Changes in movement organization and control strategies when learning a biomechanically constrained gait pattern, racewalking: a PCA study

L Majed,A M Heugas,I A Siegler

doi:10.1007/s00221-016-4853-8

Abstract

Combining advances from gait analysis and motor learning fields, this study aims to examine invariant characteristics and practice-related changes in the control of walking gait when learning a biomechanically constrained pattern, racewalking (RW). RW’s regulation imposes a straightened knee at the stance phase which differentiates it qualitatively from normal walking. Using 3D motion analysis, we computed key kinematic variables from a whole-body model. Principal component analysis was then used as a tool to evaluate the evolution of normal walking synergies (S0) immediately at the first practice session (S1) and further with practice (S1–S4). Before the start of practice, normal walking was characterized by two predominant control dimensions explaining an upper-extremities/antero-posterior component (PC1) and a lower-extremities/vertical component (PC2). Compared to normal walking, the immediate increase at S1 in the number of PCs needed to explain a significant portion of movement variance could be suggestive of a recruitment of a task-specific component. With practice, the significant decrease in the variance accounted for by PC1 and in the correlations between many variables could indicate a destabilization of spontaneous tendencies to facilitate the adoption of more task-specific coordinative pattern. PC2 seemed to be reinforced with practice where a significant increase in its explained variance was observed. In sum, this study shows that common features in the gait control are preserved with practice, and the movement reorganization, however, seems rather defined by shifts in the relative contribution of some variables within each PC.

Highlights

The apparent simplicity of producing whole-body actions, like walking for instance, hides underlying complex processes in which the many redundant degrees of freedom (DoF) need to be coordinated and controlled (Bernstein 1967; Newell 1986)
For the majority of participants at S0, it is clear that PC1 included motions of the arm, hip, shoulder, pelvis and elbow, and PC2 encompassed the knee motion and pelvis
This study challenged to identify common control strategies in movement reorganization when learning the biomechanical constraints of a differentiated gait pattern by using principal component analysis (PCA)

Summary

Introduction

The apparent simplicity of producing whole-body actions, like walking for instance, hides underlying complex processes in which the many redundant degrees of freedom (DoF) need to be coordinated and controlled (Bernstein 1967; Newell 1986). Several studies have examined the existence of invariant principles in the organization of mechanical DoF by studying kinematic properties of body joints and segments’ spatial configurations (Vereijken et al 1992; Temprado et al 1997; Caillou et al 2002; Majed et al 2012). The “freezing-releasing” strategy (Bernstein 1967) suggests an initial “freezing” of the DoF, understood as rigid couplings between the latter to reduce the complexity problem. Progression in skill is associated with a release of the constraints imposed early in practice (i.e., freezing) organizing the DoF into coordinated action. Considerable advances have been made in that field, taken together, studies failed to generalize on invariant features of movement control with skill acquisition given the importance of task-specific and environmental constraints (Newell and Vaillancourt 2001; Exp Brain Res (2017) 235:931–940

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