Specialized Transfemoral External Prosthetic Support Team Final Report

2016/2017 Final Project Report 1 STEPS
LETOURNEAU UNIVERSITY
SCHOOL OF ENGINEERING AND ENGINEERING TECHNOLOGY
ENGR 4813 / ENGR 4823 SENIOR DESIGN
TEAM FINAL
REPORT
2016 / 2017
Project Title: Specialized Transfemoral External
Prosthetic Support (STEPS)
Faculty Director: Dr. Kotaro Sasaki
Student Name : Sonia Sosa Saenz
Andrew Adamo
Aaron Conrad
Dolores Henson
Joshua Kucera
Jessanne Lichtenberg
Raul Saldana
Garret Senti
Anna Steege
Joseph Wilcox
Date Submitted: April 28, 2017
REPORT TITLE: ASSISTIVE DEVICE
FOR TRANSFEMORAL
AMPUTEE

LETOURNEAU UNIVERSITY
SCHOOL OF ENGINEERING AND ENGINEERING TECHNLOGY
E N G R 4 8 1 3 / E N G R 4 8 2 3 S E N I O R
D E S I G N
L I M I T AT I O N S O F U S E
LeTourneau University, the School of Engineering and Engineering
Technology, and faculty of LeTourneau University, do not accept any
responsibility for the truth, accuracy or completeness of material contained
within or associated with this report.
Persons using all or any part of this material do so at their own risk, and
not at the risk of LeTourneau University, its School of Engineering and
Engineering Technology, or the faculty of LeTourneau University.
This document reports an educational exercise and has no purpose or
validity beyond this exercise. The sole purpose of the course pair
ENGR4813 and ENGR 4823 is to contribute to the overall education within
the student’s chosen degree program. This document, associated hardware,
software, drawings and other material set out in the associated appendices
should not be used for any other purpose: if they are so used, it is entirely at
the risk of the user.
Dr. Matthew Green
Interim Dean
School of Engineering and Engineering Technology

CERTIFICATION
I certify that the ideas, design and experimental work, results, analyses and
conclusions set out in this report are entirely my own effort, except where otherwise
indicated and acknowledged.
I further certify that the work is original and has not previously been submitted for
assessment in any other course or institution, except where specifically stated.
Your Full Name
Signature
Date

SUMMARY
The STEPS (Specialized Transfemoral External Prosthetic Support) team aimed
to design, build, and test an assistive device for a transfemoral amputee with a
mechanical prosthetic knee. The reason behind the project was the limited
provision of mechanical prosthetic knees in low resource environments and the
high cost of active prosthetic knees. The goal was to develop a device that
stabilized the knee joint during stance phase and improve gait performance,
especially on uneven ground.
There were two main phases and thus sub teams for the project: design and
testing. The design team fabricated two versions of a device that engages during
heel strike to provide resistance to the knee during stance phase to prevent
buckling. An alpha prototype was created in the fall, which featured a ratchet
design that utilized a foot spring, tension cable, and gear and pawl. Meanwhile, the
testing team developed a testing protocol to determine the efficacy of the device.
In the spring, a beta prototype was created with an ankle switch and linear pawl
system.
To accurately test the device, a transfemoral amputee (TFA) subject would be
needed. Instead of using actual TFAs, the testing experiments would be safer and
more efficient if individuals without mobility impairment simulated motor tasks
affected by the impairment. Therefore, a transfemoral prosthetic gait (TPG)
simulator was created. Using the TPG simulator, a subject without amputation
could simulate TFA gait and wear the developed device. The subject not wearing
the TPG simulator becomes the datum for comparison.
After the beta prototype was completed, several biomechanical variables were
measured and analyzed to validate the efficacy of the device. These included the
kinematic joint angles of the ankle, knee, and hip; the muscle activity of the tensor
fascia latae, gluteus medius, semitendinosus, and rectus femoris; as well as the
steady-state oxygen consumption. All of these were analyzed for three different
conditions: control, TPG simulator, and TPG simulator with the device.
The results from testing demonstrated that the created device successfully
improved aspects of the subjects’ gait as measured by the kinematics, ground
reaction forces, and muscle activation patterns. The simulated TPG using the
STEPS device resembled that of the healthy subjects, indicating that the STEPS
device has the potential to improve the gait performance of TFAs. Additionally, the
STEPS device did not significantly increase the energy expenditure of the
simulated TFG.
In conclusion, the first year of the STEPS senior design project was able to develop
a functioning device that improved the gait of a simulated TFA.

CONTENTS
CERTIFICATION..........................................................................................................................3
SUMMARY .....................................................................................................................................4
CONTENTS.....................................................................................................................................5
LIST OF FIGURES ........................................................................................................................7
LIST OF TABLES ..........................................................................................................................9
NOMENCLATURE......................................................................................................................10
1. PROJECT OVERVIEW ..........................................................................................................11
1.1 INTRODUCTION...............................................................................................................11
1.2 PROJECT GOAL................................................................................................................11
1.3 PROJECT OBJECTIVES .....................................................................................................11
1.4 DELIVERABLES...............................................................................................................12
2. PROJECT BACKGROUND....................................................................................................14
2.1 INTRODUCTION...............................................................................................................14
2.2 REVIEW OF PREVIOUS SENIOR DESIGN PROJECTS.............................................................14
2.3 LITERATURE REVIEW......................................................................................................14
2.4 REVIEW OF STANDARDS AND SPECIFICATIONS ................................................................18
2.5 SUMMARY OF FINDINGS ..................................................................................................19
3. CLARIFICATION OF PROJECT..........................................................................................20
3.1 GENERAL OVERVIEW ......................................................................................................20
3.2 KEY PROJECT STAKEHOLDERS .......................................................................................20
3.3 REQUIREMENTS AND CONSTRAINTS ................................................................................21
3.4 SPECIFICATIONS AND TARGET VALUES ...........................................................................22
4. ASSESSMENT OF CONSEQUENTIAL EFFECTS.............................................................23
4.1 SUSTAINABILITY ASSESSMENT........................................................................................23
4.2 PROFESSIONAL AND ETHICAL CONSIDERATIONS.............................................................25
5. INDIVIDUAL ROLES .............................................................................................................28
5.1 RELATIONSHIP OF INDIVIDUAL ROLES TO OVERALL PROJECT .......................................28
5.2 INDIVIDUAL WORK DESCRIPTIONS.................................................................................29
6. OVERALL PROJECT DEVELOPMENT .............................................................................34
6.1 TRANSFEMORAL PROSTHETIC GAIT SIMULATOR ............................................................34
6.1.1 Purpose .....................................................................................................................34
6.1.2 Validation..................................................................................................................35
6.2 DESIGN & EMBODIMENT ................................................................................................35
6.2.1 Alpha Prototype........................................................................................................35
6.2.2 Beta Prototype ..........................................................................................................40
6.2.3 Conclusion................................................................................................................43
6.3 TESTING & VALIDATION.................................................................................................44
6.3.1 Overview ...................................................................................................................44
6.3.2 Data Acquisition Methods........................................................................................44
6.3.3 Data Processing........................................................................................................47
6.3.4 Results.......................................................................................................................49
6.3.5 Discussion.................................................................................................................60
6.3.6 Sources of error........................................................................................................64
6.3.7 Conclusion................................................................................................................66
7. CONCLUSION..........................................................................................................................67
7.1 CONCLUSION..................................................................................................................67

7.2 ACHIEVEMENT OF SPECIFICATIONS.................................................................................67
7.3 RECOMMENDATIONS.......................................................................................................68
REFERENCES..............................................................................................................................71
APPENDIX A. GANTT CHARTS ..............................................................................................74
APPENDIX B. TPG SIMULATOR FABRICATION .................................................................I
APPENDIX C. CONFERENCE ABSTRACT........................................................................... IV
APPENDIX D. ALPHA PROTOTYPE ASSEMBLY..............................................................VII
APPENDIX E. ALPHA PROTOTYPE CALCULATIONS..................................................... IX
APPENDIX F. BETA PROTOTYPE PHOTOS ....................................................................... XI
APPENDIX G. BETA PROTOTYPE ASSEMBLY ................................................................XII
APPENDIX H. BETA PROTOTYPE CALCULATIONS ......................................................XV
APPENDIX I. BILL OF MATERIALS ............................................................................... XVIII
APPENDIX J. SOLIDWORKS DRAWINGS ........................................................................ XIX
APPENDIX K. SUBJECT GAIT PARAMETERS............................................................XXXII
APPENDIX L. MARKER SETS ....................................................................................... XXXIII
APPENDIX M. EMG ELECTRODE LOCATIONS.....................................................XXXVIII
APPENDIX N. ENERGY EXPENDITURE PROCEDURE...................................................XL
APPENDIX O. JOINT ANGLE GRAPHS..............................................................................XLI
APPENDIX P. EMG GRAPHS ..........................................................................................LXVIII
APPENDIX Q. GRF GRAPHS......................................................................................... LXXVII
APPENDIX R. OXYGEN CONSUMPTION ................................................................... XCVIII
APPENDIX S. EXPENDITURES......................................................................................... XCIX

LIST OF FIGURES
Figure 5-1. STEPS Team Organization..............................................................28
Figure 6-1: Transfemoral Prosthetic Gait Simulator............................................34
Figure 6-2. Model of Clutch Plate Concept in Solidworks...................................35
Figure 6-3. Model of Ratchet Concept in Solidworks..........................................36
Figure 6-4. Model of Internal Ratchet Concept...................................................36
Figure 6-5. Alpha Prototype: Gear and Ratcheting Pawl ....................................38
Figure 6-6. Alpha Prototype: Foot Spring and Tension Cable ............................38
Figure 6-7. Assembled Alpha Prototype with TPG Simulator .............................39
Figure 6-8. Assembled Beta on TPG Simulator..................................................41
Figure 6-9. Anti-Rotation Switch System............................................................42
Figure 6-10. Beta Prototype: Anti-Rotation Switch System with the Dowels(left),
Pylon Insert (middle), and Upper Endcap (Right). ..............................................42
Figure 6-11. Beta Prototype: Locking Mechanism..............................................43
Figure 6-12. Hip, Knee and Ankle Joint Angles for Right/Affected and Left/Intact.
Gait cycle corresponded to Right/Affected Limb Heel Strike to Heel Strike.
Additional Joint Angle graphs are in Appendix O. ..............................................49
Figure 6-13. Joint Angles of Hip, Knee and Ankle. Gait cycle corresponded to
Left/Intact Limb Heel Strike to Heel Strike. Additional Joint Angle graphs are in
Appendix O........................................................................................................51
Figure 6-14. Right/Affected limb ground reaction forces in the Y-direction
(Superior/Inferior). See Appendix Q for additional GRF graphs..........................53
Figure 6-15. Left/Intact limb ground reaction forces in the Y-direction
(Superior/Inferior). See Appendix Q for additional GRF graphs..........................53
Figure 6-16. Right/Affected limb ground reaction forces in the X-direction
(Anterior/Posterior). See Appendix Q for additional GRF graphs........................55
Figure 6-17. Left/Intact limb ground reaction forces in the X-direction
(Anterior/Posterior). See Appendix Q for additional GRF graphs........................55
Figure 6-18. Right/Affected limb ground reaction forces in the Z-direction
(Medial/Lateral). See Appendix Q for additional GRF graphs.............................57
Figure 6-19. Left/Intact limb ground reaction forces in the Z-direction
(Medial/Lateral). See Appendix Q for additional GRF graphs.............................57

Figure 6-20. Normalized muscle activation patterns of the right/affected leg. See
Appendix P for additional EMG graphs. .............................................................59
Figure 6-21. Steady State Oxygen Consumption with 95% Confidence Interval at
1.3 mph and 5° incline. See Appendix R for additional data...............................60
Figure 6-22. Weight Bearing Comparison ..........................................................62

LIST OF TABLES
Table 3-1. Key Project Stakeholders ............................................................20
Table 3-2. Requirements & Constraints........................................................21
Table 3-3. Specifications..............................................................................22
Table 6-1. Decision Matrix............................................................................37
Table 6-2: Subject Demographics ................................................................44

NOMENCLATURE
Abbreviation Explanation
CAD Computer-Aided Design
CI Confidence Interval
COM Center of Mass
EMG Electromyography
GRF Ground Reaction Forces
KAFO Knee-Ankle-Foot Orthosis
LEGS LeTourneau Engineering Global Solutions (LEGS)
SCKAFO Stance Control Knee-Ankle-Foot Orthosis
SMART Specialized Mobilization and Rehabilitation Team
STEPS Specialized Transfemoral External Prosthetic Support
TF Transfemoral
TFA Transfemoral Amputee
TPG Transfemoral Prosthetic Gait
TT Transtibial
VO2 Oxygen consumption, oxygen uptake, aerobic capacity
VO2max Maximal oxygen consumption
WHO World Health Organization

1. PROJECT OVERVIEW
1.1 INTRODUCTION
Upon amputation, an amputee is prescribed a prosthetic limb. A transfemoral
prosthesis consists of a metal frame that interfaces between the remaining limb
and the mechanical support system. This system is composed of a knee joint, an
extension (pylon) that replaces the length of the lost limb, and a prosthetic foot [1].
A transfemoral prosthetic with a mechanical knee joint allows the user to walk with
functional gait on smooth surfaces, but fails to provide stabilization during stair
climbing and uneven surfaces due to the passive knee [2]. Limited performance is
observed since mechanical knees must lock at full extension during stance phase
of gait to allow the user to bear weight on the device [3]. The full extension
mechanism can be harder to activate while this type of prosthetic knee is in use on
rough terrain. Lastly, walking with a transfemoral prosthesis has a greater energy
demand as compared to healthy individuals [4].
The lack of power generation at the knee causes a transfemoral amputee (TFA) to
adopt a step-to-step approach for stair climbing. This nonreciprocal method allows
the intact limb to do most of the work, and is inefficient and time consuming [2].
Furthermore, mechanical knees are predominantly used in low resource settings
due to the more affordable cost [5] . Consequently, a need arises to tailor passive
prosthetic knees to improve gait for TFAs by providing stabilization at the knee,
especially for stairways or uneven surfaces.
1.2 PROJECT GOAL
The Specialized Transfemoral External Prosthetic Support (STEPS) team aimed
to design and test an external prosthetic support device for TFAs that met the
requirements of low cost, lightweight, low maintenance, compatible with prosthetic,
effective in stabilizing the knee joint during stance phase, and improvement of the
quality of daily activities, including stair climbing. The device will assist the gait
of TFAs on level ground, stair climbing and inclines by providing knee joint
stabilization during stance phase.
1.3 PROJECT OBJECTIVES
1.3.1 Research
In order to optimize the assistive device, the team conducted a literature search
on the common problems and characteristics of TFA gait. In particular, research
focused on the effects of a transfemoral amputation and existing devices
that stabilize the stance phase of gait. The findings were outlined in a literature
review (see section 2.3.).
1.3.2 Transfemoral Gait Simulation
To test our device without a prosthetic user, a healthy subject imitated the gait of
a TFA using a TPG simulator. The subjects’ dominant leg was immobilized at
110° knee flexion with a leg brace. A prosthetic knee was attached to a metal

frame and connected to an adjustable pylon and a prosthetic foot. This
combination allowed the team to test the STEPS assistive device with
simulated TFA gait. By using the TPG Simulator as a representation of TFA gait,
the team ensured the safety of all subjects during testing and created a baseline
of comparison between healthy gait, simulated TF gait, and simulated TF gait with
the assistance of the STEPS Device.
1.3.3 Alpha Prototype Device Fabrication
Using insights gained from a transfemoral gait simulation literature search, the
STEPS team fabricated an assistive device to optimize support during the stance
phase and to improve gait stability on uneven terrain. The device will
accomplish these requirements by preventing knee flexion during the weight-
bearing stage of the stance phase. After locking, the device will only allow knee
extension. The timing and duration of this phase will be strategically determined
by analysis of restricted ankle/knee trials and through the literature review.
1.3.4 Testing and Analyzing with Device
The STEPS assistive device will be evaluated based on the energy consumption
required for use and kinematic data. The energy consumption will be measured
with a COSMED FitMate PRO, an oxygen uptake monitor [Cosmed, Rome, Italy].
The kinematic data will be collected with a motion capture system (VICON Motion
Systems Ltd., Oxford, UK) which utilizes seven cameras, a force plate (FP4060-
07-1000, Bertec, Columbus, OH), analysis software (Nexus Ver. 2.5, VICON,
Oxford, UK), and musculoskeletal simulation software (OpenSim Ver. 3.3, SimTK,
Stanford, CA).
1.3.5 Beta Prototype Device Fabrication
After reviewing the performance with the alpha prototype, the team will analyze
potential improvements and design a beta prototype that addresses any
discovered issues.
1.4 DELIVERABLES
1.4.1 Transfemoral Prosthetic Gait Simulator
TFA gait will be simulated using a fabricated TPG simulator. Analysis will be
performed to validate the simulator as a reliable representation of TFA
gait. Oxygen intake during testing will be measured using a COSMED FitMate to
evaluate the necessary energy required.
1.4.2 Alpha Prototype
Based on relevant literature, gait simulations, and similar devices, a preliminary
prototype will be developed during the first semester of the project. After testing
and analysis, the effectiveness will be evaluated and potential methods of
improvement will be considered for the Beta prototype.

1.4.3 Protocol Tests
The testing team will perform preliminary tests to establish a protocol for device
testing. Various conditions and variables will be tested to define the best method
of biomechanical analysis.
1.4.4 Beta Prototype
Using data from the Alpha prototype testing, the Beta prototype will be fabricated,
addressing major issues from the previous design. This will be the final prototype
used for testing during this project term.
1.4.5 Beta Prototype Tests
With the completed second prototype, the team will test the product's
effectiveness in increasing the ability of a TFA to complete different gait motions
and decreasing the oxygen consumption.
1.4.6 Documentation and Presentations
Over the course of this one-year project, the team will provide the proper
documentation necessary to effectively communicate their work and pass their
findings on to future project teams. Through the development of the device, an
online storage sharing drive will be used for team collaboration. A final report,
presentation, and poster will be completed to demonstrate the end results of the
project.

2. PROJECT BACKGROUND
2.1 INTRODUCTION
Background research is required to successfully accomplish the goals of the
STEPS team. This will take place in the form of journal article reviews, patent
searches, and investigation of similar devices.
2.2 REVIEW OF PREVIOUS SENIOR DESIGN
PROJECTS
The STEPS team is the first generation of this senior design project. However,
the project has similar goals of previous senior design teams such as SMART and
LEGS. The SMART project analyzed the effects of using AmTryke tricycles as
physical therapy for children with neuromuscular impediments manifested in
uncoordinated movements. The LEGS project focused on the design and testing
of a low cost prosthetic for TFAs in limited resourced countries. While the concepts
of these two projects are different from STEPS, the design opportunities share
similarities. The LEGS and STEPS projects are especially similar with the shared
target of limited resourced settings.
2.3 LITERATURE REVIEW
In the United States 30,000 transfemoral (TF) amputations are performed each
year [6]. From a 2005 study on the prevalence of limb loss in the United States,
40% of the total limb losses were major lower limb losses. The projected population
in the United states living with a lost limb by 2020 is 2.2 million people, and the
estimated number of people living with a major lower limb loss by 2020 is 880,000
people [7].
These statistics are higher for low-income countries, where 80% of the disabled
population lives [8]. Recent estimates by the World Health Organization (WHO)
predicted 30 million people were in need of prosthetics [8].
In this literature review, the following topics will be covered: an analysis on the
provision of TF prosthetics, especially in low resource environments; an emphasis
on the consequences of TF amputation versus transtibial (TT) amputation, a
review of characteristics of TFA gait, an overview of a similar stance control device,
and an assessment on quality of life of a TFA.
2.3.1 Provision of TF prosthetics
The WHO also reported the import of prosthetics and orthotics from high-income
countries failed to meet the actual needs of people with disabilities in low-income
countries. This issue is mostly due to maintenance and repair issues because
spare parts are hard to find [8]. Another problem is imported devices may not be
designed for rural environments, decreasing the lifespan of the product [1]. For
these reasons, low cost prosthetics are mostly mechanical and passive because

prosthetics with microcontrollers tend to be more expensive and might be
unsuitable for the environment [5].
Even in high-income countries such as the United States, the opportunity to get a
powered prosthetic is scarce since government reimbursements only account for
40-50% of the prosthetic service and device cost [9]. For $5,000 - $7,000, a patient
with a below-the-knee amputation can have a prosthesis that fulfills the user’s
basic needs such as standing or walking on level ground. For $15,000, a TFA can
obtain a prosthesis containing polycentric mechanical knees, swing phase control,
stance control, and mechanical or hydraulics system [9]. From these estimations,
it can be concluded the cost of the prosthesis increases as the level of amputation
becomes more proximal to the trunk.
Active vs. Passive Knees
Two main types of prosthetic knees exist, passive and active. Active knees provide
power generation via a motor or microprocessor unit, whereas passive knees do
not. Due to the high cost of prosthetics with advanced knee joint technologies,
most TFAs rely on passive, or mechanical, devices [10]. However, these knees
are limited in their performance because mechanical knees must lock at full
extension during the stance phase of gait to allow the user to bear their weight on
the device [3]. For example, a weight-activated braking knee provides greater
stability during the weight-bearing phase of gait, but at the trade-off of an increased
difficulty to flex the knee when transitioning from stance phase to swing phase [10].
The lack of power generation at the knee restricts the ability of the mechanical
knee to restore proper gait for the user.
A passive knee can also inhibit the variety of ground surfaces a subject can easily
travers. In a study where subjects were tested with a passive and active prosthetic
walking on uneven ground, researchers found the subjects with power at the knee
had increased symmetry in their gait [3]. If a person is walking on uneven ground
with a prosthetic knee, the gait is more variable on this surface because of the
difficulty for the user to predict the best way to load the foot onto the surface [3].
This could result in the user adopting cautious gait patterns defined by reduced
speed, stride length and widening of base support [3]. These uneven surfaces can
increase the chances of falling [3]. Therefore, while the lower cost of a passive
knee appeals to TFAs, the lack of power generation at the knee ultimately limits
the functional gait possible.
2.3.2 Transfemoral vs. Transtibial Amputation
When comparing TF and TT amputations, TF amputation consistently causes a
greater difficulty in walking than with TT amputations. In a study that compared TF
and TT amputations by measuring energy consumption during gait, a distinct
difference was found between the two groups. At a self-selected speed, the
subjects with TF amputations walked more slowly and with a higher energy
consumption than the subjects with TT amputations [11]. Another study evaluated
the biomechanical factors relating to the intact limb needing to compensate for an
amputee's asymmetrical gait. The compared subjects were individuals without
impairment and those who had TF and TT amputations. The results of the testing
showed significantly greater ankle, knee, and hip moments of the intact limb with
TF subjects when compared to subjects with TT amputations [12].

Another study found an increase in velocity caused TF amputees to reduce the
asymmetry of loading time during gait, whereas TT amputees did not create this
compensation [13]. The intact limb is responsible for this compensation, so a
greater loading was seen on this limb in TF amputees. This excessive loading can
lead to degeneration of the intact limb over time. The authors also found that
subjects spent more time bearing weight on the intact limb than the affected limb.
Their hypothesis being, the subjects had discomfort or pain in the affected limb,
and they did not "trust" this limb as much as the intact limb [13]. This is an area the
STEPS team would like to improve by adding knee stabilization during gait that
could increase a user's confidence in the prosthesis' ability to hold their weight
safely.
2.3.3 Transfemoral Amputee Gait
The gait of a TFA is typically different than a non-amputee due to the lack of
musculature in the lower limbs. This is evidenced through analyzing the kinetics,
kinematics, energy consumption, and muscle activity of TFAs.
Kinetics & Kinematics
A study where muscle activity patterns were compared between TFAs and healthy
subjects, determined that TFAs tend to increase the stance phase duration of the
intact limb and decrease the prosthetic swing phase duration [14]. TFAs find more
difficult to perform hip abduction, which makes foot clearance difficult [14].
Researchers also observed electromyography (EMG) and kinematic data highly
variable between amputee subjects, which can be due to the differences in each
amputee’s walking pattern and residual muscle length [14].
A study comparing a microprocessor knee to a passive knee highlighted the
weaknesses of a purely mechanical knee [15]. This study showed that the C-Leg
(Ottobock, Germany) allows TFAs to walk faster with a symmetric stride, while the
Mauch SNS knee (Össur, Iceland) caused slower gait and different stride lengths
between legs. The peak swing phase knee flexion angle tended to be lower in the
microprocessor knee and about ten degrees larger in the Mauch Knee with values
of (55.2° ± 6.5° vs 64.41° ± 5.8°, respectively; p =0.005) [15]. Another discovery
emphasized in this text is that mechanical knees tend to be optimal at some
speeds, but not all speeds. Since the knee must be locked while walking, it was
difficult to produce a smooth gait and caused a higher metabolic cost for the TFAs.
Joint forces in the unaffected knee were much higher in TFAs than the individuals
without impairment due to the compensation forces acting on the knee within
activity. These compensation forces caused gait asymmetries which lead to
fatigue, injuries, and degenerative arthritis. Biomechanical analysis determined
that the main cause of gait asymmetry experienced by TFAs was the increased
hip extensor activity of the affected limb in an effort to assist in knee stabilization
[15].
Energy Consumption
Researchers concluded that walking with a TF prosthesis requires higher energy
expenditure than non-amputees no matter how fast the gait [4]. As a result, the
activity level of TFAs and the types of activities they can participate in is limited [4].
This is particularly seen in the case of a walking surface that is tilted sideways to
simulate an outdoor environment. In this scenario, TFAs compensated by adopting
a more energy consuming gait pattern [4]. In one study where the subjects reported

themselves being generally physically fit, TFAs used a larger percentage of their
maximal aerobic capacity than healthy participants to perform normal activities of
daily life [4]. While many factors could be attributed to the increase in energy
consumption used by TFAs, one theory is that heavier prosthetic devices cause
an increase in energy expenditure [16]. However, some researchers hypothesize
that improving the swing phase of gait could be more influential in decreasing
energy expenditure than decreasing the weight of the prosthesis [16].
Muscle Activity
On a physical note, the amputee loses major muscles such as the vasti,
hamstrings, gastrocnemius and soleus. An individual with a TF amputation loses
two major joints, the knee and ankle [17]. A prescribed prosthesis helps in
ambulation, but as discussed previously, the capacity to generate power at the
joints is lost due to the lack of major muscles. From a study where vastus medialis,
vastus lateralis, rectus femoris, biceps femoris, semitendinosus, gluteus maximus,
soleus, tibialis anterior, and gastrocnemius muscles were studied during stair
climbing, it was determined during stair ascent, the muscle activity of the un-
affected leg is greater than that of a healthy individual [18]. During stair descent,
the muscle activity of the un-affected leg was 68% greater than a healthy individual
[18].
A study pertaining to male TFAs with osseointegrated fixations compared to
nondisabled male volunteers studied the EMG cycles of both types of subject. The
data from this study showed that TFAs produced cyclical muscle patterns
pertaining to 5 specific muscles: adductor magnus, biceps femoris, gluteus
maximus, gluteus medius, and rectus femoris. For osseointegrated fixations, the
rectus femoris, biceps femoris, and adductor magnus all lost connection to the
patella. The two femoris muscles become unilateral as well. Due to the lack of
anchoring at the knee, a force could not be exerted to initiate the swing phase in
the same way an unimpaired subject would [19]. The surface EMG results
revealed that the TFAs had no initial adductor magnus impulse to propel into swing
like the uninhibited subject. Another difference in the groups was observed in the
late stance phase where the TFAs had high adductor magnus and gluteus medius
activity which causes the hip hiking motion [19]. A cyclical muscle activation
pattern in the TFAs was not expected due to the dramatic change in musculature
from amputation. However, this study showed that TFAs to have a cyclical gait
which alludes to the possibility of attaining a gait pattern similar to a healthy
individual.
2.3.4 Comparable Solutions: KAFOs
Knee-ankle-foot-orthoses (KAFOs) are braces prescribed to individuals with lower
limb instability. These assistive devices provide stability during walking by locking
the knee joint in a fully extended position during the gait cycle [20]. However, this
can require elevated energy consumption, leading to premature exhaustion during
gait, and causing limited mobility, pain, and decreased range of motion [20]. To aid
this issue, stance control KAFOs (SCKAFOs) have been developed to prevent
knee flexion during stance phase and permit free knee motion during the swing
phase of gait [20]. In studies performed to analyze the effectiveness of SCKAFOs
in improving gait kinematics of the users, it was found that the devices do
overcome the limitations of traditional KAFOs [20], [21]. Specifically, the devices
support the knee joint during stance phase by maintaining extension and allowing
free knee flexion during swing phase [20], [21]. Therefore, the new designs have

improved the kinematics for KAFO users. In another study, most subjects showed
increased gait velocity when using the SCKAFO versus the traditional KAFO [21].
2.3.5 Quality of life
Limb loss not only affects individuals physically, but also alters social interaction
and independence. While mechanical knees may help to regain ambulation after
amputation, stair climbing can be a challenge to TFAs. Amputees have a lesser
chance of gaining functional household or community mobility as the level of
amputation becomes more proximal to the trunk [22]. A study performed in 2010
evaluating several factors affecting quality of life in lower limb amputees revealed
that 52% of the people interviewed were unemployed when the study was
conducted, while 80% of those unemployed reported being employed prior to
amputation [23]. A majority of the interviewees (82%) stated that the loss of their
jobs was directly related with the amputation [23]. From these studies one can
conclude amputation has a direct impact on the individual’s functionality, having
repercussions on employability and consequently the family’s income and lifestyle.
The later study proposed that an effective use of prostheses that allows amputees
to reintegrate into the workforce may result in an improved quality of life [23]. In
addition, people with non-vascular unilateral TF amputations cannot walk quickly
or walk in woods or fields, resulting in an impaired quality of life in general [24].
Therefore, the development of a device that addresses the gait impedance of
passive prosthetic knees could help TFAs to regain independency, improve social
interaction, enhance well-being and contribute to family income.
2.3.6 Transfemoral Prosthetic Simulators
During initial prototype evaluations, collecting experimental data from actual
patients would be challenging due to limited access to a laboratory and possible
complications prevalent among patients with mobility impairment [25]. Therefore,
experiments would be conducted more safely and efficiently if individuals without
mobility impairment could perform given simulated motor tasks affected by the
impairment. The use of transfemoral prosthetic gait simulator (TPG simulator) for
testing is a safe and efficient testing method for the project. Other research studies
have used comparable simulators and produced biomechanical results similar to
TFAs. One study using a TPG simulator showed gait kinematics such as joint
angles and stride length parameters consistent with the data obtained from actual
patients [26]. Another study demonstrated the ease of adaptation of healthy
subjects to a TPG simulator [27]. The subjects in the study were all able to walk
unassisted for 30 minutes while wearing a TPG simulator without falling.
2.4 REVIEW OF STANDARDS AND
SPECIFICATIONS
While there are no specific standards and specifications for the team’s novel
device, the team analyzed standards for prosthetics defined in ISO 13405-2:2015,
which specifies a method for describing lower limb prosthetic components. For
knee units, necessary parameters include types of motion and their ranges,
rotation, and adjustability. From this, the team can realize the importance of the
device being adaptable to a variety of knees. For knee unit stance phase control
devices, the type of unit must be clearly defined in terms of the method of activation
of the lock, type/magnitude of resistance, and adjustability. These guidelines aid

the team in designing and building a device that is compatible to existing knees
with detailed specifications.
2.5 SUMMARY OF FINDINGS
From the literature review, STEPS concluded that there is a latent need to improve
TFA knee stabilization, especially over stair and ramp ascent/descent. TFAs lose
fundamental lower limb muscles and joints which affects their daily actions, such
as stair climbing. This impairment may decrease their routine activities due to
higher energy consumption, diminishing their overall quality of life.
While there is an extensive variety of TF prostheses on the market, the cost to
acquire a powered knee is high, making most patients choose a passive
mechanical knee joint. Mechanical knees may help to recover ambulation, but
since they lack the ability to generate power at the knee, the amputee
compensates by implementing more time and energy consuming methods of gait.
These methods often rely more on the intact leg, especially in stair climbing where
TFAs often use a step-to-step approach rather than the typical step-over-step
approach.
The team determined a TPG simulator would be best for test trials this project term
because previously published simulators have proven to be a safe and
biomechanically valid method of testing.
In conclusion, there is a need for a device similar to a stance control KAFO to aide
in the gait of TFAs. Since this device needs to be mounted to the existing
prosthetic, the design should be lightweight and adjustable. With low resource
settings in mind, the device must also be affordable. A device with the described
capabilities has never been developed. Consequently, this is an innovative
opportunity to improve the overall quality of life of TFA patients by allowing a more
natural walking style.

3. CLARIFICATION OF PROJECT
3.1 GENERAL OVERVIEW
The goal of STEPS is to develop a universal, inexpensive, lightweight and low-
maintenance device that is externally mounted to a passive prosthetic
and will successfully stabilize the knee joint throughout stance phase during daily
activities including stair climbing. The device will prevent knee buckling during
stance while unlocking the knee at a certain degree of extension, allowing the user
to complete a gait cycle in a more natural pattern. The data acquired through
testing will determine the overall effectiveness of the device to improve the gait of
the user in different gait patterns such as walking and stair climbing.
3.2 KEY PROJECT STAKEHOLDERS
Table 0-1. Key Project Stakeholders
Stakeholder Name Relationship 1
Description Type2
Dr. Kotaro Sasaki (1) Faculty Sponsor (a)
Medical Personnel (3) Potential Customer (c)
Medical Patients (3) Potential Customer (c)
Low Income Countries (3) Potential Customer (c)
1
Stakeholder relationship classified as (1) Internal = people directly within the project; (2) University = people
within the broader university; (3) External = individuals or organizations outside the university.
2
Stakeholder type is classified as (a), (b), (c) or (d) based on the types outlined above.

3.3 REQUIREMENTS AND CONSTRAINTS
Table 0-2. Requirements & Constraints
Requirement /
Constraint
Description Significance
Compatible to
different mechanical
knees
The device should be easy to install
and compatible with more than one
currently available mechanical knee.
Essential
Lightweight The weight of the device should not
inhibit prosthetic function.
Critical
Low cost An affordable device is necessary for
distribution to a larger population.
Essential
External from
prosthetic
The device should coexist with, and not
suppress the intended function of the
prosthetic.
Essential
Low maintenance for
user
Minimal maintenance and adjustment is
ideal for ease of user.
Critical
Improve user's gait in
stair ambulation
The device should improve the ability of
the user to climb stairs and/or inclines
with reduced effort.
Essential
Long term
sustainability
The device should be able to maintain
proper function and not need
replacement for a long period of time.
Critical

3.4 SPECIFICATIONS AND TARGET VALUES
Table 0-3. Specifications
# Specification Target Value Measurement
Method
1 Kinematic improvement in
gait
10-20 degrees of flexion
during stance phase
Vicon Nexus 3D
motion Capture
system
2 Energy consumption < 12.9 ml/(kg-min)
during level ground
walking
[28]
VO2 Max with
FitMate unit (rate of
oxygen uptake)
3 Muscle activation Decreased Trigno Wireless EMG
sensors
4 Friction ≤ 1N*m Friction Calculations*
5 Max knee torque supported 213 N*m Torque
Calculations*
6 Lightweight < 1lb Laboratory Grade
Scale
7 Long term sustainability > 3 years [29] Fatigue
calculations*
* See Appendix H. Beta Prototype Calculations

4. ASSESSMENT OF CONSEQUENTIAL
EFFECTS
4.1 SUSTAINABILITY ASSESSMENT
Andrew Adamo
The STEPS team is developing a device which maximizes the use of existing
resources to benefit transfemoral amputees in low-income communities located
within developing countries. The materials used within the device are based off
existing prosthetic technology and are a low-cost, low-impact solution to a critical
global need. Using reliable, easily accessible components, the STEPS team is
seeking to develop a device which can be employed beneficially in a variety of
locations even after its original components have failed. As this device is
developed, the benefactors of this project should be included as contributing
stakeholders in order that the sustainability needs of the developing countries
might be best addressed. In many of these third-world areas, the benefactors of
this project will be able to re-engage with peaceful rebuilding through greater
mobility and increased physical abilities.
Aaron Conrad
Most components are steel which is not a precious metal nor an environmental
hazard of itself. The production methods used by the team were primarily water-
jet cutting, which is a notably eco-friendly process. All parts are reusable,
repairable, or recyclable. At time of writing, the materials of the device is not such
a commodity as to cause large-scale dispute or theft.
Dolores Henson
The prosthetic aid developed through this project uses a small amount of stainless
steel which is not wasteful in a large scale consideration. Since this device is
designed to be connected to an already existing prosthetic, it provides a simple
tool for an already existing solution instead of an entirely new product to a user.
Many prosthetics in the developed world have electrical components. The device
designed by this team is purely a mechanical invention which relies on the user in
order to be used. There is no need for external power, only power generated while
walking by the user. This project has the potential to be applied to developing
countries due to the simplicity of the design. The product is projected for use in
areas where prosthetics are purely mechanical have no knee locking mechanisms.
This design could be reiterated by future teams in order to become a marketable
product and distributed to the intended users.
Joshua Kucera
The final product of the STEPS design team is meant to be an efficient and
affordable solution for transfemoral amputees in developing countries. The
materials and machining processes are tailored for this environment in the way
that they are easy to obtain and have a minimal effect on the environment. Parts
that are more likely to wear out are also easily replaced by similar, easy to find
pieces that are not necessarily the originally specified parts. For example, the
tensioning cable could easily be replaced by a simple string if something were to

go wrong and require a simple and quick replacement. Environmental hazards for
this product are primarily limited to the manufacturing processes that are employed
in its construction, and as such make this product a very efficient and sustainable
design.
The result of the STEPS senior design team would have a positive impact on the
usage of resources because it improves an existing prosthesis. The assistive
device create has the potential to optimize an affordable mechanical knee
prosthesis and decrease the need for a more expensive motorized prosthesis. The
thin metal used in the device are low cost are easily manufactured. Because the
device is used directly with human contact, safety was a top priority in the design
and testing of the device. The device created by the STEPS team would benefit
TFA in the United States as well as other countries worldwide. The device is
especially useful in developing countries with inadequate medical provisions. The
sustainability outcomes would not vary by location.
Raul Saldana
One of the goals of our project work is to make our device affordable to third world
countries where trans-femoral amputees are likely unable to acquire advance
prosthetics. We aim to achieve this goal by designing our device to be purely
mechanical. Our device uses thin, easily manufactured parts which reduce waste
production. Although we have designed our device to theoretically last a lifetime,
there are no certainties that it will. There may be some mechanical parts of our
mechanism that will need replacement, which will require more resources and
potentially increase waste production, however little it may be. This may be
reduced in the future given that new more advanced, stronger materials can be
easily produced and manufactured. These materials could potentially allow our
device to last significantly longer. Our device could significantly increase the quality
of life of trans-femoral amputees in not only a third world countries, but trans-
femoral amputees all around the world.
Garret Senti
The device designed by the STEPS senior design team is to supply further stability
and support to existing prosthetic for transfemoral amputees. The assistive device
is a way to optimize a passive prosthetic leg to be just as effective as prostheses
that use a microprocessor. The device has been specialized to be comprised of
only mechanical components as well as being able to attach to prostheses that
utilize a four bar knee joint. Since this device will be used by humans, it is important
to the team to develop the device to be as safe as possible to benefit those in
developing countries and for those who do not have the ability of obtain a
microprocessor prosthetic knee. The device could be developed further to improve
performance by any future team as well as making the device a marketable product
to then be distributed to any potential user.
Sonia Sosa Saenz
This device could have significant implications in the prosthetic world as an aid for
transfemoral amputee gait when using a mechanical (passive) knee. This product
is primarily targeted to low income areas, but the goal is for this device to be used
around the globe. Having in mind the target audience, the device is designed to be

used in all-terrain areas including uneven surfaces, gravel and/or dirt
environments. Most of the wearable components used for this device are easily
available which increases the lifetime of the product. The cost of the device is
estimated to be low in an effort to help the most needed, this will allow the product
to de distributed in different areas of the world. When the apparatus is no longer
usable, the parts could become scrap metal and can be recycled, thus making the
product will cause minimal to none environmental impact.
Anna Steege
This project is particularly focused on improving the living standards of low-
resource countries. The simplistic nature of the mechanism is designed to be easy
to use and adaptable to its environment. Additionally, one of the goals of this
project centers on keeping the design and parts simple enough that someone
without training or experience could easily do maintenance on the device with
limited resources and tools. This would allow our product to improve the mobility
of persons with TF amputations while still allowing them the independence of
maintaining the device themselves. In this way, the device is sustainable within a
low resource setting. Additionally, all precautions are being taken to ensure that
the product will only improve TF gait. Extensive testing will be done to ensure
beneficial qualities before introducing this device to a new community for use. With
these considerations, the STEPS team strives to improve the quality of life of low-
resource countries through careful design and forethought.
Joseph Wilcox
The device developed by the STEPS senior design team was developed to
increase the stability and ease of use for transfemoral amputees. The device is
produced from easy to obtain and low cost materials that would have minimal
negative effect on the environment. The device will help amputees with mechanical
knees generate a more natural gait without needing an expensive electric knee.
Safety for the user was a high priority due to the nature of the human use of the
device. Future teams will work on improving the efficiency of the device to the point
that the device becomes a marketable product then start production of the device
to potential users.
4.2 PROFESSIONAL AND ETHICAL
CONSIDERATIONS
Andrew Adamo
The STEPS team has held professional design and ethical practice in highest
regard throughout the project development. All human testing was performed with
full disclosure to all participants and staff involved. Using safety measures such as
guided walking practice and a safety harness, the STEPS team ensured that any
subjects were treated with sensitivity and respect. The mechanical structure of the
device was designed with the safety of the end user in mind. By employing
adequate materials and inherent safety factors, the STEPS team owned the ethical
responsibility for the device throughout the design process. The STEPS team
communicated and worked in a professional manner with all internal and external
parties to best represent the University, project, and stakeholders.

Aaron Conrad
Safety was taken into account during design and testing phases and the
mechanical design was given a generous factor of safety. During testing phases,
participants were secured and harnessed to prevent injury. Even if the product
malfunctions and must be removed, there would be no damage to the original
prosthetic parts and removal would not reduce the user’s abilities from their state
prior to device installation.
Dolores Henson
Professional and ethical considerations in this project stem from the medical
impact of the project. Researching data pertinent to transfemoral amputees can
cause issues regarding how to discuss the psychological and physiological effects
of amputation. This is a sensitive subject, so it is important to be both
knowledgeable and respectful when discussing this type of medical condition.
Another consideration was how to keep subjects safe while testing. To solve this,
there was always at least one researcher with the subject at all times, and a
harness was used with treadmill walking to ensure a safe environment for the
subjects. Overall, the team performed ethically and did not face any major issues
throughout the schoolyear.
Joshua Kucera
As with any medical device, safety must be the supreme factor in both design and
testing. The STEPS team maintained a high level of safety in its testing by using
protective equipment during any trials that put the user at a substantial risk for
injury. The actual product was also designed with the safety of the final patient
leading the decisions. Cost was a secondary issue in areas such as material
selection and part configurations. The safety factors used in the design process
were meant to prevent as many catastrophic failure modes as could be foreseen.
In its business transactions, the STEPS team handled all purchase orders and
donation requests with respect and honor. It was clear from the beginning that
personal gain was not a focus of this project, and that standard was maintained
throughout the duration of the design process.
Professional and ethical considerations were thoroughly regarded throughout the
STEPS project. With the human subjects used in the testing, a full disclaimer was
given with all the potential side effects of wearing the simulator and testing
procedures. The safety and comfort of the subjects was maintained throughout
testing and by having at least one team member present for all tests and the
practice sessions with the simulator. The STEPS team members conducted
themselves in a professional manner in communication with vendors, donors,
faculty, and university staff.
Raul Saldana
Our device should undergo extensive testing to improve the design and ensure
that it performs its function as expected and advertised. If our device does not
perform as it is expected to, it is possible that the people using it could become
seriously injured. Our design also includes having our device inside an enclosure
to reduce the chances of malfunction of our mechanism, but it should also be noted

that it is a good way to keep children and animals from injuring themselves with
the mechanism of our device. Given that one of the main goals of our project is to
make our device affordable to third world countries, we should consider looking
into investors and funding agencies that would make it possible to give our device
to people in those third world countries for free.
Garret Senti
The professional and ethical considerations were thoroughly regarded throughout
the STEPS project. The team took measures to makes sure the device is usable
and does not harm the user while operating the device. The reliability of the device
and the safety of the user was tested by volunteers on the team to ensure that the
promised deliverables were upheld. It is important to the STEPS team to withhold
the professional and ethical guidelines to preserve our reputation as engineers and
Letourneau’s name.
Sonia Sosa Saenz
Since the completion of this one-year term required the use of human subjects to
test the efficiency of the device, professional and ethical considerations were
serious. The Institutional Review Board approved the testing protocol to be used
during the trials and the researchers enforced the subject security at all times. The
participation in the study was completely voluntarily and remained this way
throughout the different phases of testing. The team protected the identity of the
subjects during the completion of the study. The STEPS team upheld the code of
National Society of Professional Engineers (NSPE) ethics and executed the ethical
responsibilities stated in the 6 fundamental cannons as part of our formation into
credible engineers.
Anna Steege
The STEPS team is focused on improving the quality of life for those in low-
resource settings that do not have the opportunity to do this themselves. The team
will not receive any profit from this excursion, and what patent rights might be
achieved later will only benefit LeTourneau University, a university focused on
many forms of missions work. In this way the STEPS team is able to claim user
satisfaction and goodwill as a top priority. Additionally, the manner in which the
testing and development is conducted reflects the team's desire to respect and
strive for the highest safety standards. This involves rigorous safety measures and
full disclosure of potential risks to test subjects. Of course the safety of future users
is also considered with high safety factors built into the design of the product. In
short, the STEPS teams strives to take all measures to improve and maintain
professional and ethical considerations in the design of this device.
Joseph Wilcox
The STEPS senior design team thoroughly regarded the professional and ethical
considerations throughout the project. The safety of the user was held in the
highest regard for both the gait simulator and the device development throughout
testing. The subjects that tested the gait simulator and the device had at least one
other team member present. The device was engineered to cause no harm to the
user while in use. The STEPS team members conducted themselves in a
professional manner in all their communications with vendors, donors, team
members, faculty, and university staff.

5. INDIVIDUAL ROLES
5.1 RELATIONSHIP OF INDIVIDUAL ROLES
TO OVERALL PROJECT
Figure 5-1. STEPS Team Organization

5.2 INDIVIDUAL WORK DESCRIPTIONS
Sonia Sosa Saenz: Team Lead
During this year, I served as the Team Lead of this project. My overall
responsibilities were to delegate work among sub-team leads and maintain a
liaison between members of the project and the faculty advisor. More extensively,
my duties entailed to have regular meetings with the sub-team leads to ensure that
the project was going through the right path, have regular meetings with our faculty
advisor to update him in the project and to ask for task clarification as needed. I
was also in charge of overseeing/proofreading the Master Project Plan, Final
Report and end-of-the-semester Presentation along with the Documentation
manager. Since I am a biomedical engineer, I aided the testing team as if I was
one of the members in the sub team. For this position, I performed data collection
and processed collected data to obtain graphics for the Final Report and
Presentation.
Conclusion and Future Work
The Team Lead position is an important role in the project that involves much
responsibility and personnel management. The person with this title is expected to
be invested in the project and to dedicate a significant amount of hours towards it.
In addition, the Team Lead is supposed to help the Sub-Teams as needed and not
only oversee the work. It is recommended to keep in touch regularly with the sub-
team leads but also with the rest of the team to avoid tension and
miscommunication issues. In addition, delegation is essential for the successful
fulfillment of this position since there are many things to take care of at once.
Finally, the Team Lead should encourage the team members to do their best and
to use each member's strengths as best fit in the project. Overall, I had a good
experience of being responsible for this position. It was hard work and there were
many issues to be handled but having sub-team leads helped to decrease the load.
Throughout this experience, I learned meaningful skills regarding leadership,
management, conflict resolution, project scheduling, design process, conducting
research, and biomechanical testing.
Design Team
Andrew Adamo: Design Support
I was a member on the mechanical design sub-team responsible for creating and
editing Solidworks models, assembling and troubleshooting the beta prototype,
and interfacing with the testing team to ensure smooth implementation of the final
device. Given my absence during the first half of the project, my first duty was to
catch up to speed quickly so that I could be a contributing member of the team;
once this was completed I began providing key insights during the brainstorming
and modelling process. I modelled numerous components including the upper
flange, male prosthetic connector, and side arm supports; each of these models
integrated seamlessly into the overall assembly model. Following the completion
of the beta prototype, I assumed responsibility for organizing and proofreading the
beta prototype design process documentation.

My role on this team was both creative and supportive; using knowledge gained
from previous industry experience, I identified concepts which could be
economically and reliably manufactured and assembled. Throughout the design
and testing phase, I consistently identified errors and corrected them in a timely
fashion to keep the project on schedule. This supportive role was integral to the
success of the project.
Aaron Conrad: Finance Manager
I was appointed to handle the budget and assigned with the mechanical
engineering majors to the design aspects of the device. As Dr. Sasaki informed
me that there was not a fixed pot for the team, the budgetary responsibilities
involved setting up a spreadsheet that kept a running total of expenses for the
team to compare the expenditure to expected spending. The spreadsheet was to
be regularly updated as I was given information on receipt for moneys that were
charged to or reimbursed by LeTourneau University. As a member of the design
team, I devised and made digital models of numerous original and novel concepts
for device parts to be selected by the team for a final solution. Additionally, I
oversaw fabrication, locating a shop and submitting designs for parts the team
needed. The machine component and design laboratory on campus does have
proper equipment for cutting thick sheets of metal.
Attending the financial situation of the team was a necessity. Further, without a
broad consideration of potential solutions, the device could not have taken the form
embodied in the final prototype. Finally, without having parts fabricated the
prototype could not have been constructed for the durability necessary for testing.
Joshua Kucera: Design Sub-team Lead
I was the Design Sub-Team Lead for the STEPS Senior Design project. My duty
was to oversee and guide the design process from start to finish, ultimately
delivering a final product that met all given requirements in an efficient and simple
manner. As the Design Lead, I was responsible for effectively delegating tasks to
my team, which naturally entails clear communication of expectations and the
foresight for scheduling deadlines. Aside from this management, I personally
contributed heavily to concept generation and selection, CAD modeling, material
calculations, part specifications, fabrication, and troubleshooting. I was present for
the majority of device testing to ensure proper setup and analyze potential
improvements to the device under actual usage. Additionally, I served as the chief
editor of all mechanical documentation for the final report. I also had the unique
task of generating models of our device that are compatible with OpenSim for use
in the Testing team’s analysis and presentation of results.
My role was crucial to the end result of the project. The deadlines and oversight I
provided, as well as my substantial contributions to design work, served as the
backbone of the design process. I would argue, though, that in an ideal case my
role would have been much more organizational in nature and there would be less
of a need for my direct involvement in most areas. For future teams, it is important

to stress that two-way communication is key to successful cooperation, especially
for a project that is so interdependent on its separate parts. An assignment is the
responsibility of its owner, and unless otherwise stated it is assumed that the owner
is fully capable of completing it without assistance and that it will be done on time.
This standard should be made clear as early as possible.
Garret Senti: CAD Design & Assembly Manager
My role as CAD Designer and Assembler for STEPS is comprises of designing
components for the prosthetic and constructed the prototype from the
manufactured SolidWorks models. This included designing, building, and testing
the prototype. I worked with the mechanical engineers to take the requirements
and ideas of the team to develop a representation of what the prototype is
supposed to be. I also performed analyze on what could happen based on the
conditions established and the effects that occur in a real life situation. With the
teams’ help, I contributed to the assembly of the device by gathering the
components and making modifications to parts that were not designed correctly.
For testing, it was a duty to make sure that the changes made helped the
performance and data collection of the user and calibrating the system to the
correct setting to get the most out of the device. Lastly, I assisted with the writing
of the final report to talk about the prototypes designed, the strengths and
weaknesses of each one, and the improvements that should be made.
I understand the importance of a designer and how the models generated help
identify issues that need to be addressed as well as the importance of an
assembler to take what was fabricated into a functional prototype. It is important
to note that not everything created in the model will turn out exactly as what is
expected and not everything can be analyzed theoretically but can be determined
through trial and error.
Joseph Wilcox: Mechanical Lead
I was the Mechanical Engineering lead for the STEPS Senior Design Team. My
jobs for the first semester was to help the mechanical engineers work with the
biomedical engineers, lead the construction of the TPG Simulator, and help with
the design and construction of the Alpha prototype. For the second semester my
job was to help the Design Sub-team with the construction of the Beta prototype.
Also I caught whatever fell in no one’s job description or if people needed some
help. This included designing, calculating failure, construction, writing, machining,
and testing of our devices.
My role would have been better used if we separated the design team into two
separate units either working on the same problem or working on different
problems. As it was the first semester where I and a few other team members
would break off too work on the TPG Simulator while the main group was working
on the device design, yet those that broke off to work on the TPG Simulator would
also come back and work on the device as time allowed.

Testing Team
Anna Steege: Testing Sub-team Lead
I served as Testing Sub-Team Lead during this endeavor. In this position I was
responsible to organize all activity involved in testing the device the team created.
This involved acting as a pilot subject when the simulator and the device were in
the design phases. In this early period, I assisted the mechanical sub-team by
researching manufactures and various vendors to create our prototype and to
purchase necessary results. With the help of the team, I created testing procedures
and implemented them in the later phases of our product. This involved acting as
a subject and assisting other subjects with their trials. I also coordinated the
documentation of our results and the creation of all testing-related documents,
graphs, and charts for the final report. Finally, I acted as the representative for the
testing sub-team during the formal presentations of our project.
This position was essential to the team's success in that it served to centralize all
testing efforts under one primarily leadership. In this position, the Team Lead could
exercise better control over the project in being able to trust the Sub-Team Leads
to achieve and drive the whole group to success. It allowed good communication
among team members, with the Team Lead, and with the Faculty Advisor. I would
stress the importance of scheduling out the entire project early on to have self-
selected deadlines to strive for. This greatly benefited the team's drive and
commitment to the project.
Dolores Henson: Public Relations Manager
Within the STEPS team project I held the position as the Public Relations Manager
as well as being a member of the testing team. The public relations of this team
included writing letters to potential donors in order to fundraise for the project as
well as sending thank you notes to donors. I also was in charge of designing
comprehensive semester presentations and a poster to showcase the project. The
public relations role was important to the success of STEPS since many parts
needed to be outsourced throughout the project. The fundraising letters sent out
in the Fall 2017 semester brought about $1800 into the account for this project
which allowed the team to have freedom of choosing the parts they needed without
having cost be a major hindrance. On the testing team, I specialized in EMG and
marker placement on subjects for motion capture trials along with helping data
processing after capturing. I also conducted V02 tests with all subjects during the
semester. Lastly, I was the first author of a poster abstract submitted for the
American Society of Biomechanics national conference. Being a part of the testing
team was helpful because of the numerous trials required in order to show the
success of the device produced by the team.
The presence of a public relations director helps finance the project which is critical
with respect to prosthetic parts, which are sometimes difficult to retrieve due to
price or lack of proper licensing. Also a large testing team is useful with multiple
subjects and trials in order to get things done in short amounts of time by spreading
out work to a trusted team. This role as a whole was a positive piece moving within
the team in order to achieve success.

Jessanne Lichtenberg: Documentation Manager
As the documentation manager for STEPS, my main work centered around the
overseeing the Master Project Plan and the Final Report. The role also included
supervising the overall documentation of the design, embodiment, and testing of
the project. I worked with the team lead and sub-team leads to plan out the various
aspects of documentation. I communicated with team about the sections that
needed to be completed and the deadlines. I performed literature searches for
various parts of the project. I reviewed all documentation for quality, thoroughness,
and cohesiveness. During the project term, I took meeting minutes and reviewed
emails with vendors and donors. I helped write a poster abstract for the American
Society of Biomechanics national conference. In addition to documentation, I had
a role on the testing team. I acted as a subject and assisted with testing other
subjects. I helped with background research for developing the testing protocol,
and data processing in Matlab.
Overall, I believe being documentation representative was helpful for the team to
organize and manage the records and reports of the project. It was beneficial to
allow the sub-team leads to delegate writing tasks within their sub-teams and for
me to review and help as needed. I would recommend Vicon being installed on
more computers in the lab to speed up data processing. Also, having a clear data
processing plan is vital to efficient time management of members.
Raul Saldana: Data Processing Manager
I served as the data processing manager on the STEPS team. I was tasked with
processing all 3D motion capture data and preparing it for use in MATLAB and
OpenSim. I assisted with data collection and the acquisition of joint angles from
each subject. I calibrated the 3D motion capture system and assisted in the
preparation of the markers. During the first semester, there was very little motion
capture data collected and I did not need to spend a large amount of time
processing the data. I assisted with literature research and pilot testing for
developing our testing protocol for measuring energy expenditure using oxygen
consumption.
The role of data processing manager is an important one as the processing quality
of the motion capture data directly affects the accuracy of the results acquired from
testing. It is important to have accurate results in order to properly assess our
device. I think it would be helpful to have NEXUS installed on the other computers
in the lab so that multiple people can process data at once if needed. It is also very
important that the calibration of VICON is done well to get high quality data.

6. OVERALL PROJECT DEVELOPMENT
The overall project was divided into two main phases, design and testing. A
schedule of the major tasks for each sub-team is found in a Gantt chart in Appendix
A.
The design team was responsible for the fabrication of the TPG simulator and the
two prototypes created. The testing team was responsible for establishing and
executing tests to evaluate the efficacy of the STEPS device. The two sub-teams
worked in communication with each other throughout the design process to ensure
their design was feasible with testing methods.
6.1 TRANSFEMORAL PROSTHETIC GAIT
SIMULATOR
6.1.1 Purpose
The TPG Simulator is made from a metal frame, brace, knee, pylon, and foot (see
Figure 6-1). Its purpose is to allow a non-amputated subject to walk in a manner
comparable to amputee gait. The socket had two major parts: the knee brace, and
the metal frame. The brace functioned as the main anchoring structure for the
metal bracket and kept the subject's knee locked to 110° flexion. The metal bracket
provided a rigid connection to the prosthetic knee. Multiple lengths of pylon were
made so that the simulator could be used with test subjects of varying heights. In
addition, two spacers were fabricated from remaining aluminum pylon to increase
the capacity for height variability. The foot, which was included in the purchase
from LIMBS International (El Paso,TX), attached to the base of the pylon in the
same manner as a clinical prosthetic. The complete fabrication of the TPG
Simulator can be found in Appendix B.
Figure 6-1: Transfemoral Prosthetic Gait Simulator

6.1.2 Validation
A literature review was performed on other transfemoral prosthetic simulators.
From a comparison of the team’s TPG simulator joint angles and EMG data to
those found in literature, the team concluded that the fabricated TPG simulator
was effective in mimicking TFA gait. A poster abstract was written for the American
Society of Biomechanics about the effectiveness of the TPG simulator. The
abstract can be found in Appendix C.
6.2 DESIGN & EMBODIMENT
6.2.1 Alpha Prototype
6.2.1.1. Concept Selection
The team generated three concepts for the alpha prototype: a clutch plate, a
ratchet, and an internal ratchet.
Clutch Plate Concept (Figure 6-2)
The clutch plate concept was an air bladder attached to the foot which would
deflate during stance phase causing the clutch plates to contact one another.
When this occurred, flexion would be prevented.
Figure 6-2. Model of Clutch Plate Concept in Solidworks
Ratchet Concept (Figure 6-3)
The ratchet concept used pressure applied to a foot switch to engage a ratcheting
gear mechanism at the knee which would prevent flexion, but allow extension.

Figure 6-3. Model of Ratchet Concept in Solidworks
Internal Ratchet Concept (Figure 6-4)
The internal ratchet concept was acted the same as the ratchet mentioned
before, except instead of the gear teeth on the outside they are on the inside of
the circle with an internal pawl to stop flexion.
Figure 6-4. Model of Internal Ratchet Concept
The below decision matrix (Table 6-1) identified the ratchet as the most feasible
concept to meet the project's requirements.

Table 6-1. Decision Matrix
6.2.1.2. Design
The resulting design consisted of four main parts: the gear, ratcheting pawl,
tension cable, and foot switch. As a system, they formed a device which provided
a rotational locking force to stabilize the knee when it is in partial flexion. When
the subject transfers weight off the foot switch during swing phase, tension is
applied to the cable and the pawl is disengaged. When the subject transfers
weight onto the foot, tension is released from the cable which allows the pawl to
mesh with the main gear teeth and lock further flexion. The breakdown of the
alpha prototype can be found in Appendix D.
Gear and Pawl (Figure 6-5)
The device for the ratchet includes a longitudinal spring which connects the pawl
and the metal plates on either side. The gear is rigidly fixed to the upper
connection and pin-connected to the metal plates on either side. A tension cable
is connected to the pawl to engage and retract the teeth of the pawl from the
gear. By applying tension to the cable, the device is able to rotate, but when
there is no tension the spring locks the gear and pawl teeth together allowing
only extension.

Figure B-5. Alpha Prototype: Gear and Ratcheting Pawl
Foot Spring and Tension Cable (Figure 6-6)
The design for the pressure plate includes compression springs that connect to
the foot and a plate with a tension cable connected to it. Depending on the state
of the springs (i.e. compressed or expanded), the tension in the cable will vary.
When no force is applied to the plate, the tension cable will be pulled downward,
retracting the pawl so that the knee can swing freely. Conversely, when pressure
is applied to the plate, slack is allowed to develop in the cable and the linear
spring on the pawl pulls it in to engage with the gear teeth. The gear engagement
causes the mechanism to lock against flexion.
Figure B-6. Alpha Prototype: Foot Spring and Tension Cable

6.2.1.3. Embodiment
The design concepts involved in the alpha prototype focused on a ratcheting
mechanism installed on the prosthetic knee and a mechanical switch beneath
the prosthetic foot that actuated the ratcheting mechanism. The alpha prototype
design was meant to be a “Proof of Concept” which ensured that the theoretical
concept of the invention could be carried out. The primary consideration in
designing the device was the durability of the gear teeth in the ratcheting
mechanism to support the user's weight. The secondary consideration was
ensuring that the springs in the prosthetic foot switch were strong enough to
support the user's weight without being overly strong such that the ratcheting
pawl could not engage with the ratcheting gear.
With the concepts chosen, the primary concerns in fabrication were ease of
installation and compatibility to different mechanical knees. The ratcheting pawl
and gears were water-jet cut by a local manufacturing company.
6.2.1.4 Assembly
The gear and pawl pairs were held together by a slotted aluminum bar, and a
spring held the ratcheting pawl to the main gear (Figure 6-7). A steel cable ran
from each ratcheting pawl to the prosthetic foot switch. The prosthetic foot switch
included four to six springs, depending on the user's weight, sandwiched
between two steel plates. The upper plate was attached to the heel of the
prosthetic foot with a sheet of hook-and-loop fasteners and the bottom plate was
attached to the steel tension cables with two holes and secure knots. To attach
the stemmed gears to the prosthetic knee, the team crafted bent flanges from
steel plates that were each bolted to the gears' stems. The flanges were bolted
to a mounting apparatus involving a characteristic male-to-female prosthetic
pyramid adapter, which held the TPG simulator to the prosthetic knee.
Figure B-7. Assembled Alpha Prototype with TPG Simulator

6.2.1.5. Calculations
As part of the design process for this device, calculations were performed to
ensure that the pieces made would not fail under the loosely defined loading
conditions. Given the extreme level of ambiguity in both usage scenario and
environment, a safety factor of 4 was used to effectively eliminate any chance of
failure before the concept's feasibility could be properly evaluated. The
calculations performed served to develop a life expectancy of the device and
determine the required stiffness of the spring components for the alpha
prototype. (See Alpha Calculations in Appendix E)
6.2.1.6. Conclusion
The essential proof of concept was successful. The attachment mechanism held
the device securely in place while the pawls and gears prevented flexion in the
knee joint when engaged. The tension cable allowed the pawls to actuate to and
from the stemmed gears. The foot switch was capable of generating sufficient
displacement for the pawls to disengage from the gears. The main issues with
the device were the attachment flanges bending after extended usage and the
sensitivity of the tension cable to minor adjustments, which could cause the
device to remain either engaged or disengaged.
The following necessary improvements were noted during preliminary testing of
the alpha prototype.
 Enhance adaptability of the system
 Reduce gear friction
 Minimize impact on gait
 Reduce device weight
 Increase pawl engagement consistency
6.2.2 Beta Prototype
6.2.2.1. Introduction
The STEPS device’s transition from the Alpha to the Beta prototypes involved
systemic alterations to the switching mechanism. Where the Alpha prototype
employed a foot-mounted switch with makeshift components, the Beta prototype
included a more sophisticated and well-assembled ankle switch. The switch
location was changed in an attempt to intercept all force traveling through the
pylon regardless of the center of pressure on the foot. This change added several
design considerations, the most prominent of which were: inhibiting unwanted
rotation, minimizing the total length added to the prosthetic leg, as well as
ensuring reliable and smooth motion while retaining stability. Aside from the
switch adaptations, the gear and pawl assembly was also modified to be more
streamlined, repeatable, and reliable. This was accomplished by designing the
upper flange to be one seamless piece to enhance rigidity and reduce tolerance
error. In an attempt to make the engagement/disengagement of the device more
reliable, the Beta prototype utilizes a linear pawl instead of the rotational variation
of the Alpha.
The Beta prototype is broken down into two main subsystems: a ratcheting pawl
assembly and an ankle anti-rotation assembly; these two subsystems comprise
a device which is fully external to the passive prosthetic knee. For a visual

representation of the device, see Figure 6-8. The breakdown of the beta
prototype can be found in Appendix F.
Figure B-8. Assembled Beta on TPG Simulator
6.2.2.2. Design & Embodiment
1. Ratchet and Linear Pawl
The ratcheting flange is a set of partial gears machined out of a single piece of
steel plating. The ends of the plating are bent 90° to form its final three-
dimensional shape (Figure 6-8). The plate is designed with a central hole that
allows it to fit over the male pyramid adapter on the knee module and anchor on
two small pins to prevent rotation. The lower portion of the ratchet is composed
of four struts, two on each side, that attach to either side of the bent gear flange.
These struts have specific slots cut into them that allow the pawl to be mounted
between them using pins. The pins constrain the motion of the pawl to be strictly
linear. The upper pin on the pawl is connected to both an extension spring above
and a tension cable below, such that the spring is constantly pulling the pawl to
an engaged position with the gear flange. The tension cable is connected to the
ankle-switch, which will pull down when no weight is applied and retract the pawl
from the gear flange by pulling against the extension spring with a higher
magnitude of force. Therefore, the mechanism will lock against flexion when
there is weight applied to the ankle switch, but will unlock when no weight is
applied as the ankle switch expands to return the joint to a free and unhindered
state.

2. Anti-Rotation Switch System (Figure 6-9,10)
The anti-rotation switch system is composed of
four uniquely designed parts and mounted in the
pylon at the ankle. Figure 6-9 shows these
components and the visuals mentioned in this
paragraph refer to that diagram. The first
component is a simple cylinder design, highlighted
in blue, that mounts inside the clamp of the female
pyramid connector and serves as the static lower
anchor for three dowel pins. These dowel pins are
the second element and were specially modified to
the proper length. The pins mount vertically on the
lower cylinder and move through the bronze
bushings mounted in the third element. This third
element is an insert in the pylon, statically mounted
with set screws so it cannot rotate (Figure 6-9-c).
The dowel pins slide linearly through the bushings
mounted inside this piece, which limits the motion
of this switch to be completely vertical. The upper
end of the dowel pins are then rigidly connected to
another cylindrical endcap (Figure 6-9-b). This
fourth component also has horizontally-tapped
through holes that align with slots (Figure 6-9a),
cut into the pylon itself. Eyebolts are screwed into
these holes from outside the pylon and become the lower attachment points of
the tension cable (Figure 6-9-d). Finally, a spring is added between the foot and
the pylon which surrounds the dowel pins and provides the force necessary to
keep the switch extended when no weight is applied.
A full detailed fabrication procedure can be found in Appendix G.
Figure B-10. Beta Prototype: Anti-Rotation Switch System with the Dowels(left),
Pylon Insert (middle), and Upper Endcap (Right).
Figure B-9. Anti-Rotation Switch
System.

3. Locking Mechanism (Figure 6-11)
When weight is transferred to the prosthetic leg, the spring force will be overcome
to compress the switch and bring the foot closer to the knee. This pushes the
eyebolts up to create slack in the tension cable which results in the engagement
of the pawl and the ultimate locking of the knee ratchet. As weight is taken off
this leg, the main spring will expand to create tension in the cable and release
the pawls from the gear flange to allow the knee to swing freely.
Figure B-11. Beta Prototype: Locking Mechanism
6.2.2.3. Calculations
Using insight gleaned from the alpha prototype performance, the team focused
on minimizing the complexity of the device while maintaining stability and
longevity. With these priorities in mind, the team performed calculations to
determine optimal spring stiffness at the ankle, and maximum stress, friction, and
torque at the gear teeth. To ensure longevity, the team conducted fatigue
calculations to identify the point of material failure under standard use. A safety
factor of 2.5 is employed to account for unknowns and prevent premature
component failure. Many of the calculations used during the design of the Beta
are similar or identical to the Alpha calculations. (See Beta Calculations in
Appendix H)
6.2.3 CONCLUSION
Overall, the STEPS beta prototype demonstrated significant improvement over the
alpha prototype in the areas of reliability and manufacturability. Through a detailed
design and troubleshooting process, the team developed a device which provided
consistent anti-buckling torque during stance phase. A complete Bill of Materials
and detailed Solidworks drawings can be found in Appendix I and Appendix J,
respectively. The most prominent success of this year's project work was the
production of a consistently reliable prototype that the testing team could use for
detailed scientific evaluation. For a first year project this device shows excellent
potential for continual improvement in the areas of versatility and adaptability. For
a complete breakdown of the suggested improvements to the device, refer to
Chapter 7.

6.3 TESTING & VALIDATION
6.3.1 Overview
Three college students of different height, weight, sex, and physical fitness were
recruited for testing. All subjects had no prior experience with the TPG simulator
or the device. Demographic Table can be found in Table 6-2.
All subjects wore the TPG simulator on the dominant, right leg for all trials. This
was considered to be the “affected” limb, and the left leg was referred to as the
“intact” limb.
To standardize the proficiency level of the subjects in walking with the TPG
simulator, a learning time was used. In the study by Wentink et al. [18], the
average gait speed of a unilateral TF amputee was 60% of an individual with no
impairment. Therefore, proficiency was achieved when 60% of their normal gait
speed was reached while walking with the TPG simulator.
Subject 1 Subject 2 Subject 3
Gender Female Female Male
Age (yrs) 22 21 21
Height (cm) 162.6 130 172.7
Weight (kg) 54.4 59 87.5
Acclimatization Time
to TPG Simulator (hr)
1.5 3.25 1.5
6.3.2 Data Acquisition Methods
6.3.2.1. Kinematics, Ground reaction forces (GRF) & Muscle Activation (EMG)
Preparatory Methods
Control Trials
64 reflective markers were attached to anatomical landmarks of the pelvis, legs,
feet, and torso (see Appendix L). The markers provide accurate motion tracking
by the VICON system (T10, VICON, Oxford, UK). The kinematic data was used
for further analysis of joint angles (see 6.3.3.1.).
Four wireless surface EMG electrodes (Trigno, Delsys Inc., Natick, MA) were
placed on the dominant limb muscles: the iliopsoas, rectus femoris, gluteus
medius, and semitendinosus [14]. The electrode placement can be seen in
Appendix M.
TPG Simulator trials
These trials used markers only on the lower body. The marker set was changed
from the set originally used in the control trials because of the difference in data
processing that will be explained further in Joint Angle Data Processing. 34
reflective markers were attached to anatomical landmarks of the pelvis, legs and
Table B-2: Subject Demographics

feet. Below-knee markers were placed on the TPG Simulator in place of the
subject’s dominant limb.
Four wireless surface EMG electrodes were placed on the same muscles as the
control trials excluding the iliopsoas, which was replaced with the tensor fasciae
latae. This change was due to the small output signal generated from the
iliopsoas, and the accessibility of comparison data in existing literature [14].
TPG Simulator with STEPS Device trials
The same lower body marker and EMG placement set was used for the TPG
Simulator with STEPS device trials than the one used for the TPG Simulator
trials. This was done to maintain consistency with the difference in data
processing as explained later in Joint Angle Data Processing. 36 reflective
markers attached to anatomical landmarks of the pelvis, legs and feet including
the simulator and device were used. Two extra markers were added in the
Prosthetic Limb to aid in the gap-filling process of data.
Data Collection
Using a motion capture system with seven infrared cameras (T10, VICON,
Oxford, UK), kinematic and ground reaction force data (FP4060-08, Bertec
Corporation, Columbus, OH) were captured at 1 kHz during 6-m walk aiming for
constant velocity in throughout all the trials. The speed was kept constant using
an electric metronome set to 92 bpm, which represents approximately 0.89 m/s.
One subject walked a 30 m track to a metronome set to 90 bpm and that speed
was found to be .87 m/s. The next velocity still comfortable for this subject on
the simulator was 92 bpm which corresponded to .89 m/s for this subject in
particular. This subject has the slowest walking speed compared to the others,
so this was the deciding factor in using this speed. The selected target speed
was comparable to previous studies using mechanical knees [30], showing self-
selected speeds at or near 1.0 m/s. EMG signals from four wireless surface
electrodes were recorded simultaneously with the kinematic and kinetic data.
These signals were sampled at 1 kHz.
With only two force plates available, it was necessary to run each trial twice,
once with the affected limb leading, and then with the intact limb leading. This
process was repeated to obtain three full gait cycle samples for control data and
five full gait cycle samples for the TPG Simulator and TPG Simulator with STEPS
device. Each side led for three trials, which produced a total of six trials per
subject for control data. For the remaining sets of data, each foot led for five
trials, producing a total of 10 trials per subject.
The sets of trials were collected in the following order for all subjects: Control
trails, TPG simulator, TPG Simulator with STEPS device. It was not possible to
randomize the order of data collection because the STEPS device was not
available at the beginning of the testing period.
6.3.2.2 Oxygen Consumption
From the literature review, the team discovered that TFAs, despite being self-
described as generally physically fit, use a larger percentage of their maximal
aerobic capacity than healthy participants to perform normal activities of daily life
[4]. Therefore, it was determined that oxygen uptake level adjusted to body

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