Effects of Different Low-Density Insoles on Foot Activation Time at Different Walking Speeds in Young Females

Research Article

Phys Med Rehabil Int. 2018;5(2): 1142.

Effects of Different Low-Density Insoles on Foot Activation Time at Different Walking Speeds in Young Females

Güner S*, Alsancak S, Altinkaynak H, Güven E,özgün K and Aytekin G

1Department of Prosthetics and Orthotics, Vocational School of Health Services, Ankara University, Ankara, Turkey

*Corresponding author: Senem Güner, Prosthetics and Orthotics Department, Vocational School of Health, Ankara University, Fatih Street 197/A, 06290 Kecioren, Ankara, Turkey

Received: February 26, 2018; Accepted: March 22, 2018; Published: March 29, 2018

Abstract

Aim: Shoes for walking and other locomotor activities provide the only interaction between the body and the ground; therefore, shoes are typically constructed to provide stability and comfort to the user. However, studies investigating the optimal shoe insole material, particularly for flat shoes, based on different walking speeds are limited. Therefore, the purpose of this study was to evaluate the foot activation time using different low-density insole material and walking speed combinations.

Methods: Twelve healthy females participated in this study. The activation time measurements were obtained using 8 WalkinSense sensors in each trial and exported from the proprietary software (WalkinSense version 0.96, Tomorrow Options Microelectronics, S.A). Each subject underwent the same testing procedure on a treadmill (i.e., slow, normal and fast walking speeds) first without the insole and then in shoes with Insole I (6-mm flat noraLunatec EP insole), Insole II (6-mm flat nora Astro form 8 insole) and Insole III (6-mm flat nora Aero sorb M insole).

Results: The percentage of activation time was significantly higher under the fast walking condition than under the slow walking condition in the hallux with the shoe only, Insole I, Insole II and Insole III (p<0.05). The activation time of the lateral heel was significantly higher under the slow walking condition than under the fast walking condition with the shoe only, Insole I and Insole II. The activation time of the medial heel was significantly higher under the slow walking condition than under the fast walking condition with the shoe only, Insole I, Insole II and Insole III (p<0.05). The percentage of the activation time of the lateral midfoot was significantly lower under the shoe only condition than under the Insole II and Insole III conditions during slow walking.

Conclusion: Lower-density insoles may positively affect the loading activation time in the lateral midfoot. Custom-made insole surfaces produced with low-density material may be suitable for fast walking in people with flat shoes.

Keywords: Flat shoes; Insole material; Foot activation time

Introduction

Plantar loading evaluations are frequently used to assess the effectiveness of an insole in reducing the risk factors for soft-tissue mechanical trauma associated with weight-bearing activities of daily living. When the plantar pressure is reduced, the force is distributed over a larger area [1]. The materials used to fabricate insoles have been shown to improve the plantar pressure, reduce shock, and enhance comfort [2,3]. Pratt et al. quasi-quantitatively evaluated the shockabsorbing characteristics of Plastazote, Spenco, Sorbothane, Poron and Viscolas. Poron was rated the best insole material for shock absorption [4,5]. Leber and Evanski investigated 26 participants who complained of forefoot pain upon bearing weight, and all participants exhibited areas of increased pressure under one or more metatarsal heads when tested. While all materials tested reduced the overall plantar pressure compared to that under the barefoot condition, the authors ranked the materials as follows: PPT (an open cell, porous, firm foam material), Plastazote (foamed polyethylene material with a closed-cell structure) and Spenco (a neoprene sponge product with nitrogen-induced closed cells covered with a multi stretch nylon fabric on one side) were the most effective; Dynafoam (a polyvinyl chloride foam compound) was somewhat effective; and Ortho felt (a resilient fabric composed of a cotton-wool blend with a relatively low tensile strength) and latex foam (a cellular rubber material with an open-cell structure) were the least effective [6]. Gillespie and Dickey developed a filter bank procedure to determine the effectiveness of different foot orthotic materials. The materials were found to reduce the initial peak force, loading rate and frequency of transient impact during walking, and Plastazote was the most effective material for attenuating the high-frequency component of the initial ground reaction force during walking [7].

Ethylene-vinyl acetate (EVA) is a highly elastic copolymer with ethylene and vinyl acetate sintered to form a porous material similar to rubber but with excellent toughness. The porous elastomeric characteristic of EVA is much more flexible than that of low-density polyethylene, which is commonly used in shoe construction; due to its resistance, flexibility, and temperature toughness properties, EVA is among the most used copolymers in shoe midsole construction. The addition of EVA to elastomers could lead to the ideal softness and high resilience characteristics needed for a full-recovery capacity in the next foot step after a heel strike, while a less resilient (more viscous) material could attenuate more energy during the initial loading cycles, easily achieving compression flattening after some cycles [8,9].

Numerous studies have examined the plantar pressure during walking at different speeds, both barefoot and in shoes [10-15]. According to these studies, increasing the walking speed results in an increased plantar pressure in each of the foot regions examined [10,14]. The walking speed has been shown to linearly influence the loading patterns beneath the hallux and rear foot; however, the increases in the walking speed had a lower impact on the forefoot loading patterns [10,14-16]. Medial forefoot loading initially increases at slower walking speeds; however, the medial forefoot loading remains constant or decreases as individuals begin to walk faster, which is attributed to a decrease in the contact time as the walking speed increases [10]. While changes in the loading patterns have been observed in the hindfoot, hallux and forefoot, the forces beneath the medial and lateral midfoot were not significantly altered as the walking speed increased [14]. In addition to examining the influence of the walking speed, previous studies have examined the effect of different footwear on the plantar pressure patterns; the plantar pressure is significantly lower in participants walking in running shoes than in participants walking barefoot [14,17]. In contrast to studies examining plantar pressure distribution patterns during walking, very few studies have examined plantar pressure distribution patterns during running. Burnfield et al. examined the differences in plantar loading at different walking speeds [14] and found that as the walking speed increased, the plantar loading also increased.

Thus, the purpose of our study was to determine the effects of different insole material and walking speed combinations on the foot activation time under the hindfoot, midfoot, and forefoot plantar surface areas in individuals with normal feet. We hypothesized that a decrease in the insole density could increase the activation time distribution on the foot during fast walking.

Methods

Subjects

In total, 12 healthy female participants with an average age, weight, and height of 20.16, 54.7 kg and 159.7cm, respectively, without any known history of diseases or foot pathologies were recruited for this study. All subjects were undergraduate students at a local university. Ethical approval was obtained from University High School Committee. Written informed consent was obtained from the volunteers before the measurements were performed. The inclusion criteria included volunteers with no known diseases or foot deformities, who had the ability to walk on a treadmill independently without assistance or any walking aids. Participants with the following foot deformities were excluded: pes planus, pes cavus, plantar heel pain, metatarsalgia, hallux valgus/varus/limitus/rigidus and lesser toe deformities, such as hammer toes, clawed toes and mallet toes. The demographic data, including the ages, heights and weights of the subjects, were recorded. This study used flat shoes because these shoes are more popular and widely used than high heel shoes among university-aged women.

Activation time measurements

The activation time was calculated as a percentage of the walking cycle. The activation time measurements were performed using 8 WalkinSense sensors in each trial and exported from the proprietary software (WalkinSense version 0.96, Tomorrow Options Microelectronics, S.A.) [18]. The system consisted of a data acquisition and processing unit and eight individual sensors attached to the participants’ socks to measure the plantar pressure and activation time (Figure 1). The participants wore standard shoes and socks, which were fitted with the WalkinSense sensors and provided to the participants. The order of the trials without an insole and the three insoles (I, II and III) was counterbalanced in this study (Figure 2).

Figure 1: WalkinSense-system.

    

    
    

    

    Figure 1:  WalkinSense-system.

Figure 2: Flat- shoes and Insole I, Insole II, Insole III.

    

    
    

    

    Figure 2:  Flat- shoes and Insole I, Insole II, Insole III.

Insole material

This study consisted of the following 4 testing conditions involving participants walking on a treadmillShoes only: Shoes with a heel height of 0.8 mm and flat, thin, high-density polyurethane 0.4- mm outsoles.