Elsevier

Gait & Posture

Volume 66, October 2018, Pages 107-113
Gait & Posture

The effect of center of pressure alteration on the ground reaction force during gait: A statistical model

https://doi.org/10.1016/j.gaitpost.2018.08.013Get rights and content

Highlights

  • Center of pressure manipulations significantly impact ground reaction force vectors.

  • Linear models correlating the center of pressure and the forces were exhibited.

  • The models can predict the three force components with good statistical significance.

  • Our results are significant for effective treatment using a robotic shoe.

  • Our results may also offer clinical implications in medical-shoe design industry.

Abstract

Background

Foot problems and lower-limb diseases (e.g., foot ulcers, osteoarthritis, etc.), are presented with a ground reaction force (GRF) that may deviate substantially from the normal. Thus, GRF manipulation is a key parameter when treating symptoms of these diseases. In the current study, we examined the impact of footwear-generated center of pressure (COP) manipulations on the GRF components, and the ability to predict this impact using statistical models.

Methods

A foot-worn biomechanical device which allows manual manipulation of the COP location was utilized. Twelve healthy young men underwent gait analysis with the device set to convey seven COP conditions: (1) a neutral condition, (2) lateral and (3) medial offset along the medio-lateral foot axis, (4) anterior and (5) posterior offset along the antero-posterior foot axis, and (6) a dorsi-flexion and (7) plantar-flexion condition. Changes in the magnitude and the early stance-phase impulse of the GRF components across COP conditions were observed. Linear models were used to describe relationships between COP conditions and GRF magnitude and impulse.

Results

With respect to ANOVA, the vertical and antero-posterior components of the GRF were significantly influenced by the COP configuration throughout the different stages of the stance-phase, whereas the medio-lateral components were not. The models of vertical, antero-posterior and medio-lateral GRF components were statistically significant.

Significance

The study results are valuable for the development of a method and means for efficient treatment of foot and lower-limb pathologies. The ability to predict and control the GRF components along three orthogonal axes, for a given COP location, provides a strong tool for efficient treatment of foot and lower-limb diseases and may also have relevant implications in sports shoe design. This study is a preliminary investigation for our ultimate goal to develop an effective treatment method by developing an autonomous GRF manipulations device based on closed-loop feedback.

Introduction

During gait, the foot is the point of physical contact between the environment and the body. As a result, the force acting on the foot, namely the three-dimensional ground reaction force (GRF), can simultaneously impact and be impacted by pathological disorders. Disorders such as degenerative diseases of the joints (e.g., osteoarthritis), injury, or foot problems (e.g., foot ulcers secondary to diabetes mellitus, plantar fasciitis) are presented with a GRF that may deviate substantially from the normal [1,2]. Thus, examination of the impact of external perturbations on the GRF may be of great interest in areas such as shoe design and footwear orthotics designed to treat symptoms of lower-limb joint and foot diseases.

The three-dimensional GRF is a reflection of the total mass-times-acceleration product of all body segments [3]. The origin of the GRF vector is the foot center of pressure (COP) which is a locus defined as the average location of all external forces acting between the foot and the ground [4]. Numerous studies have shown the correlation between external perturbations applied to the foot during gait and alteration of lower-limb biomechanics, including kinematics, kinetics, and neuro-muscular response [[5], [6], [7]]. The GRF, therefore, may be a key component when treating foot problems and lower-limb diseases.

In assessing impact of the GRF on the lower extremities, the lower limb is commonly viewed as a system of chained links, using the standard link-segment model, comprising a functional kinetic unit [8]. Applying the well-accepted method of inverse dynamics, to calculate moments and loads acting on the lower-limb joints, reveals that the GRF has far-reaching influence throughout the kinematic chain [9]. Devices currently used to treat foot and lower-limb pathologies are developed to optimize foot and joint loads [10,11]. However, in most existing devices the structure enabling modification of biomechanics is fixed, and thus does not enable GRF adjustments. Those few that enable modifications are typically adjusted only in low-frequency cycles (i.e., every few days due to the need of professional manual adjustment) and with no patient-specific biomechanics indicators. These limitations give rise to non-precise and uncontrolled fit of the device to the patient, leading to a potentially long and less effective treatment protocol.

In previous studies from our group, a foot-worn biomechanical device, composed of two adjustable convex rubber elements attached to the sole, allowing manipulation of the contact point between the device and the ground (i.e., COP), was used to manipulate lower-limb joint biomechanics. Adjustment of the elements impacts the COP trajectory by causing it to shift correspondingly [10,12], thereby having a direct effect on lower-limb biomechanics [5,13]. Among these studies are those exhibiting biomechanical and clinical benefit of specific perturbations in knee OA [14] and hip OA [15] populations, resulting in reduction of loads on the pathological joint, increase in functionality and quality of life, and decrease in pain [16]. The device in its current construction, however, requires manual calibration and subjective optimization of the device element positions by means of observational gait analysis of a trained physical therapist.

The ultimate goal, commencing with the present study, is to develop a footwear device for efficient treatment of lower-limb and foot pathologies by means of autonomous objective GRF manipulation. Our research group aims to develop a closed-loop feedback footwear device implementing external alterations of the three-dimensional GRF, and the ability to predict the impact of these alterations on foot and joint loading [17].

Several studies have shown that footwear-generated manipulation of the COP trajectory during gait leads to alteration of the GRF magnitude and orientation [18,19]. However, these studies were limited to COP modifications in the frontal plane only, and do not report the precise resulting alterations to the GRF and its three constituent components. Therefore, the objective of the present study was to examine the effect of footwear-generated COP manipulations along the medio-lateral and antero-posterior foot axes on the three-dimensional GRF vector components. We hypothesized that COP manipulation significantly influences the components of the GRF vector in a predictable manner that can be statistically modelled, and thus potentially used for precise footwear design, in general. The current study also serves as a preliminary investigation to assess the ability to control the GRF during gait in order to enable construction of the closed-loop feedback autonomous device.

Section snippets

Participants

Data acquired in a previous study, at the Biorobotics and Biomechanics Lab of the Faculty of Mechanical Engineering at the Technion - Israel Institute of Technology, focusing on impact of COP manipulation on the knee joint during gait [5] was utilized for the present analysis. The study group consisted of 12 healthy male subjects with a similar anthropometric and demographic profile (shoe size = French 43, dominant leg = right, age = 25.7 ± 2.1 years, height = 177.0 ± 3.8 cm,

Results

The one-way ANOVA revealed that speed did not change with change in COP configuration (p = 0.9882). Mean value of gait speed for each COP configuration is available in the supplemental material [Table S1]. With respective to the mixed effect ANOVA, the vertical and antero-posterior components of the GRF were significantly influenced by the COP configurations throughout the different stages of the stance phase, whereas the medio-lateral components were not. Mean and standard deviations of the

Discussion

In accordance with our hypothesis, we were able, with high statistical significance, to model and predict the behavior of the 3 GRF components throughout the entire stance phase, as well as impulse during early stance, in response to footwear-generated COP manipulations. The models show that several COP configurations impact certain gait event parameters more than others. Specifically, antero-posterior device element deviations impact 89% of the force events while medio-lateral and

Conflicts of interest

None.

Acknowledgment

The authors thank Apos Medical and Sports Technologies Ltd. for their generosity in contributing the devices used in the study.

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