Interference and Motor Memory Consolidation Effects of Sequential Gait Interventions: A randomized controlled trial

Background Sensorimotor adaptation and instructional adaptation have been found to be motor learning processes that exhibit additive characteristics when applied simultaneously. This study investigates the effects on acquisition and retention of gait outcomes when interventions corresponding to sensorimotor and instructional learning processes are applied sequentially, i.e., split-belt treadmill training (SBT) and (asymmetric) rhythmic auditory cueing (ARAC), respectively. Factors evaluated include order of sequential intervention, congruence between subsequent interventions, and the relative contribution(s) of each intervention in the acquisition and retention of gait (a)symmetry. Methods The repeated-measures study involved six randomized sessions; two controls included SBT and ARAC individually. Four sessions included sequential combinations of SBT and ARAC applied congruently and incongruently. Written informed consent was obtained from ten healthy, young subjects and all experiments were performed on the Computer Assisted Rehabilitation Environment (CAREN). Motion analysis was performed using infrared-reflective markers placed on the subjects’ lower limbs and ground reaction forces obtained from the force plates. Gait asymmetries were assessed for changes in step length, step time, and vertical reaction force and compared against baseline conditions. Between-trial comparisons were then performed using Friedman’s test and post-hoc analysis using Wilcoxon signed-rank test. Results Interference (during acquisition) to adaptation and memory consolidation (during retention) patterns exhibited different trends between opposite orders of intervention, and these characteristics were distinctive for step length and step time. Asymmetries during congruent trials were significantly greater than incongruent trials. SBT showed a greater influence (interference) on subsequent adaptation to ARAC than vice versa. Nonetheless, ARAC demonstrated a higher retention of after-effects than SBT – indicating its competitive potential for long-term learning. Conclusion The study shows that the order in which we learn to walk symmetrically can affect how well and how long we remember these skills. Based on the outcomes between different intervention order(s) on acquired asymmetries in step length and step time, future sequentially combined strategies can implement this sequence to balance minimizing interference between learning processes while maximizing consolidation of motor memories. This will help personalize future sequential interventions in terms of the targeted gait parameter and the costs acquired in other parameters to maximize the retained after-effects.