Selective Reorganization of Reactive Gait Control: Interpreting Repeated Gait Perturbations Within the Framework of Locomotor Symmetry

Maintaining stability during walking requires rapid reactive adjustments to unexpected perturbations. Although repeated perturbations are known to induce locomotor adaptations, it remains unclear whether these changes reflect a generalized habituation of the locomotor system or selective modifications of specific biomechanical mechanisms. The aim of this study was to investigate changes in lower-limb kinematics, joint torques, and ground reaction force amplitudes during five consecutive treadmill-induced perturbations applied during the pre-swing phase of gait. Twenty-one healthy young women walked on an instrumented split-belt treadmill while five unilateral perturbations were applied to the left belt. For each perturbation, amplitudes of ankle, knee, and hip joint angles, joint torques, and ground reaction force components were calculated. Differences across perturbations were evaluated using Friedman repeated-measures analysis of variance followed by Bonferroni-corrected Wilcoxon tests. Significant effects of perturbation number were observed for hip joint angle amplitude, ankle joint torque amplitude, and anterior–posterior ground reaction force amplitude, whereas a weaker overall effect was detected for vertical ground reaction force amplitude. Hip angle amplitude decreased during later perturbations, whereas ankle torque and anterior–posterior ground reaction force amplitudes increased. No significant changes were found for knee and ankle joint angles, hip and knee joint torques, or mediolateral ground reaction force amplitude. These findings are consistent with the concept of locomotor symmetry as a theoretical framework for interpreting adaptive locomotor responses rather than as a directly measured outcome.