Improving Mediolateral Walking Balance With an Assistive Exoskeleton
Phase: NA
Conditions: Stroke
Sponsor: Medical University of South Carolina

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PROTOCOL TITLE: Improving Mediolateral Walking Balance with an Assistive Exoskeleton 
 
PRINCIPAL INVESTIGATOR: Jesse Dean, PhD 
 
1.0 
Objectives / Specific Aims 
The purpose of this study is to investigate the potential of exoskeleton assistance to 
improve walking balance using methods that will be accepted by people with stroke. The 
first specific aim is to characterize the effects of exoskeleton balance assistance on 
unperturbed walking. The second specific aim is to characterize the effects of exoskeleton 
balance assistance on perturbed walking.  
We hypothesize that exoskeleton assistance will strengthen the relationship between step 
width and pelvis displacement relative to the stance foot, an important biomechanical 
strategy for ensuring walking balance. We anticipate that this relationship will be 
strengthened during both unperturbed and perturbed walking. 
 
2.0 
Background 
Numerous exoskeletons have been developed with the goal of assisting walking,1 including 
some available to consumers.2 However, most devices (Ekso, HAL, Indego, ReWalk) do 
not assist balance,2 preventing normal use of the arms by requiring users to rely on 
walkers, crutches, or canes. Alternatively, a few devices (Atalante, Rex) prevent falls by 
essentially carrying patients around,2 rather than assisting strategies normally used to 
ensure balance. This approach is not viewed favorably by many patients, who would 
instead prefer an “exoskeleton to assist and correct their movement rather than walking for 
them”.3 While some early-stage work has developed exoskeleton control strategies that 
improve balance responses to anteroposterior pushes or slips,4,5 mediolateral balance has 
been largely neglected despite its importance for gait stability and fall prevention.6–9 We 
will test whether exoskeleton assistance can restore the normal mediolateral gait 
stabilization strategy of adjusting step width based on real-time pelvis dynamics.  
Beyond the ability of an exoskeleton to alter gait mechanics, it must be accepted by users – 
which is unlikely if a device is perceived to make walking more difficult or otherwise 
interfere with the intended gait pattern.3 This is a particular concern with balance, as 
individuals at a risk of falls are often resistant to changing their walking pattern,10 likely 
because unfamiliarity is perceived as risky. Here, we will assess physiological and 
psychological indicators of participants’ acceptance of the exoskeleton assistance.  
In summary, despite the critical importance of walking balance, assistance of mediolateral 
balance is largely limited to walkers and canes that must be controlled with the arms, 
limiting performance of real-world tasks. The proposed work will address this gap through 
testing of an assistive control strategy based on a mechanistic understanding of walking 
balance. 
 
 
 

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3.0 
Study Endpoints 
Our primary outcome measure will be the partial correlation between step width and pelvis 
displacement at the start of a step (ρSW).11 Secondarily, we will quantify the average 
bilateral gluteus medius activity during the stance and swing phases of the gait cycle. We 
will also quantify Rating of Perceived Stability12, a validated psychological measure of 
balance difficulty. Finally, for trials in which mediolateral pulls are applied, we will 
quantify the change in mediolateral foot placement relative to unperturbed steps.  
 
4.0 
Inclusion and Exclusion Criteria/ Study Population 
Participants will be recruited from an MUSC database containing the contact information 
of stroke survivors who have agreed to be contacted for research participation 
(Pro00037803). Initial screening will be performed by study staff through a phone call to 
confirm basic participant characteristics (e.g., timing of stroke) and interest in research 
participation. The ability of potential participants to meet the more detailed inclusion and 
exclusion criteria will subsequently be determined in person. 
Inclusion Criteria  
• 
Evidence of a stroke at least 6 months prior to participation 
• 
Evidence of dysfunction of the paretic lower limb (Fugl-Meyer lower extremity 
motor score < 34) 
• 
At least 21 years of age 
• 
Self-reported experience of a fall in the previous year, and/or a fear of falling 
• 
Gait speed of at least 0.2 m/s 
• 
Ability to walk on a treadmill without a cane or walker 
• 
Ability to follow three step commands and communicate with experimenters to 
answer questions (e.g., regarding their balance confidence) 
• 
Provision of informed consent 
Exclusion Criteria 
• 
Resting blood pressure higher than 220/110 mm Hg 
• 
History of unstable cardiac arrhythmias, hypertrophic cardiomyopathy, severe 
aortic stenosis, angina or dyspnea at rest or during activities of daily living 
• 
Preexisting neurological orders or dementia 
• 
Legal blindness or severe visual impairment 
• 
Presence of neglect 
• 
History of DVT or pulmonary embolism within 6 months 
• 
Uncontrolled diabetes with recent weight loss, diabetic coma, or frequent 
insulin reactions 
• 
Orthopedic injuries or conditions (e.g., joint replacements) in the lower 
extremities with the potential to alter the gait pattern 

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We plan to include a diverse participant population, paralleling the general demographic 
characteristics of the Charleston area. This will be accomplished using the database referenced 
above, which currently contains contact information for over 1000 individuals. We will not 
exclude any sex/gender or racial/ethnic group. This study will not involve any special classes of 
subjects, including fetuses, neonates, pregnant women, children, prisoners, institutionalized 
individuals, or other vulnerable populations. Children will not be included because this study 
focuses on individuals who have experienced a stroke. This is rare among children, and would be 
expected to involve a different mechanism or pattern of recovery. 
 
5.0 
Number of Subjects 
A total of 21 individuals with chronic stroke will be recruited, all locally. 
 
6.0 
Setting 
All research, including all recruitment, data collection, and data analysis, will be performed 
at the MUSC College of Health Professions Research Building at 77 President St. 
Charleston, South Carolina. North Carolina State University received the center grant 
funding that supports this center subproject, but is not otherwise involved in conducting 
the research that is part of this study. 
 
7.0 
Recruitment Methods 
This study will recruit from the Registry for Stroke Recovery (RESTORE-Pro#00037803, 
IRB approved 9/6/14), which is a research tool sponsored by the National Institutes of 
Health (NIH) Center of Biomedical Research Excellence (COBRE) in Stroke Recovery 
with subjects consented for future contact to support stroke recovery research conducted at 
MUSC.  RESTORE staff will query the registry for potential subjects and provide the 
Principal Investigator (PI) with the contact information of subjects who meet their criteria.  
The PI or research staff will contact subjects to further screen for potential enrollment.   
 
8.0 
Consent Process 
Informed consent will be obtained from participants prior to participation, using a form 
approved by the MUSC IRB. Participants will first be informed of the purpose of the 
experiments and possible risks. A member of the study staff will then review the Informed 
Consent form with the potential participant, ensuring they are given adequate time to 
review the document. The potential participant will be asked if they have any questions 
about the study, and asked if they agree to participate. The Informed Consent form will be 
signed by the participant. Copies of the signed forms will be given to the participant. The 
consent process will take place in a private room in the MUSC College of Health 
Professions Building. There will be no set period between informing the prospective 
participant and obtaining the consent. Participants will be reminded that they may end their 
participation in the study at any point.    
 
 

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9.0 
Study Design / Methods 
A total of 21 people with chronic stroke will be recruited for this study. The study will 
consist of four experimental sessions: Session 1A, Session 1B, Session 2A, and Session 
2B. 
Session 1A. A trained study team member will assess participants’ general function using 
several common clinical assessments: 
• Functional Gait Assessment: a test of walking balance 
• Lower Extremity Fugl-Meyer motor score: a test of leg motor function 
• Activities-specific Balance Confidence scale: a questionnaire about balance 
confidence 
• Fall history questionnaire: a questionnaire about participant’s self-reported fall 
history and fear of falling 
• Psychosocial Impact of Assistive Devices scale: a questionnaire about the effects of 
an assistive device on functional independence, well-being, and quality of life 
For familiarization, participants will don the exoskeleton to be assessed in this study 
(described in the Devices section below). Participants will perform four 2-minute treadmill 
walking trials at their self-selected speed while wearing the exoskeleton, which will 
alternate between not applying forces (transparent mode) and applying assistive forces to 
help appropriate foot placement location when talking a step.  
Session 1B. Participants will perform ten 2-minute treadmill walking trials at their self-
selected speed. Two trials will be performed for each of five conditions: 
• No Exoskeleton. The participant will not wear the exoskeleton. 
• Zero Impedance. The participant will wear the exoskeleton, but it will not provide 
the user with assistance or resistance. 
• Low Impedance. The exoskeleton will assist participants in placing their foot in a 
mechanically-appropriate location when stepping, with a stiffness of 0.1 Nm/deg 
and damping of 0.01 Nm/deg*s. This assistance is weak, essentially “nudging” 
participants toward the target foot placement. 
• Medium Impedance. The exoskeleton will assist participants in placing their foot in 
a mechanically-appropriate location when stepping, with a stiffness of 0.2 Nm/deg 
and damping of 0.02 Nm/deg*s. This assistance is moderate, as it will be noticeable 
to participants, but could still be resisted. 
• High Impedance. The exoskeleton will assist participants in placing their foot in a 
mechanically-appropriate location when stepping, with a stiffness of 0.3 Nm/deg 
and damping of 0.03 Nm/deg*s. This assistance is strong, as it will essentially 
enforce the target foot placement. 
After completing the walking trials in Session 1B, participants will complete the Modified 
ASSET Psychosocial Measure, a questionnaire that asks participants questions about the 
exoskeleton. 
Aim 1 experiments (Sessions 1A and 1B) for all participants will be completed before 
progressing to Aim 2 (Sessions 2A and 2B). Therefore, we anticipate that many 
participants will experience an extended time between Sessions 1B and 2A. 

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Session 2A. This session will repeat the procedures for Session 1B, serving to identify 
each individual participant’s optimum assistance level for subsequent use in Session 2B.  
Session 2B. Participants will perform ten 2-minute treadmill walking trials. In one trial, 
participants will not wear the exoskeleton. The remaining nine trials will consist of every 
combination of three exoskeleton conditions and three perturbation conditions. 
The exoskeleton conditions are: 
• Zero Impedance. The participant will wear the exoskeleton, but it will not provide 
the user with assistance.  
• Group Optimum Assistance: The exoskeleton will provide assistance using the 
parameters found to produce the largest group-average positive effect in Aim 1. 
• Individual Optimum Assistance: The exoskeleton will provide assistance using the 
parameters identified as optimum for each individual participant in Session 2A. 
The perturbation conditions are: 
• Speed Perturbations: The treadmill speed will follow a sinusoidal pattern, gradually 
changing from 0.2 m/s less than their self-selected speed to 0.2 m/s greater than their self-
selected speed and back over a period of 20 seconds. 
• Vision Perturbations: While walking, participants will turn their heads to look at 
visual targets 45o to the left and right of their heading direction, as cued every 10 
seconds.  
• Mediolateral Pull Perturbations: While walking, participants will experience 
mediolateral pulls delivered at the level of the sacrum13. These perturbations will be 
delivered at the start of the swing phase with a peak magnitude of 12% body weight 
and a duration of 200 ms.  
To eliminate the risk of participants falling while experiencing perturbations, participants 
will wear a harness attached to an overhead rail during all treadmill and overground 
walking trials. This harness will not support body weight, but would prevent participants 
from falling in the case of a loss of balance. The adhesive used to secure the LED markers 
and EMG electrodes to the skin may produce the risk of minor skin irritation. We will 
reduce this risk by asking participants if they have had any previous experience of skin 
irritation in reaction to specific gel or tape types, and by checking the participants’ skin 
after each experiment.  
In return for participants’ time and effort, they will be paid $200 for participation in the 
study. If they do not complete the study, they will be paid $50 for each completed visit. 
Payments that participants receive from MUSC for participating in a research study are 
considered taxable income per IRS regulations. Payment types may include, but are not 
limited to: checks, cash, gift certificates/cards, personal property, and other items of value. 
If the total amount of payment a participant receives from MUSC reaches or exceeds $600 
in a calendar year, they will be issued a Form 1099. 
 
10.0 Data Management  
For Aim 1, all statistical comparisons will involve data collected in Session 1B. For our 
primary analysis, we will use paired t-tests (α=0.0125 to account for multiple comparisons; 
using non-parametric methods if appropriate) to compare ρSW values for normal walking 

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trials with each exoskeleton condition. Secondary analyses with the same structure will be 
performed to investigate potential differences across trials in average stance and swing 
phase gluteus medius activity, and Rating of Perceived Stability. 
For Aim 2, all statistical comparisons will involve data collected in Session 2B. Each 
perturbation type will be analyzed separately. For speed and vision perturbations, we will 
use paired t-tests (α=0.025 to account for multiple comparison) to compare ρSW values 
between the zero impedance condition and each exoskeleton assistance condition. 
Secondarily, we will perform the same analyses with stance and swing phase gluteus 
medius activity and Rating of Perceived Stability. For mediolateral pull perturbations, we 
will perform an analysis with the same structure to compare the changes in mediolateral 
foot placement (relative to unperturbed steps). 
The sample size is based on a power analysis using data from previous studies in our lab, 
which revealed an effect size of assistance of 0.9.14 For Aim 1, with an alpha value of 
0.0125, the sample size of 21 will provide 90% power. For Aim 2, with an alpha value of 
0.025, a sample size of 18 (in case of dropout) will provide 90% power. 
Steps will be taken to minimize the risk of loss of confidentiality. Participants will be 
assigned a code, and all collected study data will be associated with this code, not with the 
participant's identity. The only links between participant code and identity will be in a 
study binder stored in a locked filing cabinet and an electronic enrollment document stored 
on a password protected server. All published data will be de-identified, and will not 
include any identifiable data. All data will be stored on a password-protected secure server 
that is backed-up nightly.  
The RESTORE registry (Pro#00037803), from which this study will recruit subjects, also 
serves as a data analysis tool by which interdisciplinary teams may share data across 
projects and provide MUSC’s stroke recovery research community with a more complete 
registry with key stroke elements. Some subjects may have participated or will participate 
in other stroke related research studies at MUSC. Sharing data from this and other stroke 
research studies with RESTORE will allow for more targeted recruitment efforts in the 
future and could reduce the burden placed on subjects by reducing the duplicative efforts 
of collecting common data and physical function assessments requested by multiple studies 
and storing them in one centralized and secure location.   
Subjects are informed in the consent process if they enroll into the RESTORE registry, 
their data from this study will be shared. Subjects will be asked to sign an authorization 
stating their health information may be disclosed to MUSC investigators requiring their 
data for their research projects upon approval by an Institutional Review Board.   
 
11.0 Provisions to Monitor the Data to Ensure the Safety of Subjects 
The study PI will be responsible for reviewing the collected data on a weekly basis to 
ensure data quality. All negative health events will be reported to the PI within one day of 
occurrence, for determination whether they qualify as adverse events. 
Any adverse events will be recorded, monitored, and promptly reported to the IRB, 
following policy HRPP 4.7. Our exclusion criteria will minimize the risk of enrolling 
participants with severe cardiovascular risk. Scheduled rest breaks will be provided 
between trials during experimental testing, as well as whenever requested. Minimization of 

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risk of adverse events will be accomplished by monitoring vital signs during trials in which 
subjects are performing potentially demanding exercise.  
 
12.0 Withdrawal of Subjects 
Participants will be withdrawn from the study without their consent if study staff determine 
that the participants are at risk of negative health events (e.g., large change in blood 
pressure from the initial screening assessment; consistent inability to maintain balance 
while walking on the treadmill). If a participant voluntarily withdraws from the study, their 
results will not be included in our data analysis, as our sample size accounts for anticipated 
dropout. 
 
13.0 Risks to Subjects 
Potential risks for participation in this study are low. Participants will wear an exoskeleton 
that can exert moderate sideways forces on their legs while walking. The exoskeleton has 
both software and hard mechanical stops that prevent the device from approaching the ends 
of the physiological range of motion. This device has been safely used to influence step 
width while walking with no negative effects.15 In some trials, participants will be 
mechanically perturbed while performing walking trials, thus creating the risk of a loss of 
balance. To mitigate the risk of possible negative effects of a loss of balance, participants 
will wear a safety harness attached to an overhead rail. The harness is designed to 
eliminate the consequences of falling as the device “catches” the subject should they trip or 
stumble. Additionally, in all walking trials, an investigator will be near the participant to 
provide assistance in the event of a loss of balance. To this point, over 100 people with 
chronic stroke (and many more neurologically-intact adults) have participated in studies 
investigating the effects of our perturbation devices. No adverse events related to the 
participants’ interaction with these devices have occurred. 
There is also the risk of minor muscle soreness due to the exercise of walking. This risk 
will be mitigated by walking only at speeds that are comfortable for each participant, and 
allowing rest breaks if participants ever indicate they are fatigued.  
General post-stroke function will be assessed using several commonly-used clinical tests. 
There is a risk of a loss of balance during the Functional Gait Assessment, in which 
individuals perform various functional gait tasks. We will mitigate this risk by having a 
trained clinician always next to participants, as is common in a clinical context. The other 
clinical tests either involve verbal questions or are of minimal physical risk.  
All research studies have the risk of loss of participant confidentiality. Our Data 
Management Plan (see above) will minimize this risk.  
 
14.0 Potential Benefits to Subjects or Others 
We do not anticipate any direct benefit to participants in this study. However, we anticipate 
that the results of this study will contribute to the development of an assistive device with 
the potential to improve the functional mobility and quality of life of future users with 
chronic stroke. As the risks to participants are low, we believe that the risks are reasonable 
with respect to the anticipated future benefits.  

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15.0 Sharing of Results with Subjects 
Research will be in the form of research data, and will not be shared with participants or 
others while the study is ongoing. Once the study is completed, de-identified data will be 
shared with the scientific community and study participants.  
 
16.0 Drugs or Devices  
This study involves a non-invasive exoskeleton that was developed at North Carolina State 
University, in collaboration with this study’s PI (Dean). This device has two degrees of 
freedom at the hip, allowing passive motion for hip flexion/extension while applying joint 
torques in the hip abduction/adduction direction.15 The peak hip torque that can be 
produced is 57 Nm, approximately half of the average torque that can be produced 
voluntarily by neurologically-intact individuals,16 and thus does not risk producing 
excessively large joint torques. The torques are generated using admittance control, which 
prevents rapid torque fluctuations that may be destabilizing. The device interfaces with 
participants through cloth straps designed for comfort. The device itself is attached to an 
overhead rail, which would support the weight of the device in case the user experiences a 
loss of balance. This device has been approved by the North Carolina State University 
Institutional Review Board, and was deemed to be a Nonsignificant Risk Device. This 
study also involves a non-invasive perturbation device used to apply mediolateral pulls to 
participants while they walk on a treadmill, which was developed by this study’s site PI 
(Dean).the perturbation device has been judged by the MUSC IRB to meet the criteria for a 
Nonsignificant Risk Device (as in the protocols Pro00062108, Pro00101810). 
 
References 
 
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