Elsevier

Gait & Posture

Volume 42, Issue 2, July 2015, Pages 214-217
Gait & Posture

Short Communication
Can toe-ground footwear margin alter swing-foot ground clearance?

https://doi.org/10.1016/j.gaitpost.2015.05.013Get rights and content

Highlights

  • Vertical margin of the toe part of a shoe from the floor influences tripping risks.

  • Virtual marker function can simulate gait kinematics for shoe-designs.

  • Dorsiflexion is the key ankle joint motion to increase swing foot-ground clearance.

Abstract

Falls are an important healthcare concern in the older population and tripping is the primary cause. Greater swing foot-ground clearance is functional for tripping prevention. Trips frequently occur due to the lowest part of the shoe contacting the walking surface. Shoe design effects on swing foot-ground clearance are, therefore, important considerations. When a shoe is placed on a flat surface, there usually is small vertical margin (VM) between the walking surface and the minimum toe point (MTP). The current study examined the effects of VM on swing foot-ground clearance at a critical gait cycle event, minimum foot clearance (MFC). 3D coordinates of the swing foot (i.e. MTP and heel) were obtained during the swing phase. MTP represented the swing foot-ground clearance and various MTPs were modelled based on a range of VMs. The sagittal orientation of the toe and heel relative to the walking surface was also considered to evaluate effects of VM and swing foot angle on foot-ground clearance. Greater VM increased the swing foot-ground clearance. At MFC, for example, 0.09 cm increase was estimated for every 0.1 cm VM. Foot angle throughout the swing phase was typically −30° and 70°. Increasing swing ankle dorsiflexion can maximise VM, which is effective for tripping prevention. Further research will be needed to determine the maximum thresholds of VM to be safely incorporated into a shoe.

Introduction

Tripping is the leading cause of falls sustained by older adults when walking [1]. Tripping is defined biomechanically as an event at which the most distal feature of the swing limb, usually the lowest part of the shoe, makes unanticipated contact with either the supporting surface or objects on it with sufficient force to destabilise the walker [2]. The risk of a tripping-associated fall is considered highest at minimum foot clearance (MFC), the mid-swing phase event at which the vertical displacement of swing foot from the walking surface is minimal [2], [3], [4].

Maintaining adequate MFC is, therefore, fundamental for tripping prevention [3]. Ankle dorsiflexion is the most effective lower limb joint angle modulation because a relatively small ankle angle change can considerably influence MFC with minimum disruption to gait control [5]. Few falls prevention strategies have, however, specifically targeted tripping-related falls.

Footwear design is an emerging consideration for safe outdoor walking to maintain the mobility of older adults [6]. The aim of this current study was to determine the effects of shoe forefoot design on foot-ground clearance. Minimum toe point (MTP) is the minimum vertical displacement of the swing toe at MFC (Fig. 1A). On a flat walking surface, most shoes provide a small vertical margin (VM) to MTP. In this paper effects of increased VM on swing foot-ground clearance were modelled using the virtual marker function [7].

To evaluate VM effects on swing foot-ground clearance, sagittal swing foot orientation was defined by the toe-heel angle relative to the horizontal. Given a typical sagittal ankle orientation at MFC the toe is lower than the heel. Based on the previous study [8], greater VM is hypothesised to increase foot-ground clearance. When the swing foot is parallel to the walking surface VM effects on increased swing foot-ground clearance are maximised (Fig. 1). Greater VM was, therefore, hypothesised to increase swing foot-ground clearance by aligning the shoe (operationally the toe rigid body) more parallel to the walking surface at MFC.

Section snippets

Data collection

A total of 150 right swing phase cycles (i.e. from toe-off to heel contact) of five healthy young males (height: 1.77 ± 0.07 m, body mass: 72.6 ± 14.0 kg) were analysed using three Optotrak Certus (Northern Digital Inc.) motion analysis camera units surrounding an 8 m walkway. The cameras sampled the two rigid bodies, each comprising 3 infrared light emitting diodes (100 Hz). The rigid bodies provided the position-time data to calculate sagittal plane kinematics of the right foot MTP and heel during

Results

Swing foot-ground clearances corresponding to the modelled values of VM = 0.2 cm and VM = 1.1 cm are described in Fig. 2(top). Effects of a 0.1 cm increase in VM on swing foot clearances over the swing phase were: +0.05 cm at toe-off; +0.06 cm at Mx1; +0.09 cm at MFC; +0.08 cm at Mx2 and +0.09 cm at heel contact (Fig. 2, bottom).

Fig. 3B visualises foot angle throughout the swing phase. Foot angle was greatest near toe-off but reduced to zero following MFC when the toe and heel were at the same height.

Discussion

Various shoe features have been investigated previously [6]. The current study demonstrated that vertical toe-height when standing (VM) combined with foot angle are important determinants of swing foot-ground clearance including the critical MFC event. Consistent with the experimental data [8], the current simulation confirmed that greater VM increases swing foot-ground clearance for a typical swing foot angle i.e., −90° < α < +90° (Fig. 3B) [4]. In relation to VM, smaller swing foot angle until

Conflict of interest statement

The authors do not declare any conflict of interest.

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