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v
Contents
About Dynamics of Human Gait vii
About Gait Analysis Laboratory ix
Acknowledgments xi
Chapter 1 In Search of the Homunculus 1
Top-Down Analysis of Gait 2
Measurements and the Inverse Approach 4
Summary 6
Chapter 2 The Three-Dimensional and Cyclic Nature of Gait 7
Periodicity of Gait 8
Parameters of Gait 12
Summary 14
Chapter 3 Integration of Anthropometry, Displacements,
and Ground Reaction Forces 15
Body Segment Parameters 16
Linear Kinematics 22
Centres of Gravity 29
Angular Kinematics 32
Dynamics of Joints 36
Summary 43
Chapter 4 Muscle Actions Revealed Through Electromyography 45
Back to Basics 45
Phasic Behaviour of Muscles 52
Relationship Between Different Muscles 55
Summary 62
Chapter 5 Clinical Gait Analysis  A Case Study 63
Experimental Methods 64
Results and Discussion 65
Summary 76
vi
Appendix A Dynamic Animation Sequences 77
Appendix B Detailed Mathematics Used in GaitLab 83
Appendix C Commercial Equipment for Gait Analysis 107
References 133
Index 137
CONTENTS
vii
About Dynamics
of Human Gait
This book was created as a companion to the GaitLab software package.
Our intent was to introduce gait analysis, not to provide a comprehensive
guide. We try to serve readers with diverse experience and areas of interest
by discussing the basics of human gait as well as some of the theoretical,
biomechanical, and clinical aspects.
In chapter 1 we take you in search of the homunculus, the little being
inside each of us who makes our walking patterns unique. We represent the
walking human as a series of interconnected systems  neural, muscular,
skeletal, mechanical, and anthropometric  that form the framework for
detailed gait analysis.
The three-dimensional and cyclical nature of human gait is described in
chapter 2. We also explain how many of the relevant parameters can be
expressed as a function of the gait cycle, including kinematics (e.g., height of
lateral malleolus), kinetics (e.g., vertical ground reaction force), and muscle
activity (e.g., EMG of rectus femoris).
In chapter 3 we show you how to use the framework constructed in the
first two chapters to integrate anthropometric, 3-D kinematic, and 3-D force
plate data. For most readers this will be an important chapter  it is here
that we suggest many of the conventions we believe to be lacking in three-
dimensional gait analysis. Although conceptually rigorous, the mathemati-
cal details are kept to a minimum to make the material accessible to all stu-
dents of human motion. (For the purists interested in these details, that infor-
mation is in Appendix B.)
In chapter 4 we describe the basics of electromyography (EMG) and how
it reveals the actions of the various muscle groups. We discuss some of the
techniques involved and then illustrate the phasic behaviour of muscles dur-
ing the gait cycle and describe how these signals may be statistically analysed.
One of the purposes of this book is to help clinicians assess the gaits of
their patients. Chapter 5 presents a case study of a 23 year-old-man with
cerebral palsy. We have a complete set of 3-D data for him that can be
processed and analyzed in GaitLab.
Beginning in Appendix A we use illustrated animation sequences to em-
phasize the dynamic nature of human gait. By carefully fanning the pages of
viii
the appendixes, you can get a feel for the way the human body integrates
muscle activity, joint moments, and ground reaction forces to produce a
repeatable gait pattern. These sequences bring the walking subject to life
and should provide you with new insights.
The detailed mathematics used to integrate anthropometry, kinematics,
and force plate data and to generate 3-D segment orientations, and 3-D joint
forces and moments are presented in Appendix B. This material, which is
the basis for the mathematical routines used in GaitLab, has been included
for the sake of completeness. It is intended for researchers who may choose
to include some of the equations and procedures in their own work.
The various pieces of commercially available equipment that may be used
in gait analysis are described and compared in Appendix C. This summary
has been gleaned from the World Wide Web in late 1998 and you should be
aware that the information can date quite rapidly.
Dynamics of Human Gait provides a solid foundation for those new to
gait analysis, while at the same time addressing advanced mathematical tech-
niques used for computer modelling and clinical study. As the first part of
Gait Analysis Laboratory, the book should act as a primer for your explora-
tion within the GaitLab environment. We trust you will find the material
both innovative and informative.
ABOUT DYNAMICS OF HUMAN GAIT
ix
About Gait Analysis
Laboratory
Gait Analysis Laboratory has its origins in the Department of Biomedical
Engineering of Groote Schuur Hospital and the University of Cape Town. It
was in the early 1980s that the three of us first met to collaborate on the
study of human walking. Our initial efforts were simple and crude. Our
two-dimensional analysis of children with cerebral palsy and nondisabled
adults was performed with a movie camera, followed by tedious manual
digitizing of film in an awkward minicomputer environment. We concluded
that others travelling this road should have access  on a personal com-
puter  to material that conveys the essential three-dimensional and dy-
namic nature of human gait. This package is a result of that early thinking
and research.
There are three parts to Gait Analysis Laboratory: this book, Dynamics of
Human Gait, the GaitLab software, and the instruction manual on the inside
cover of the CD-ROM jewel case. In the book we establish a framework of
gait analysis and explain our theories and techniques. One of the notable
features is the detailed animation sequence that begins in Appendix A. These
walking figures are analogue counterparts to the digital animation presented
in Animate, the Windows 95 software that is one of the applications in the
GaitCD package. GaitLabs sizable data base lets you explore and plot more
than 250 combinations of the basic parameters used in gait analysis. These
can be displayed in a variety of combinations, both graphically and with stick
figure animation.
Weve prepared this package with the needs of all students of human move-
ment in mind. Our primary objective has been to make the theory and tools
of 3D gait analysis available to the person with a basic knowledge of me-
chanics and anatomy and access to a personal computer equipped with Win-
dows 95. In this way we believe that this package will appeal to a wide
audience. In particular, the material should be of interest to the following
groups:
 Students and teachers in exercise science and physiotherapy
 Clinicians in orthopaedic surgery, physiotherapy, podiatry,
x
rehabilitation, neurology, and sports medicine
 Researchers in biomechanics, kinesiology, biomedical engineering, and
the movement sciences in general
Whatever your specific area of interest, after working with Gait Analysis
Laboratory you should have a much greater appreciation for the human lo-
comotor apparatus, particularly how we all manage to coordinate move-
ment in three dimensions. These powerful yet affordable tools were de-
signed to provide new levels of access to the complex data generated by a
modern gait analysis laboratory. By making this technology available we
hope to deepen your understanding of the dynamics of human gait.
ABOUT GAIT ANALYSIS LABORATORY
xi
Acknowledgements
First Edition
We are grateful to all those who have enabled us to add some diversity to our
book. It is a pleasure to acknowledge the assistance of Dr. Peter Cavanagh,
director of the Center for Locomotion Studies (CELOS) at Pennsylvania
State University, who provided the plantar pressure data used for our anima-
tion sequence, and Mr. Ron Ervin, who drew the human figures used in the
sequence.
Dr. Andreas von Recum, professor and head of the Department of Bioengi-
neering at Clemson University, and Dr. Michael Sussman, chief of Paediatric
Orthopaedics at the University of Virginia, provided facilities, financial sup-
port, and substantial encouragement during the writing of the text.
The three reviewers, Dr. Murali Kadaba of Helen Hayes Hospital, Dr.
Stephen Messier of Wake Forest University, and Dr. Cheryl Riegger of the
University of North Carolina, gave us substantial feedback. Their many sug-
gestions and their hard work and insights have helped us to make this a
better book.
We are especially grateful to Mrs. Nancy Looney and Mrs. Lori White,
who helped with the early preparation of the manuscript.
Appendix C, Commercial Equipment for Gait Analysis, could not have
been undertaken without the interest and cooperation of the companies men-
tioned.
The major thrust of Gait Analysis Laboratory, the development of GaitLab,
took place in June and July of 1988 in Cape Town. We especially thank Dr.
George Jaros, professor and head of the Department of Biomedical Engi-
neering at the University of Cape Town and Groote Schuur Hospital. He
established an environment where creativity and collaboration flourished.
We also acknowledge the financial support provided by the university, the
hospital, and the South African Medical Research Council.
Much of the conceptual framework for Gait Analysis Laboratory was de-
veloped during 1983-84 in England at the University of Oxfords Ortho-
paedic Engineering Centre (OOEC). Dr. Michael Whittle, deputy director,
and Dr. Ros Jefferson, mathematician, provided insight and encouragement
during this time. They have maintained an interest in our work and recently
shared some of their kinematic and force plate data, which are included in
GaitLab.
The data in chapters 3 and 5 were provided by Dr. Steven Stanhope, direc-
tor, and Mr. Tom Kepple, research scientist, of the Biomechanics Labora-
tory at the National Institutes of Health in Bethesda, Maryland; and by Mr.
xii
George Gorton, technical director, and Ms. Patty Payne, research physical
therapist, of the Motion Analysis Laboratory at the Childrens Hospital in
Richmond, Virginia. Valuable assistance was rendered by Mr. Francisco
Sepulveda, graduate student in bioengineering, in the gathering and analysis
of the clinical data.
Finally, it is a pleasure to acknowledge the efforts of the staff at Human
Kinetics. We make special mention of Dr. Rainer Martens, publisher, Dr.
Rick Frey, director of HK Academic Book Division, and Ms. Marie Roy and
Mr. Larret Galasyn-Wright, developmental editors, who have been enthusi-
astic, supportive, and above all, patient.
Second Edition
Since the first edition was published seven years ago, there have been other
people who have provided significant input to this second edition.
At the University of Virginia, from 1992-1995, the Motion Analysis Labo-
ratory provided an important intellectual home. Ms. Stephanie Goar, labo-
ratory manager, assisted with the preparation of the revised manuscript and
updated the references in the GaitBib database. Dr. Gary Brooking and Mr.
Robert Abramczyk, laboratory engineers, were responsible for gathering and
tracking the expanded set of clinical data files used by the latest version of
GaitLab. The database of 3D kinematic and force plate data for normal
children was assembled by Mr. Scott Colby, graduate student in biomedical
engineering. Mr. Scott Seastrand, architectural student, converted all the
original artwork into computer format for this electronic version of Dynam-
ics of Human Gait. Two fellow faculty members at the University of Vir-
ginia  Dr. Diane Damiano, physical therapist, and Dr. Mark Abel, ortho-
paedic surgeon  provided important insights regarding the clinical applica-
tions of gait analysis, especially applied to children with cerebral palsy.
By 1996 the wheel had turned full circle and Dr. Kit Vaughan returned to
the University of Cape Town where he re-established contact with Mr. Jer-
emy OConnor. In the Department of Biomedical Engineering, and with the
financial support of the Harry Crossley Foundation and the South African
Foundation for Research Development, the project continued. Computer
programming support was provided by Ms. Michelle Kuttel, graduate stu-
dent in computer science and chemistry, and Mr. Mark de Reus, graduate
student in biomedical engineering. Preparation of the appendices in Dynam-
ics of Human Gait was done by Mrs. Cathy Hole, information specialist, and
Ms. Narima Panday, senior secretary. The desktop publishing of the whole
of Dynamics of Human Gait was performed by Mr. Roumen Georgiev, gradu-
ate student in biomedical engineering.
Finally, it is a pleasure to acknowledge the contribution of Mr. Edmund
Cramp of Motion Lab Systems in Baton Rouge, Louisiana, who provided us
with the software tools to translate binary format C3D files into the text-
based DST files used by the GaitLab package.
ACKNOWLEDGMENTS
IN SEARCH OF THE HOMUNCULUS 1
In Search of
the Homunculus
Homunculus: An exceedingly minute body that according to
medical scientists of the 16th and 17th centuries, was contained
in a sex cell and whose preformed structure formed the basis for
the human body.
Stedmans Medical Dictionary
When we think about the way in which the human body walks, the analogy of a
marionette springs to mind. Perhaps the puppeteer who pulls the strings and
controls our movements is a homunculus, a supreme commander of our locomo-
tor program. Figure 1.1, reprinted from Inman, Ralston, and Todd (1981), illus-
trates this point in a rather humorous but revealing way. Though it seems simplis-
tic, we can build on this idea and create a structural framework or model that will
help us to understand the way gait analysis should be performed.
1
CHAPTER 1
Figure1.1 A homun-
culus controls the
dorsiflexors and plantar
flexors of the ankle, and
thus determines the
pathway of the knee.
Note. From Human
Walking (p. 11) by V.T.
Inman, H.J. Ralston,
and F. Todd , 1981,
Baltimore: Williams &
Wilkins. Copyright
1981 by Williams &
Wilkins. Reprinted by
permission.
2 DYNAMICS OF HUMAN GAIT
Top-Down Analysis of Gait
Dynamics of Human Gait takes a top-down approach to the description of
human gait. The process that we are most interested in starts as a nerve
impulse in the central nervous system and ends with the generation of ground
reaction forces. The key feature of this approach is that it is based on cause
and effect.
Sequence of Gait-Related Processes
We need to recognise that locomotor programming occurs in supraspinal
centres and involves the conversion of an idea into the pattern of muscle activity
that is necessary for walking (Enoka, 1988). The neural output that results
from this supraspinal programming may be thought of as a central locomotor
command being transmitted to the brainstem and spinal cord. The execution
of this command involves two components:
1. Activation of the lower neural centres, which subsequently establish
the sequence of muscle activation patterns
2. Sensory feedback from muscles, joints, and other receptors that
modifies the movements
This interaction between the central nervous system, peripheral nervous system,
and musculoskeletal effector system is illustrated in Figure 1.2 (Jacobsen &
Webster, 1977). For the sake of clarity, the feedback loops have not been
included in this figure. The muscles, when activated, develop tension, which
in turn generates forces at, and moments across, the synovial joints.
Figure 1.2 The seven
components that form
the functional basis for
the way in which we
walk. This top-down
approach constitutes a
cause-and-effect model.
4 Synovial joint
Movement 6
Rigid link segment 5
External forces 7
2 Peripheral nervous system
1 Central nervous system
Muscles 3