Elsevier

Gait & Posture

Volume 56, July 2017, Pages 49-53
Gait & Posture

Short communication
Constituent Lower Extremity Work (CLEW) approach: A novel tool to visualize joint and segment work

https://doi.org/10.1016/j.gaitpost.2017.04.024Get rights and content

Highlights

  • A proposed approach to evaluate relative lower extremity work.

  • The approach summarizes constituent (joint & segment) work over a cyclic task.

  • A novel clinically compatible report to visualize this approach is presented.

Abstract

Work can reveal the mechanism by which movements occur. However, work is less physically intuitive than more common clinical variables such as joint angles, and are scalar quantities which do not have a direction. Therefore, there is a need for a clearly reported and comprehensively calculated approach to easily visualize and facilitate the interpretation of work variables in a clinical setting. We propose the Constituent Lower Extremity Work (CLEW) approach, a general methodology to visualize and interpret cyclic tasks performed by the lower limbs. Using six degree-of-freedom power calculations, we calculated the relative work of the four lower limb constituents (hip, knee, ankle, and distal foot). In a single pie chart, the CLEW approach details the mechanical cost-of-transport, the percentage of positive and negative work performed in stance phase and swing phase, and the individual contributions of positive and negative work from each constituent. This approach can be used to compare the constituent-level adaptations occurring between limbs of individuals with impairments, or within a limb at different gait intensities. In this article, we outline how to generate and interpret the CLEW pie charts in a clinical report. As an example of the utility of the approach, we created a CLEW report using average reference data from eight unimpaired adult subjects walking on a treadmill at 0.8 statures/s (1.4 m/s) compared with data from the intact and prosthetic limbs of an individual with a unilateral amputation walking with an above-knee passive prosthesis.

Introduction

Several researchers have used the principles of energetics to explain the compensatory strategies used by individuals with impairments (e.g., [1], [2], [3]). Relative joint work, or the comparative amount each joint's work contributed to absolute limb work, can reveal the primary limb “drivers” (positive) and “brakers” (negative) during a movement task like walking. However, work is less physically intuitive than more common clinical variables such as joint angles, partly because it is a scalar quantity which does not have a direction.

Previously, researchers have reported the work generated (positive) and absorbed (negative) by each of the joints using line [1], [4] and bar charts [5]. While these graphs can be used to compare joint work across gait intensity and between limbs of the same joint at one intensity, the overlapping lines and error bars can be confusing to interpret. There is a need for a clearly reported approach to visualize and facilitate the interpretation of work variables in a clinical setting.

The objective of this article is to introduce the Constituent Lower Extremity Work (CLEW) approach, a general methodology to visualize and interpret cyclic tasks performed by the lower limbs. The term “constituents” will be used to refer to the hip, knee, ankle, and distal foot of the limb. The utility of this tool is demonstrated by presenting a report with the relative work of the four lower limb constituents in both limbs of a sample of healthy, unimpaired individuals and in the prosthetic and intact limbs of an individual with a unilateral amputation walking on a treadmill.

Section snippets

Methods

As a representative case study, data were collected from an adult individual (height 1.68 m, mass 79.15 kg) walking on an instrumented treadmill (Bertec Corp., Columbus, OH) who required use of an above-knee prosthesis due to a congenital proximal femoral focal deficiency. Reflective markers were positioned using a modification of a six-degree-of-freedom (6-DOF) marker set [6]. A seven-camera motion capture system was used to collect kinematic data (Motion Analysis, Santa Rosa, CA). Motion

Results

Average net 6-DOF limb work, absolute 6-DOF limb work, stride length, and cost-of-transport are all reported in Table 1 for the left and right limbs of the unimpaired individuals (mean ± standard deviation) and the individual with amputation (hereafter noted as subject data). Fig. 2 depicts a typical clinical CLEW report. Fig. 2A summarizes the steps for systematically evaluating a subject's CLEW pie chart and a short interpretation of each variable. Fig. 2B provides an example of a typical CLEW

Discussion

The purpose of this study was to introduce the CLEW approach and demonstrate its utility in quantifying relative constituent work in a succinct and visually informative manner. The size of the pie charts, representing the mechanical cost-of-transport, provides a spatial relationship to interpret the total burden of work for the limb. The designation of positive and negative relative constituent work provides a way to readily compare the contribution of work from each constituent during the

Conflict of interest statement

The authors have no financial or personal relationships with individuals or organizations that inappropriately influenced this work.

Acknowledgments

This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1247394 and by the University of Delaware College of Health Sciences and Mechanical Engineering departments. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. This project was also supported by the BADER consortium, a Department of

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