Postural Organization of Gait Initiation for Biomechanical Analysis Using Force Platform Recordings

Summary

This paper describes the material and method developed to investigate the postural organization of gait initiation. The method is based on force platform recordings and on the direct principle of mechanics to compute center of gravity and center of pressure kinematics.

Abstract

Gait initiation (GI), the transient phase between orthograde posture and steady-state locomotion, is a functional task and an experimental paradigm that is classically used in the literature to obtain insight into the basic postural mechanisms underlying body motion and balance control. Investigating GI has also contributed to a better understanding of the physiopathology of postural disorders in elderly and neurological participants (e.g., patients with Parkinson's disease). As such, it is recognized to have important clinical implications, especially in terms of fall prevention.

This paper aims to provide scholars, clinicians, and higher education students information on the material and method developed to investigate GI postural organization via a biomechanical approach. The method is based on force platform recordings and the direct principle of mechanics to compute the kinematics of the center of gravity and center of pressure. The interaction between these two virtual points is a key element in this method since it determines the conditions of stability and whole-body progression. The protocol involves the participant initially standing immobile in an upright posture and starting to walk until the end of an at least 5 m track.

It is recommended to vary the GI velocity (slow, spontaneous, fast) and the level of temporal pressure - gait may be initiated as soon as possible after the deliverance of a departure signal (high level of temporal pressure) or when the participant feels ready (low level of temporal pressure). Biomechanical parameters obtained with this method (e.g., duration and amplitude of anticipatory postural adjustments, step length/width, performance, and stability) are defined, and their computation method is detailed. In addition, typical values obtained in healthy young adults are provided. Finally, critical steps, limitations, and significance of the method with respect to the alternative method (motion capture system) are discussed.

Introduction

Gait initiation (GI), the transient phase between orthograde posture and steady-state locomotion, is a functional task and an experimental paradigm that is classically used in the literature to investigate postural control during a complex motor task requiring simultaneous whole-body propulsion and stability¹. Patients with neurological conditions, such as Parkinson's disease², stroke³, progressive supranuclear palsy⁴, and "higher level gait disorders"⁵, are known to have difficulty initiating gait, which exposes them to an increased risk....

Protocol

The protocol described below follows the guideline of the human research ethics committee of the Université Paris-Saclay. Participants approved and signed a consent form.

1. Participants

1. Include at least 15 healthy young adult participants in the experiment (aged 20 to 40 years old).
   NOTE: This recommended number of subjects corresponds to what is classically considered in the literature on GI.
2. Exclude participants with walking aids, visual, hearing, or orthopedic problems, identified neurological disorders, dementia, cognitive impairments (i.e., a score < 25 on the Mini Mental State Exam), and a ....

Results

Description of representative biomechanical time plots obtained from the force platform during gait initiation
Whatever the level of temporal pressure or the instruction on GI velocity, swing heel-off is systematically preceded by APA. These APA can be characterized by a backward and swing leg side shift of the center of pressure (Figure 2). This anticipatory center of pressure shift promotes the acceleration of the center of gravity in the opposite direction (i.e., forw.......

Discussion

The goal of this paper was to provide scholars, clinicians, and higher education students information on the method (the "global" method) used in our laboratory to investigate the biomechanical organization of gait initiation (GI). Critical steps of the protocol, limitations of the method, and alternative methods and applications are discussed below.

A critical step in the protocol is the detection of the timing events of GI (i.e., APA onset, swing heel-off and toe-off, and rear foot-o.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Force platform(s)	AMTI		One large [120 cm x 60 cm] or two small [60 cm x 40 cm] force platform(s)
Python or Matlab	Python or MathWorks		Programming language for the computation of experimental variables
Qualisys track manage	Qualisys		Software for the synchronization of the force platform(s), the recording and the on-line visualization of raw biomechanical traces (3D forces and moments)
Visual3D	C-Motion Inc		Software for the processing of raw biomechanical traces (low-pass filtering)