Recovery from perturbation is highly individual and similar between different perturbation types and metrics: A dynamical systems perspective of flexibility in walking gait

BACKGROUND: Flexibility refers to how individuals can adopt alternative solutions to regain or maintain regular walking patterns when constraints are modified. Flexibility is an important yet still emerging characteristic of motor coordination. RESEARCH QUESTIONS: In walking gait, what are the characteristics of flexibility? METHODS: Twenty male participants (age 21-30) walked on a split-belt treadmill. Sudden perturbations in the form of belt accelerations or decelerations (direction) during mid-stance phase were applied at pseudo-random intervals (20-30 stride cycles). Kinematic data of the lower body were collected using Vicon motion capture. To represent flexibility, Continuous Relative Phase (CRP) variability was calculated for ankle-knee and knee-hip and pelvis-trunk couplings. The relaxation time of CRP variability after perturbation was used to evaluate the main effects of participant, successive perturbations, CRP coupling and perturbation direction. The relaxation time was considered as a component of how flexibility was channelled after perturbation. Repeated measures ANOVA and a univariate analysis was conducted to determine main effects on relaxation time. RESULTS: Significant main effects of participant and the effect of successive perturbations were observed, while CRP coupling and perturbation direction did not have an effect on relaxation time. SIGNIFICANCE: During perturbed walking on a treadmill, the response to perturbation was individual specific, a practice effect to the perturbation was present, and relaxation time did not differ by coupling or perturbation direction. This study provides a foundation for future studies to examine aspects of flexibility during walking, which can be applied to different participant populations.