but the interaction between the motor adaptation mechanisms engaged by different interventions is underexplored. For example, split-belt treadmill training (SBT) and asymmetric rhythmic auditory cueing (ARAC) are interventions that can exert similar gait asymmetry in timing; however, they engage different motor adaptation mechanisms with different underlying neural correlates. SBT engages sensorimotor adaptation, driven by the participant’s perception of belt speed, and ARAC actively instructs step timing. This study examined how intervention order and temporal congruence influence gait adaptation and after-effects. Temporal congruence was defined by whether the two interventions prescribed the same or opposing asymmetry patterns. Seventeen healthy adults consented to participate; 11 completed all six treadmill walking conditions, and 10 were included in the final analysis. The conditions comprised two single-intervention controls and four sequential combinations of SBT and ARAC in temporally congruent or incongruent forms. Step length, step time, and peak vertical ground reaction force asymmetries were measured using motion capture and force plates during baseline, adaptation, and post-adaptation stages. Early and late adaptation, as well as early and late post-adaptation, were analyzed with repeated-measures models to assess order, congruence, and stage effects. Order effects were most evident for spatial and kinetic measures. Conditions ending with split-belt treadmill walking produced greater after-effects and retention magnitudes than those ending with ARAC. Temporal congruence influenced adaptation only when SBT preceded ARAC ( p < 0.05) and had no effect on post-adaptation outcomes ( p > 0.05). Significant retention was observed only for step length asymmetry, with the largest values following continuous split-belt exposure (15 min) compared to sequential protocols involving shorter exposure (7.5 min). The sequence of sensorimotor and instructional gait interventions influenced both the magnitude and the extent to which it persisted after removal of the perturbation. Placing SBT later in a training session enhanced after-effects and retention of step length asymmetry more than when it was applied first. This study demonstrates order and temporal congruence effects across two distinct adaptation mechanisms in a sequential gait paradigm, showing that order, rather than congruence, predominantly determines after-effects and retention.