proposal biomechanics gait analysis lab - Biomedical Engineering ...

PROPOSAL
BIOMECHANICS GAIT ANALYSIS LAB
BY:
Kimberly Carr, Omar Chawiche, Angela Ensor
CLIENT CONTACT:
Dr. John D. Enderle
University of Connecticut
Biomedical Engineering Department
Program Director & Professor for Biomedical Engineering
Bronwell Building, Room 217C
260 Glenbrook Road
Storrs, Connecticut 06269-2247
Voice: (860) 486-5521
FAX: (860) 486-2500
Email: jenderle@bme.uconn.edu
Website: www.eng2.uconn.edu/~jenderle
BME Program Homepage: www.bme.uconn.edu
EMB Magazine Homepage: EMB-Magazine.bme.uconn.edu
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TABLE OF CONTENTS
Section Page Number
1. Introduction 1 – 6
1.1 Background 1
1.2 Project Purpose 1
1.3 Previous Work Done by Others 1 - 4
1.3.1 Products 5
1.3.2 Patent Search Results 6
2. Project Description 7 – 14
2.1 Objective 8 – 9
2.2 Methods 9 – 13
3. Budget 14
4. Conclusion 15 - 16

1. Introduction
1.1 Background
Dr. John D. Enderle is the Editor-in-Chief of the EMB Magazine,
Biomedical Engineering Book Series Editor for Morgan and
Claypool Publishers, and the Program Director & Professor for
Biomedical Engineering at the University of Connecticut. Dr.
Enderle has been looking to improve the gait analysis lab for
the undergraduate Biomedical Engineering program’s Biomechanics
laboratory. Currently, the biomechanics gait analysis lab
essentially consists of the students participating in the
process of acquiring data through software applications in the
forward motion only, which limits the students to only obtain or
calculate measurements of distance, acceleration, speed, angles,
and joint moments using the assumption that the ground reaction
forces exerted is simply the subject’s weight. The missing
component to the gait analysis is a true-life measure of ground
reaction forces exerted on the foot strike, which are applied in
multiple directions.
1.2 Project Purpose
Dr. Enderle has requested an expansion of the gait analysis lab
by utilizing a force measurement system. This improvement will
afford students the opportunity to obtain an accurate
measurement of the affects of motion in more than one direction.
The new system will record and provide data on the affects of
foot strike. The addition of a force measurement system will
add value to the lab and the Biomedical Engineering program by
allowing for a more “real world” biomechanics laboratory
experience. Many gait analysis laboratories across the world
have a force measurement system, along with a motion recording
system.
1.3 Previous Work Done by Others
There are three categories for the collection of gait analysis
data that will be considered in this section; foot pressure,
force plates, and motion systems. The acquired data from these
devices or systems are sent to a computer software program, of
which the type of program is dependent upon the types of gait
analysis devices used and the desired program features, to
synthesize and display the results. Two of the foot pressure
options consist of pressure mats and insoles. The force exerted
on the ground can be collected by force plates and the motion
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systems include electromyography (EMG) and a video motion
system.
Foot Pressure
Tekscan, Inc., located in South Boston, MA, has designed and
manufactured many gait analysis products, including a few models
of pressure insoles and mats. (1c)Pressure insoles can be used,
in a clinical setting, for evaluating patients before and after
surgery, screen for neuropathic disorders such as diabetes, and
measure any length discrepancies in lower limbs, which could
potentially be useful in assessing patients prior to hip
replacement surgery for determining implant specifications. The
insoles work much the same as pressure mats, which consist of
capacitive or force sensitive resistor (FSR) switches placed in
between two pieces of material that is either placed on the
floor as a mat or on the inside or outside of a shoe.
Compression closing switches have two sheets of brass shim rock,
(1b) a thin sheet of brass that has been cold rolled, with a
compressible, non-conductive foam rubber insole, which has holes
containing conductive rubber cylinders, in between the shim
rock. The conductive rubber cylinders make contact with both
sheets of sham rock and close an electric circuit upon
application of pressure. Force sensitive resistor (FSR)
switches have a similar sandwich approach that uses flexible
plastic for the outer layers, with circuits printed on the
inside of the two plastic sheets. In between the plastic
sheets, there is a slender layer of double-sided adhesive, with
holes that allow for areas of contact. Similar to the
compression closing switch, pressure causes the electric circuit
to close, except this device has a resistive electric circuit,
so that when pressure is increased, the resistance decreases.
Force Plate Device
Several models of force plates have been designed and produced
by Bertec Corporation, based in Columbus, OH, Advanced Medical
Technology, Inc., based in Watertown, MA, and Kistler
Instrumente AG, based in Winterthur, Switzerland. Ground
reaction forces can be measured by using a force plate. These
devices include a top plate and a bottom plate or frame, which
are separated by force transducers attached to each corner of
the rectangular or square plates. The entire device is
installed into a platform so that the top plate is flush with
the surface of the platform to prevent changes in a subject’s
gait. As the subject walks along the platform and strikes the
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top plate, the exerted force is transferred to the transducers.
There are two types of force plates called piezoelectric and
strain gauge. The piezoelectric force plate uses quartz
transducers that create an electric charge when force is exerted
on the top plate. The strain gauge force plates have load cells
that measure stress when a force is exerted on the top plate.
In both types, the devices provide vertical and shear forces, as
well as the (1a)“center of pressure” during gait.
Motion Systems
Electromyography (EMG) utilizes electrogoniometers that are
attached to the proximal and distal ends of the limb segments
that are to be evaluated. One manufacturer of electrogoniometer
is Biometrics Ltd., located in the United Kingdom and the United
States, and another is Noraxon, located in the United States and
Germany. These devices are electro-mechanical devices that (1a)
“provide an output voltage proportional to the angular change
between the two attachment surfaces.” This system for motion
analysis makes the assumption that the devices move in sync with
the midline of the segment being measured and therefore, give an
accurate representation of the angular change at the joints of
the segments under consideration. The disadvantage is the
tracking (or in sync motion with the midline) is affected when
the person is not a lean individual, so that any type of bulkyness
will affect the accuracy of the results due to skin or
muscle movement.
ViconPeak is a manufacturer and supplier of motion systems and
is based in the United Kingdom, with two locations in the United
States. Video motion systems, also referred to as
optoelectronic systems or stereophotogrammetry, use one or more
digital video cameras that track markers placed on the body of a
subject. The types of markers used include infrared (IR) lightemitting
diodes (LEDs) and reflective markers. The infrared
(IR) light-emitting diodes (LEDs)require the use of a battery,
circuits, and cables that can be cumbersome to use, but
alleviate the issue of a camera losing sight of the marker. The
reflective markers are much simpler to use and can be just as
effective, even under the restraints of the user maintaining
marker visibility by the camera.
Complete Analysis
The foot pressure devices and the force plate device can be used
in conjunction with the motion systems to offer a more
comprehensive analysis of gait, which is the focus of this gait
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analysis project, and are used clinically. There a numerous
laboratories that utilize gait analysis, some examples include
the Derby Gait and Movement Laboratory (www.gait.com), the Hugh
Williamson Gait Analysis Laboratory
(www.rch.org.au/gait/index.cfm?doc_id=1595) as part of the Royal
Children’s Hospital in Melbourne, Australia, and the Shriner’s
Hospital for Children. One company that provides entire gait
analysis systems is Ariel Dynamics, at www.arielnet.com.
1.3.1 Products
Tekscan, Inc. Products for Foot Pressure Devices:
F-Scan ® System
Bipedal In-Shoe Plantar
Pressure/Force Measurement
www.tekscan.com
Walkway TM System
Floor Mat-based Pressure/Force Measurement
www.tekscan.com
Bertec Corporation Products for Force
Plates:
4060 Force Plate Series
www.bertec.com
Dimensions in mm(342A X 552B X 29C X 24D)
4060-08 model is made of solid aluminum
4060-NC Force Plate Series
Dimensions in mm(342A X 552B X 29C X 24D)
Non-conductive and made of resin
impregnated wood.
www.bertec.com
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NorAngle Electrogoniometer System (for
Electromyography EMG)
www.noraxon.com
ViconPeak High Speed Video Camera
Model HSC-200 PM
www.vicon.com
1.3.2 Patent Search Results
Searching for United States patents prior to undertaking an
engineering project or design is obligatory. A patent restricts
the use of any part of a patented invention, in that, another
company or person cannot make, use, or sell the invention in the
United States for a period of time that depends on the type of
invention. For a design patent, the term period is 14 years
from the grant date of the patent.
A quick search through the US Patent database of patents since
1975 can be done at www.uspto.gov/patft/index.html. Using the
term ‘gait analysis’ in the quick search brought up 110 filed
patents with that term in the text of the patent form. Some of
the patents include:
6,997,882 6-DOF subject-monitoring device and method – February
14, 2006 – Parker, et al.
This patent covers an invention that includes methods and
devices for monitoring and acquiring specific data from a
subject’s movement and physiological measurements, which, in
part, involves the use of an accelerometer.
6,836,744 Portable system for analyzing human gait – December
28, 2004 – Asphahani, et al.
The patent describes an invention for a portable gait analyzer
which uses a type of pressure insole with detachable parts.
5,408,873 Foot force sensor – April 25, 1995 – Schmidt, et al.
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This patent is for another type of pressure insole that consists
of outer layers that are conductive and an inner layer that is
nonconductive.
4,631,676 Computerized video gait and motion analysis system and
method – December 23, 1986 – Pugh; James W.
This patent describes a computerized video gait and motion
analysis system and method that use reflective markers, Sony
Video Motion Analyzers, video recorders and displays, and
computer system for displaying the results obtained from the
data.
2. Project Description
2.1 Objective
The objective of the project is to design a gait analysis lab
for a biomechanics class, so that students may learn about gait
analysis and how the data is analyzed through computer software
applications. In general, gait analysis is used to provide
objective measurements concerning a person’s movement patterns.
The set-up will utilize the LabVIEW® software program to analyze
analog data, and hardware parts such as a force measurement
device to measure the forces and moments generated during
footfall. In addition, National Instruments equipment, which is
already available in the lab, will be used for the purpose of
image acquisition and a digital camera to record the gait cycle.
To record the gait cycle using the digital camera, external
markers are placed laterally on the hip, knee, and ankle of the
right or left leg depending on the camera set up, which reflect
light to the camera and allow the segment of motion to be
monitored. To properly set up the force measurement device in
the biomechanics laboratory, it must be placed so that the
person can complete one full gait cycle and step on the
measuring device, with the digital camera placed so that it will
receive the reflected light from the markers. The camera should
be connected to the National Instrument PXI-1031 which contains
the National Instrument 1411 series, consisting of PCI and PXI
plug-in image acquisition cards that receive analog signals from
a standard color or monochrome camera. The BNC-2100 series
connector block is added to the set-up for ease of connectivity
and control of the analog input, analog output, and digital I/O.
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In the laboratory, the students will connect the digital
recorder camera to the National Instrument PXI-1031 device,
followed by connection to the BNC-2100 series connector block,
to regulate the process, and connect BNC-2100 to the computer.
Additionally, students may be required to build a portion of the
LabVIEW® software program to analyze the data. Students will
then place the markers on the different segments of the
subject’s leg. The subject will walk towards the force
measurement device, stepping on the device during the cycle,
while the digital camera records the action. Throughout the
entire process, the National Instrument devices and LabVIEW®
program transform the digital data into analog data, which can
be used to determine distance, speed, acceleration, angles, and
forces acting on the body. The results will provide information
that characterizes an individual’s foot strike pattern.
In the end, the students will learn how the LabVIEW® program
operates, how to set up a laboratory environment, and how the
entire set-up aggregates the information gathered to give
meaningful results.
2.2 Methods
The Clinical Gait Model and Kinematic Data Analysis
The clinical gait model is an algorithm that connects the data
which is collected during the subject’s walking cycles to the
information necessary for scientific analysis. For kinematic
data analysis, three noncolinear reference points or markers are
placed on a subject’s body segment to permit the tracking of the
spatial orientation of that segment through space. From these
reference points, a plane is formed which allows the derivation
of a segmentally fixed coordinate system for the subject. In
order to accurately quantify the subject’s kinematics, markers
have to be referenced to their anatomy and placed either
directly over apparent bony regions on the segment or at
convenient positions along the segment which are visible to the
measurement camera(s) being utilized. For example, markers
placed over the right and left anterior-superior-iliac-spine
(ASIS) and either the right or left posterior-superior-iliacspine
(PSIS), for the pelvis, will allow for the calculation of
an anatomically oriented segmental coordinate system (Figure 1).
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Figure 1. Kinematic markers
used to define pelvis and thigh
coordinate systems. For the
pelvis, PSIS denotes posteriorsuperior-iliac-spine,
H is hip
center, and RASIS and LASIS
denote right and left anteriorsuperior-iliac-spine
markers,
respectively. For the thigh,
TW is thigh wand, K is knee
center, and MK and LK are
medial and lateral knee
(femoral condyle) markers,
respectively.
Kinematic data can also be combined with ground reaction data
such as forces, torque, and their points of application also
referred to as the centers of pressure. Also, the net joint
reactions including joint forces and moments can be computed by
combining the ground reactions with estimates of segment mass
and mass moments of inertia. Consider the following patient
with a mass of 25.2 kg to demonstrate the calculation of the
reactions at the ankle (Figure 2); data for one instant in the
gait cycle are as follows (2a):
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Force Plates
Figure 2. Ankle A and toe T
marker data are combined with
ground reaction force data Fg
and segment mass and mass
moment of inertia estimates to
compute the net joint forces
and moments.
A force plate is a device that measures the ground reaction
forces exerted by a subject as they step on it during gait.
Force plates consist of a top plate, which is mounted level with
the surrounding floor (platform), separated from the bottom
frame by force transducers at each corner; the forces exerted on
the top surface are transmitted through the force transducers.
Force plates allocate the measurement of both the vertical and
shear forces, as well as the center of pressure for the subject
throughout gait. At the moment, there are two types of force
plates commercially available: piezoelectric and strain gauge.
The type of force plate employed does not necessarily make a
significant difference for clinical gait applications.
Piezoelectric force plates (PEFPs) utilize quartz transducers
that produce an electric charge when stressed. These PEFPs do
not require a power supply, but do however, require special
charge amplifiers and low noise coaxial cables in order to
convert the charge to a voltage proportional to the applied
load. Strain gauge force plates (SGFPs) on the other hand, use
strain gauges to measure the stress in specially machined
aluminum transducer bodies referred to as load cells, when a
subject’s load is applied. Unlike the PEFPs, the SGFPs do not
require special cabling or charge amplifiers, but do require
excitation of the strain gauge bridge circuit. Generally, the
PEFPs are more sensitive and have a greater force range than the
SGFPs.
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Pressure Mats
A pressure mat is a quick and easy way of obtaining a plantar
pressure picture of a subject as they walk on it during gait.
Today, there are two types of transducers in use for plantar
measurement: capacitive and force sensitive resistor (FSR). The
capacitor transducers consist of two capacitor plates separated
by a compressible rubber dielectric material. When a pressure
is applied to the transducer, the capacitor plates are pushed
closer together, resulting in a capacitance that is calibrated
in units of pressure. The FSR transducers, on the other hand,
consist of two thin layers of flexible plastic with printed
circuits on the inner surfaces, separated by thin layer of
double-sided adhesive. When a pressure is applied to the
transducer, carbon on one surface contacts a metal pattern on
the other surface, creating a resistive electrical circuit; as
pressure is applied, the resistance drops. Since the
transducers tend to be nonlinear, the precision of these systems
relies on the ability to consistently calibrate them. Commonly,
pneumatic pressure bladder calibration systems are used to
calibrate the transducers, and because the area of the
transducers is known, the applied force may be determined by
summing the force computed from each active sensor for a
particular instance. Pressure mats provide a valuable and quick
way of revealing the areas of high pressure on the plantar
surface of the foot. The following table (Table 1) compares
three different pressure mat systems that are factory calibrated
and provide software that includes color pressure pictures, gait
lines, force and pressure versus time, force and pressure/time
integrals, and masks for detailed analysis of selected areas of
the foot:
Manufacturer
Musgrave
Systems
Novel
Electronics
(EMED)
Tekscan
(F-Mat)
Sensor
Type
Table 1: Pressure Mat Features
Size (mm)
No. of
Sensors
Sensor
Density
(per cm 2 )
FSR 194 x 394 x 38 2,048 2.7 55.6
Capacitive 225 x 445 x 6 2,016 2 70
FSR 320 x 470 x 6 2,128 1.4 120
Sample
Rate (Hz) Calibration
Dynamic
Force
Static
Pressure
Bladder
Static Force
Special
features
Double Plate
System
Available
Podometry
Software
Provided
Real Time
Display
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Gait Mats
A gait mat is a fairly new system that presents both temporal
and spatial gait considerations. Gait mats usually consist of
an array of switches embedded along the entire length of a long
strip of walking surface, like a carpet (Figure 3). As a
subject walks along the mat, the switches close under the feet,
allowing the computer to compute the timing of each switch
closure. The spatial parameters of gait can be determined using
the geometry of the mat. The major advantages of gait mats are
the step length measurements, removal of any gait hindering
attachments, relatively low cost, and portability.
Unfortunately, some disadvantages to using the gait mat are the
temporal resolution due to limitations in the scan rate and the
spatial resolution due to the finite size of the switches. The
following table (Table 2) compares two different gait mat
systems that both provide an extensive database and have
provisions for editing the raw data file:
Manufacturer Type
CIR Systems
(GAITRite)
EQ, Inc.
(Gait Mat)
Portable
(1)
Transportable
(2)
Active Area
(cm)
Table 2: Gait Mat Features
Thickness
(mm)
Switch
Spacing
(mm)
Temporal
Resolution
(msec)
61 x 3.66 4 12.7 11
61 x 4.17 32 15 10
Special Features/
Considerations
Can handle walking aid
patterns, Computes
FAP score (3)
Needs 32 mm thick
runways at each end
for pre & post walk
area (4)
(1) Can be rolled up and carried in a convenient plastic golf case; (2) Folds into four 99 × 41 × 1 cm pieces that fit in a storage case; (3) The
Functional Ambulation Performance (FAP) score is a single numeric representation of a person's gait, based upon temporal and spatial gait data
as well as the person's physical measurements; (4) Manufacturer does not provide runways.
a b
Figure 3. The GAITRite portable gait analysis system. a)
demonstrates the portability of the mat and b) shows a subject
walking along the mat.
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Electrogoniometers
An electrogoniometer is an electro-mechanical device that spans
the desired measured joint from the proximal and distal body
segments (Figure 4). Electrogoniometers supply an output
voltage comparative to the angular change between the two
attachment surfaces. These devices measure the actual angular
change at the specified joint, under the assumption that the
attachment surfaces move along with the midline of the body
segment. There are two main advantages when using
electrogoniometers for gait analysis, they are quite inexpensive
and they are easy to operate. Unfortunately, a major
disadvantage is that skin and muscle movement may cause
inaccurate readings in the subject’s angular change.
Figure 4. A Penny & Giles strain
gauge electrogoniometer applied at
the knee. The strain gauge in the
small spring measures the angle
between the plastic endblocks that
are attached to the leg with
double-sided adhesive tape.
Optoelectronic Systems - Stereophotogrammetry
One or more video cameras can be used in a video system in order
to track the bright markers that are placed on the subject along
specific locations. For a passive marker system, the markers
are usually solid shapes covered with retroreflective tape.
Furthermore, for an active marker system, the markers are
generally infrared (IR) light-emitting diodes (LEDs). Both of
these systems keep track of the horizontal and vertical
coordinates from all of the markers from each camera. For a
three-dimensional (3D) system, the computer software program
calculates the 3D coordinates for each of the specified markers
using the two-dimensional (2D) data obtained from two or more
video cameras. When a single camera is used for gait analysis,
one is assuming that all of the motion is occurring in a single
plane that is perpendicular to the camera axis. This is rarely
the case upon examining a subject’s gait, and as a result, 2D
systems are not recommended for use in gait analysis (2b).
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3. Budget
The cost of building the project is considerable lower compared
to projects that have no components already available and
required to use. This is due to the fact that we already have
much of the equipment that will be used to build the project,
with the exception of the force measuring device. The only
exception may come from the need to use more advance equipment
to obtain accurate data or the current equipment is found to be
incompatible with other components.
The digital camera and tripod that is used for the current
biomechanics lab set-up will be considered for use in the new
lab. Additionally, the National Instrument equipment already in
stock will be used in the new lab and was not previously used.
These devices including the National Instruments PXI-1031 and
the BNC-2100 series connector block.
The LabVIEW® software program is already available on the
computers in the biomechanics lab and in use for other
Biomedical Engineering labs as well, so this project will not
require any additional purchase of software as the customer has
requested the use of this product. A complete system bought
through retailers starts at around $22,000.
Item Retail
Digital Camera(s) $350-$10,000 $0
Camera Tripod(s) $275-$825 $0
Est.
Project
Reflective Ball Markers (set of 30 passive) $300 $105
Computer Software and Computer $2,500-$5,000 $0
Force Measurement Device Components $200-$30,000 $150-$350
Electrical Components $100-$500 $50-$150
National Instruments PXI-1031 $1,000 $0
National Instruments BNC-2100 $295 $0
Miscellaneous $100 $145
Total $5,120-$48,295 $405-$750
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4. Conclusion
The gait analysis lab is important for the Biomechanics class
because the students are able to gain a deeper understanding of
mechanical applications and how gait analysis is used
clinically. Additionally, they will gain further crossfunctional
engineering skills by creating the LabVIEW® software
program necessary to run the lab. The goal of our project is to
build a different gait analysis lab where the students can learn
more about the entire set-up, while keeping the project within a
reasonable budget compared to the cost of a commercially built
lab.
The design of our project is considered to be unique for two
reasons. First it has an added feature that the current lab
does not, which will provide the students with more realistic
results. Missing from the current lab, a force measurement
device will be introduced that will require the students to
determine what forces are applied on the plate and how the plate
operates. The force measurement device will give accurate force
measurements, which were previously assumed. Second, as part of
the new lab, students will be able to gain more knowledge of
gait analysis by learning how to use the software as well as the
hardware aspects of the lab.
Comparing the new lab with the original lab, where students
usually collect the data and use a program to display the
results, in the new lab, creation of the LabVIEW® software
program will provide a more challenging and educational
environment that allows the students to increase their knowledge
of writing programs and applying the program to a real
application. As with the current lab, motion devices will be
used during the lab, so that the students learn how the images
are captured and used to obtain useful results. Finally
students will gain more knowledge about the hardware used
through setting up the lab and connecting all of the devices and
assuring that it works properly.
In the market, the cost of a gait analysis lab with all the
equipment needed starts at around twenty-two thousand United
States dollars, whereas our project will provide a lab that
should fall under 5 percent of market cost. Our most costly
expense is expected to come from the plate measurement device,
which will also be produced considerably less than market value.
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Overall, this project will provide the added components that
have been delayed due to the time constraints of Dr. Enderle’s
growing department. The final results will provide all of the
elements required to make a more robust and successful
educational experience for the students.
References and Bibliography for Section 1.3:
(1a) Instrumented Gait Analysis Systems by Ernest L. Bontrager,
MS.
www.laboratorium.dist.unige.it/~piero/Teaching/Gait/B
NTRAER%20Instrumented%20Gait%20Analysis%20Systems.htm
(1b) www.toolsandsupplies.com/shimstockinfo.htm
(1c) Tekscan, Inc.
www.tekscan.com
www.laboratorium.dist.unige.it/~piero/Teaching/Gait/BONTRAG
ER%20Instrumented%20Gait%20Analysis%20Systems.htm, was used
as a source for the information provided in this section,
with direct quotes noted in the text and with the exception
of reference to (1b).
Mentioned companies can be found at:
www.teckscan.com
www.bertec.com
www.amti.biz
www.kistler.com
www.biometricsltd.com
www.vicon.com
References and Bibliography for Section 2.2:
(2a) Enderle, J. D.(2000). Introduction to Biomedical
Engineering. San Diego, CA. P. 451-457.
(2b) Instrumented Gait Analysis Systems by Ernest L. Bontrager,
MS.
www.laboratorium.dist.unige.it/~piero/Teaching/Gait/BO
NTRAGER%20Instrumented%20Gait%20Analysis%20Systems.htm
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