Proprioceptive Error Correction Technique Development to Promote Post-stroke Upper Limbs Motor Rehabilitation
Phase: NA
Conditions: Ischemic Stroke, Proprioception
Sponsor: Sungkyunkwan University

Cover Page or ClinicalTrial.gov
Documnet:
study protocol and Statistical Analysis Plan
Official Study Title:
Proprioceptive error correction technique development to promote 
post-stroke upper limbs motor rehabilitation.
NCT number:
not yes assigned
Principle Investigator
Hankyu Park, Ph.D.
AssociateProfessor,SungkyunkwanUniversity
DepartmentofBiomedicalEngineering
Co-Investigators
YoungdeokKim, M.S. (SungkyunkwanUniversity)
JunseungLee, M.S. (MetabioHealth/SungkyunkwanUniversity)
DukyongKim, Ph.D. (YonseiUniversity,RehabilitationMedicine)
JongwonLee, Ph.D. (YonseiUniversity,RehabilitationMedicine)
HyunheeLim, M.S. (YonseiUniversity,RehabilitationMedicine)
SeunghyunHan, M.S. (YonseiUniversity,RehabilitationMedicine)
Document date:
June 30, 2025

Study Protocol
Study 
Title
English
 Proprioceptive error correction technique development to promote post-stroke 
upper limbs motor rehabilitation
Investi
-
gator
Principal
Investigator
Affiliation
Position
Name
Field of study
contact information
Tel.
C.P
Sungkyunkwan 
University
Associate 
Professor
Hangue 
Park
Biomedical 
Engineering
+82-31-299-
4358
+82-10-9739-
9535
Co-Investi-
gators 
(Including 
Collaborating 
Institutions)
Sungkyunkwan 
University
Resear-
cher
Youngd
eok Kim
Interdisciplinary 
Program in 
Intelligent 
Precision 
Healthcare
-
+82-10-9072-
3483
Sungkyunkwan 
University
Resear-
cher
June 
Seung 
Lee
Metabio Health
-
+82-10-2087-
0016
Yonsei 
University
Professor
Deog 
Young 
Kim
Rehabilitation 
Medicine
-
-
Yonsei 
University
Resear-
cher
Jong 
Weon 
Lee
Rehabilitation 
Medicine
-
-
Yonsei 
University
Resear-
cher
Hyun 
Hee Lim
Rehabilitation 
Medicine
-
-
Yonsei 
University
Resear-
cher
Seung-
Hyeon 
Han
Rehabilitation 
Medicine
-
-
Planned study duration
June 2025 – May 2026 (1 year 0 months)
Study identifier
RS-2023-00209864
□Study Purpose and Background
- Purpose of the Study: The purpose of this study is to develop sensory transformation and 
augmentation techniques that minimize the effects of proprioceptive errors, with the goal of 
significantly improving motor learning and rehabilitation of the upper limbs. This study will 
evaluate the efficacy of the proprioceptive error correction techniques in individuals who have 
experienced a stroke.
- Rationale for the Study: Upper limb motor control is critical for stroke survivors to maintain 
independence in daily activities. The upper limbs are responsible for essential functions such as 
eating, dressing and undressing, body protection, hygiene management, and interaction with 
external objects. Therefore, it is important to investigate whether proprioceptive correction 
techniques can contribute to improved upper limb rehabilitation outcomes in this population.
- Scientific Background and Justification: The human nervous system often processes conflicting 
information from visual and proprioceptive inputs during upper limb control, which limits the 
effectiveness of motor learning. Real-time sensory feedback, a crucial component for motor 
learning, is often unreliable due to this sensory conflict. This study aims to address this issue 

by delivering supplementary information via electrical stimulation to resolve sensory conflicts 
and thereby enhance motor rehabilitation outcomes (refer to Figure 1).
<Figure 1. Schematic diagram of proprioceptive error correction technology>
□ Expected Study Duration
- From the approval date until May 2026, approximately 12 months (1 year) is anticipated for 
study completion.
□ Research Methods
- Overview of Research Methods
1) Development of Visual-Tactile Transformation Method:
The study aims to develop a method for delivering intuitive angular information of the elbow 
using non-invasive electrical stimulation and to determine the optimal stimulation parameters 
(including electrode placement, frequency, and intensity).
1-1) Determination of Electrode Placement:
Electrodes will be placed on the cubital fossa, the most sensitive hollow area on the inside of 
the elbow [1]. Starting from this reference electrode position (see Figure 2), slight adjustments 
will be made based on participant feedback to identify the optimal electrode placement that 
produces a clear electrical tactile sensation at the target site (elbow).

<Figure 2. Schematic illustration of electrode placement on the upper limb (elbow)>
1-2) Setting of Stimulation Frequency and Voltage Intensity
The range of stimulation frequencies and voltage intensities that evoke pulsing (flutter) and buzzing 
(electrical buzzing) sensations was determined. As reported in previous studies, the range for 
pulsing sensations in terms of stimulation frequency and voltage intensity has been established (see 
Figure 3). Specifically, the voltage intensity range was set between the minimum voltage at which 
each participant began to perceive the stimulation (V_min) and the maximum voltage at which 
discomfort was first reported (V_max). The frequency range was set from 10 Hz to 70 Hz, the 
typical upper limit at which participants can distinguish the stimulation.
Based on these criteria, the stimulation frequency and intensity ranges for each sensation were 
determined. In prior studies conducted by our research group, the maximum tolerable voltage 
(V_max) at which discomfort was reported ranged from approximately 10 to 22 V for both male and 
female participants [3, 4, 5, 6] (see Figure 3). Generally, females exhibit slightly lower V_max values 
than males (by approximately 0 to 5 V), which is attributed to thinner skin and muscle tissue in 
females [7].
It is noteworthy that the maximum voltage levels observed for both males and females correspond 
to approximately 30–70% of the safety voltage standards set by the Occupational Safety and Health 
Administration. During experiments, electrical stimulation is administered at voltage levels below 
the participant’s discomfort threshold (V_max) to ensure safety and comfort.
<Figure 3. Example ranges of electrical stimulation intensity (left) and frequency (right) for 
individual participants.>
1-3) Measurement of Elbow Angle and Determination of Angle-to-Tactile Conversion Formula
The elbow angle is measured using a variable resistor (RV09H-20SQ, 50 kΩ). A goniometer 
marked in 1-degree increments from 0° to 150° is placed on the inner and outer surfaces of a 
box, aligned with the flexion and extension directions of the elbow joint. Velcro straps are used 
to secure the participant’s upper limb to the inner goniometer, fixing the elbow joint and the 
distal radius and ulna in place. As the participant moves their arm, the inner goniometer moves 
accordingly, allowing the current elbow angle to be measured. A pointer is attached to the outer 
goniometer to enable the participant to indicate the angle. To ensure that the participant cannot 

see their moving limb, the inner and outer goniometers are enclosed within a box of suitable 
size, as illustrated in <Figure 4>.
The resistance value measured via the variable resistor is converted into the corresponding 
elbow angle. Based on the measured elbow angle, the electrical stimulation frequency is adjusted 
accordingly for the experiment. The conversion formula for mapping elbow angle to electrical 
stimulation frequency is as follows:

max 
max min
min
≤≤max

min
min max 
min
min ≤≤
 
denotes the target angle to be learned, which is set differently depending on the 
experimental condition. maxand minare defined as °, °, respectively. maxand 
minare set to 70 Hz and 10 Hz, respectively. represents the current elbow angle, and 
denotes the electrical stimulation frequency corresponding to the current elbow angle.
<Figure 4. Box-Type Elbow Angle Measurement Device>
2) Methods
2-1) Study Period
The total study duration spans a minimum of three weeks. For each of the three experimental 
conditions, assessments are conducted during Visit 1 and Visit 2, with a washout period of at 
least 7 days between conditions.
2-2) Randomization and Procedure
All participants enrolled in the study are assigned a random number generated using Python. 
Based on a pre-defined randomization protocol, each participant is randomly allocated to a 
specific sequence of the three experimental conditions: Electrical Stimulation Cue, Visual Cue, 
and No Cue.

2-3) Visit Schedule
All participants receive standard therapy in accordance with clinical guidelines for stroke 
rehabilitation. The study intervention is provided in addition to standard therapy. A total of six 
visits are planned. During the screening visit, participants (or their legal representatives) provide 
written informed consent. The participant’s medical history and current clinical status are 
reviewed to confirm eligibility. Eligible participants are then assigned a randomization number 
and allocated to a randomized order of the three cueing conditions: Electrical Stimulation Cue, 
Visual Cue, and No Cue.
Baseline assessments are conducted at Visit 1, Visit 3, and Visit 5—prior to the start of each 
intervention. After the baseline assessment, one session of the corresponding intervention is 
administered. Following each intervention session, additional efficacy assessments are performed 
during all visits. A washout period of at least 7 days is maintained between each experimental 
condition.
The overall study flow is summarized in Figure 5.
<Figure 5. Study Protocol Flowchart>
2-4) Experimental Intervention Protocols
2-4-1) Electrical Stimulation Cue Protocol
The intervention is administered once for 30 minutes. An electrical stimulation device developed 
by the research team is attached to the participant’s cubital fossa. Stimulation is provided with 
increasing frequency, reaching a maximum of 70 Hz as the elbow joint approaches a pre-defined 
target angle. This target angle is individually set within the participant’s available range of 
motion based on baseline assessments. During the session, the participant attempts to match 
their elbow angle to the target angle while receiving verbal feedback from the examiner.
2-4-2) Visual Cue Protocol
The intervention is administered once for 30 minutes. A visual cue displays the difference 
between the current elbow joint angle and a predefined target angle on a screen. The target 
angle is individually set within each participant’s range of motion based on baseline assessments. 
The participant is instructed to match their elbow angle to the target angle while receiving 
verbal feedback from the examiner.
2-4-3) No Cue Protocol
The intervention is administered once for 30 minutes. The participant attempts to match their 
elbow joint angle to a verbally instructed target angle, relying solely on verbal feedback from 
the examiner.

2-5) Outcome Measures and Assessment Procedures
2-5-1) Threshold Detection
An angle-detecting sensor developed by the research team (see Section 1-3) is attached to the 
participant’s affected elbow joint. The examiner holds the medial and lateral epicondyles of the 
participant’s affected upper limb with one hand and the distal radius and ulna with the other. 
The test is conducted four times in total: two trials in the flexion direction and two in the 
extension direction, in random order. Each trial starts from 60° of elbow flexion. The examiner 
moves the joint at approximately 6° per second, and the participant is instructed to verbally 
report when they perceive joint movement. If the participant does not respond before the joint 
reaches 30° of motion, a score of 0 is recorded.
-2 points: Participant perceives movement of the elbow joint.
-0 points: Participant does not perceive movement of the elbow joint.
2-5-2) Joint Position Reproduction
An angle-detecting sensor developed by the research team is attached to both of the 
participant’s elbow joints. The examiner holds the medial and lateral epicondyles of the 
participant’s affected upper limb with one hand and the distal radius and ulna with the other. 
The examiner passively moves the affected arm to one of 12 pre-defined flexion or extension 
angles in the following order: 60°, 90°, 30°, 120°, 60°, 30°, 90°, 120°, 30°, 60°, 120°, and 90°. After 
each presentation, the participant is asked to reproduce the same angle using the unaffected 
limb. The average difference between the target angles and the reproduced angles across the 12 
trials is calculated and used for analysis.
2-5-3) position Sense Test 
Apparatus
Goniometers marked in 1-degree increments from 0° to 120° are installed on the inner and outer 
surfaces of a box aligned with the elbow joint's flexion and extension axis. Velcro straps are 
used to secure the participant’s upper limb and distal radius and ulna in place. A pointer is 
attached to the outer goniometer to allow the participant to indicate the perceived angle. A box 
of appropriate size is placed between the inner and outer surfaces to block the participant’s 
view of their own arm during the test.
※ The apparatus was newly designed with reference to the Wrist Position Sense Test Apparatus 
(see Figures 4 and 6).

<그림 6. Wrist position sense test apparatus>
Procedure
The examiner passively moves the participant’s upper limb to one of 12 predefined elbow flexion 
or extension angles in the following order: 60°, 90°, 30°, 120°, 60°, 30°, 90°, 120°, 30°, 60°, 120°, 
and 90°. The examiner attempts to maintain a consistent speed during both flexion and 
extension movements. After the target angle is reached, the participant uses their contralateral 
(unaffected) hand to indicate the perceived angle by adjusting a pointer on the outer goniometer 
of the device. The absolute differences between the presented and indicated angles are recorded 
for each of the 12 trials, and the average error is calculated for analysis.
2-5-4) Motor & Position Sense Test 
Apparatus
Goniometers marked in 1-degree increments from 0° to 120° are installed on both the inner and 
outer surfaces of a box aligned with the flexion and extension axis of the elbow joint. Velcro 
straps are used to secure the participant’s upper limb, including the elbow joint and distal 
radius and ulna. A pointer is attached to the outer goniometer to allow participants to indicate 
perceived joint angles. A box of appropriate size is placed between the inner and outer 
goniometers to ensure that the participant’s tested arm remains out of view during the 
assessment.

Procedure
After assessing the participant’s upper limb range of motion (ROM), the examiner manually 
moves the goniometer pointer to present 12 different target angles within the participant’s 
available ROM. The participant is instructed to actively move their elbow joint to match the 
presented angle by flexing or extending the joint. During each trial, the participant is 
encouraged to move at a consistent speed. After the examiner presents the target angle using 
the pointer, the participant moves their limb to the angle they perceive as matching the target. 
The difference between the presented and perceived angles is recorded for each of the 12 trials, 
and the average error is calculated for analysis.
2-5-5) Fugl-Meyer Assessment (FMA): Upper Limb Position Sense Test
The examiner evaluates proprioception in the affected upper limb in the following order: 
shoulder joint, elbow joint, wrist joint, and thumb. Each joint is tested at least four times within 
the participant’s available ROM. All assessments are conducted with the participant's eyes 
closed.
For the shoulder and elbow joints, the examiner holds the participant’s medial and lateral 
epicondyles with one hand and the distal radius and ulna with the other. The examiner 
randomly moves the joint up or down in flexion/extension directions at least four times to 
evaluate position sense.
For the wrist joint, the examiner holds the distal radius and ulna with one hand and the heads 
of the second and fifth metacarpals with the other hand, then passively moves the wrist joint up 
or down in random order.
For the thumb, the examiner holds the interphalangeal joint with one hand and the lateral 
aspects of the distal phalanx with the other, passively moving the thumb up or down at least 
four times in random order.
Light touch testing is conducted using the tip of a cotton swab on each joint of the affected 
limb.
-2 points: Accurately perceives joint position.
-1 point: Inconsistent perception, but correctly identifies at least 3 out of 4 trials.
-0 points: Unable to perceive joint position.
2-5-6) Sensory Testing (Including Monofilament Sensory Test)
The examiner performs sensory testing on the shoulder, elbow, wrist, and thumb joints of the 
affected upper limb. All tests are conducted with the participant’s eyes closed.
Sharp/Blunt Discrimination: A paperclip is used to deliver sharp and blunt stimuli, applied five 
times per joint. The number of correct responses out of five is recorded.
Temperature Sensation: Glass tubes filled with cold and warm water are used to assess thermal 
sensation. Each joint is tested five times, and the number of correct responses is recorded.
Monofilament Sensory Test: A 10g (5.07 Semmes-Weinstein) monofilament is applied 
perpendicularly to each joint until the monofilament bends. The participant is asked to report 
whether they feel the sensation of contact. This test is performed on each joint individually.

2-5-7) Box and Block Test: BBT
The Box and Block Test (BBT) is used to assess gross manual dexterity and agility of the upper 
limb, evaluating both the dominant and non-dominant hands. Participants are seated upright at 
a table approximately 65 cm in height, with the testing apparatus centered in front of them. A 
total of 150 wooden cubes measuring approximately 2.5 cm³ are initially placed on the side 
corresponding to the dominant hand. The participant is instructed to pick up one block at a 
time and transfer it over a 15.2 cm-high partition into the opposite compartment. The number 
of blocks successfully transferred within 60 seconds is recorded. The same procedure is 
repeated for the non-dominant hand. Assessments are conducted under two conditions: with 
eyes open and eyes closed.
2-5-8) Action Research Arm Test: ARAT
The Action Research Arm Test (ARAT) evaluates upper limb function across 19 items divided 
into 4 domains, with a total possible score ranging from 0 to 57 points. Items within each 
domain must be administered in order. If the participant successfully completes the first item in 
a domain, the domain is scored as full points, and the test proceeds to the next domain. If the 
first and second items in a domain are not performed successfully, the domain is scored as 
zero and the test advances to the next domain. The domains and their corresponding items are 
detailed below.
Grasp
① Pick up a 10cm, block, wood cube
② Pick up a 2.5cm, block, wood cube
③ Pick up a 5cm, block, wood cube
④ Pick up a 7.5cm, block, wood cube
⑤ Pick up a 7.5cm diameter, cricket ball
⑥ Pick up a 10 x 2.5 x 1cm stone 
Grip
① Pour water from glass to glass
② Insert 2.25cm tube
③ Insert 1 x 16cm tube
④ Washer (3.5cm diameter) over bolt
Pinch
① Pick up a 6mm ball bearing with 3rdfingerandthumb
② Pick up a 1.5cm marble with index finger and thumb
③ Pick up a 6mm ball bearing with 2ndfingerandthumb
④ Pick up a 6mm ball bearing with index finger and thumb
⑤ Pick up a 1.5cm marble with 3rdfingerandthumb
⑥ Pick up a 1.5cm marble with 2ndfingerandthumb

Gross movement
① Place hand behind head
② Place hand on top of head
③ Place hand to mouth
-3 points: Movement is performed normally within 5 seconds.
-2 points: Movement is completed but abnormally slow, taking between 5 and 60 seconds.
-1 point: Movement is partially performed within 60 seconds.
-0 points: No movement or unable to perform within 60 seconds.
3) Participant Selection and Exclusion Criteria
3-1) Inclusion Criteria: Participants meeting all of the following criteria will be included
①Patients diagnosed with ischemic or hemorrhagic stroke.
②Stroke confirmed by CT or MRI imaging.
③Presence of proprioceptive sensory impairment associated with stroke.
④Chronic phase stroke patients, at least 3 months post-stroke onset.
⑤Ability to voluntarily flex and extend the elbow joint.
⑥Age 19 years or older.
⑦Written 
informed 
consent 
provided voluntarily 
by the participant or 
their legal 
representative.
3-2) Exclusion Criteria: Participants meeting any of the following criteria will be excluded
①K-MMSE score < 10 or severe aphasia making communication difficult.
②Severe pain during elbow joint movement.
③Presence of elbow joint contracture, spasticity, ataxia, musculoskeletal disorders, fractures
unhealed ulcers, or open wounds.
④Progressive or unstable stroke condition.
⑤Presence of unilateral neglect.
⑥Coexisting significant neurogenic disorders.
⑦Presence of major psychiatric disorders such as major depressive disorder, schizophrenia
bipolar disorder, or dementia.
⑧Presence of a pacemaker.
4) Recruitment and Management of Study Participants
Ten chronic stroke patients with proprioceptive sensory impairment will be recruited. Recruitment 
will be conducted among inpatients at Yonsei Severance Hospital. Participants and their legal 
representatives will be provided with an explanation by a physician or research staff regarding the 
study details outlined below under ‘Experimental Procedures’ and will make an informed decision 
regarding participation.
4-1) Explanation of the Experimental Procedure
This experiment is conducted with the purpose of enabling participants to perceive the position 
of the arm by delivering information about the elbow joint angle through electrical stimulation. 

Electrical stimulation refers to the application of current through electrodes attached to the 
skin, using a voltage supply device with current limitations. The applied voltage and current 
levels comply with safety standards set by the Korea Occupational Safety and Health Agency and 
the Ministry of Food and Drug Safety, specifically “voltages not exceeding 30 V and currents not 
exceeding 50 mA,” which are considered safe for human exposure.
The intensity of the electrical stimulation used in this study is comparable to or lower than that 
of low-frequency massage commonly employed in orthopedic physical therapy (refer to Section 
7-3-3 of this document). Previous studies by our research team, which targeted sensitive regions 
of the hand, reported that the voltage level at which participants began to feel discomfort 
(V_max) ranged from approximately 10 to 22 V in both males and females. Generally, females 
exhibit slightly lower V_max values than males, attributed to thinner skin and muscle mass. 
These maximum voltage levels correspond to approximately 30–70% of the safety voltage 
standard of 30 V established by the Korea Occupational Safety and Health Agency for both 
sexes. During the experiment, electrical stimulation will be applied at intensities below the 
participant’s discomfort threshold (V_max). Furthermore, the maximum current will be restricted 
to 20% (10 mA) of the safety current standard.
All participants will receive treatment according to standard clinical guidelines for stroke, with 
the experimental intervention provided in addition to standard care. The voltage of electrical 
stimulation will be gradually increased from 0 V in increments of 0.1 V. If a participant reports 
any discomfort, the stimulation will be immediately discontinued. Electrical stimulation will be 
preceded by a cue to inform the participant that stimulation is about to be applied. Stimulation 
will be delivered to the affected side’s cubital fossa. For participant safety, the investigator will 
continuously monitor for any abnormal arm movement or reported discomfort throughout the 
experiment. Participants may terminate the experiment at any time according to their own will.
4-2) Pre-experiment Procedures
Prior to participation, subjects will complete a pre-experiment questionnaire to confirm informed 
consent and eligibility for participation. Responses, including personal information and consent 
forms, will be securely stored.
4-3) Procedures on the Day of the Experiment
Immediately before the experiment, participants will complete a brief questionnaire assessing 
their sleep duration from the previous night and current physical condition to evaluate 
readiness for the session. Potential risks will be verbally explained. Participants will be informed 
that they may withdraw from the study at any point during the procedure for any reason. If 
severe discomfort arises from the electrical stimulation, the experiment will be terminated 
immediately.
4-4) Post-experiment Monitoring
Participants will be monitored through questionnaires administered 3 and 7 days after the 
experiment to assess any adverse effects such as skin allergic reactions or arm discomfort. 
Safety will be further verified by comparing these responses to those collected prior to the 

experiment (Section 4-2).
4-5) Justification for Target Sample Size
This study is a preliminary investigation involving stroke patients, designed to evaluate the 
feasibility of the study protocol and to estimate effect sizes of key outcome variables. 
Accordingly, an initial sample size of 10 participants will be recruited. Given the exploratory 
nature of this pilot study, a limited sample is appropriate for assessing the suitability of the 
study design, reliability of measurement instruments, and feasibility of procedures. The chosen 
sample size is consistent with the scale of similar preliminary studies and takes into 
consideration both the exploratory aims and practical feasibility of the research. The data 
obtained will provide foundational information necessary for designing future studies and 
calculating appropriate sample sizes.
5) Study Procedures 
5-1) Recruitment and Screening of Clinical Research Participants
Stroke patients admitted to or receiving outpatient treatment at the Department of Rehabilitation 
Medicine, Severance Hospital, located in Seodaemun-gu, Seoul, will be recruited. After providing 
an explanation of the study in a private setting, sufficient time will be allowed for participants 
and their legal guardians to review the information. Written informed consent will be obtained 
only from those who agree to participate.
Screening will be conducted exclusively for participants who have provided written consent. The 
screening process will include a review of medical records, interviews, manual physical 
examination, and the administration of the Korean Mini-Mental State Examination (K-MMSE) by 
the investigator to determine eligibility. Participants deemed eligible will be formally enrolled in 
the study; those who do not meet inclusion criteria will not be enrolled.
5-2) Experimental Site
The evaluation and intervention for this study will take place in the Brain Stimulation Treatment 
Room on the 6th floor of Severance Rehabilitation Hospital, where the electrical stimulation 
platform is installed.
5-3) Roles of Collaborative Research Institutions
The Integrated Neuroprosthetics Laboratory at Sungkyunkwan University is responsible for the 
development, maintenance, and servicing of the electrical stimulation platform used for the 
intervention.
The Severance Institute for Rehabilitation Medicine is responsible for participant recruitment, 
clinical intervention, and assessment. The institute consists of one Rehabilitation Medicine 
professor (principal investigator), one specialist (researcher), and one therapist (researcher). The 
principal investigator oversees appropriate participant selection and conducts weekly inspections 
of equipment such as electrical stimulators and electrode patches to prevent accidents. The 
investigator also has the authority to immediately terminate the experiment if any safety 
concerns arise during the procedure.

6) Interview Items, Analysis Methods, and Interview Tools 
[Post-experiment Questionnaire Items]  
1. Did you experience any discomfort in your arm or wrist due to the band, electrodes, or other 
setup during the experiment?
Not at all                          Moderately                             Extremely
 1                  2                   3                   4              5 or more 
2. Did the electrical stimulation help you in perceiving or controlling the angle of your elbow 
during the experiment?
Not at all                          Moderately                             Extremely
 1                  2                   3                   4              5 or more    
              
3. Did you find the electrical stimulation uncomfortable during the experiment?
Not at all                          Moderately                             Extremely
 1                  2                   3                   4              5 or more    
4. Did you perceive the electrical stimulation clearly during the experiment?
Not at all                          Moderately                             Extremely
 1                  2                   3                   4              5 or more 
5. Did you pay attention to the information delivered via the electrical stimulation during the 
experiment?
Not at all                          Moderately                             Extremely
 1                  2                   3                   4              5 or more  
6. Please freely provide any suggestions or comments regarding the experimental procedure, 
equipment, or other related aspects.
7)  Criteria and Methods for Participant Safety Evaluation
7-1) Continuous Monitoring of Skin Allergic Reactions
Gel-type electrodes attached to the skin may cause mild allergic reactions. These reactions will 
be objectively assessed through visual inspection by the experimenter and a questionnaire based 
on a Likert scale. If any noticeable allergic reactions are observed or the participant reports any 
such reactions, the experiment will be immediately terminated.
7-2) Continuous Monitoring of Participant Discomfort
Electrical stimulation applied to the skin may cause mild discomfort. Discomfort levels will be 
objectively assessed using a Likert scale-based questionnaire, and continuously monitored 
through verbal reports from participants.
7-3) Safety Verification of the Electrical Stimulator Used in the Experiment
7-3-1) Safety and Performance Evaluation Guidelines for Personal Electrical Stimulators
The safety of the stimulation intensity is ensured based on the Guidelines for Safety and 
Performance Evaluation of Personal Electrical Stimulators published by the Ministry of Food and 
Drug Safety (MFDS) [2], specifically referring to Table 7: Current Limits. According to the 
guideline, the maximum stimulation frequency is 400 Hz, and the current limit is 50 mA. The 
stimulation parameters used in the experiment will be set well within these safety thresholds.
7-3-2) Electrical Stimulator Settings Used in the Experiment
The electrical stimulator used in this study is configured to ensure that both voltage and 
current remain below predefined maximum safety limits. This stimulator has previously received 

IRB approval more than 10 times each in the United States and Korea, and has been employed 
in over 20 peer-reviewed publications over the past 10 years [3, 4, 5, 6, 10, 11].
-Frequency Setting: The stimulation frequency is capped at 100 Hz, which corresponds to less 
than 25% of the maximum allowable frequency (400 Hz) specified by regulatory guidelines.
-Current Setting: Based on a maximum stimulation voltage of 30V and an average skin 
impedance 
of 
10k, 
the 
theoretical 
maximum 
current 
is 
approximately 
3mA. 
Empirical 
measurements using electrodes attached to human skin confirmed a stimulation current between 
2–4mA, which is below 8% of the regulatory current limit of 50mA according to the safety and 
performance evaluation guidelines for personal electrical stimulators. Furthermore, an additional 
safety limit is imposed at 10mA, representing 20% of the allowable limit.
According to the Korea Occupational Safety and Health Agency’s guidelines on electrical hazards 
and electrocution prevention [12], currents around ~1mA are referred to as the ‘minimum 
perceptible current’ and cause only mild sensation, while pain typically occurs at ~15mA. Thus, 
even at the maximum current level set in this study, no pain is expected.
-Voltage Setting: The maximum stimulation voltage is restricted to 30 V. According to safety 
guidelines from the Korea Occupational Safety and Health Agency [13], voltages of 30V or below 
are considered safe and non-hazardous even under worst-case scenarios, such as low skin 
impedance. This ensures that the participant's safety is preserved even in the event of unusual 
physiological conditions.
7-3-3) List of Studies Using Electrical Stimulators with the Same Specifications as the One Used 
in This Experiment
To account for the physical characteristics of the study participants, reference data obtained 
from East Asian populations have been incorporated into this research [18], [19], [20], [21], [22], 
[23], [24]. This inclusion reflects a consideration that East Asians may differ from Western 
populations in terms of skin thickness and sensitivity.
The following is a list of previous studies that utilized electrical stimulators with specifications 
equivalent to the device used in this experiment:
7-3-3-1) [3] (International): Used electrical stimulation to convey the point of contact of a ball 
on a VR table tennis paddle.
7-3-3-2) [14] (International): Delivered postural sway information via electrical stimulation while 
standing on a balance board.
7-3-3-3) [15] (International): Applied electrical stimulation to the tongue for haptic feedback 
purposes.
7-3-3-4) [16] (International): Employed electrical stimulation to modulate elbow joint angles.
7-3-3-5) [17] (International): Used electrical stimulation to control the angles of the index finger 
and thumb.
7-3-3-6) [18] (Korea): Investigated the effects of EMS frequency on performance in a visual 
stimulus-response task.
7-3-3-7) [19] (Korea): Designed and evaluated a dry e-tactile electrode EMS brace for elite 
badminton players with knee pain.
7-3-3-8) [20] (Korea): Developed injury-prevention socks integrating EMS and stretch sensors for 

home training.
7-3-3-9) [21] (Japan): Studied the early application of EMS to prevent muscle atrophy and 
weakness after ACL reconstruction.
7-3-3-10) [22] (Japan): Developed a gravity-free training method combining voluntary muscle 
contractions with electrical stimulation.
7-3-3-11) [23] (China): Created an electric muscle simulator based on functional electrical 
stimulation (FES).
7-3-3-12) [24] (China): Applied electrical stimulation therapy to treat peripheral nerve injuries.
7-3-3-13) Studies [18], [19], and [20] were conducted on Korean participants.
7-3-3-14) Studies [21] and [22] were conducted on Japanese participants.
7-3-3-15) Studies [23] and [24] were conducted on Chinese participants.
7-3-4) Commercial Personal Electrical Stimulators
The electrical stimulator used in this study operates with lower current and frequency levels 
compared to specifications of commonly available commercial personal electrical stimulation 
devices:
-The EMS 1000 (Hyundai Bio Medical Co., Ltd., Seoul, Republic of Korea) specifies a maximum 
output current of 17 mA and a maximum frequency of 200 Hz.
-The EMGFES 1000 (Cypermedic Co., Ltd., Gwangju, Republic of Korea) specifies a maximum 
output current of 99 mA and a maximum frequency of 200 Hz.
-The KD-PRO-5000 Gold (Kukdong Electronics Co., Ltd., Incheon, Republic of Korea) specifies a 
maximum output current of 12.2 mA and a maximum frequency of 1,190 Hz.
-The SERA (GOS Co., Ltd., Gyeongsan, Republic of Korea), a personal rehabilitation walking 
assist device, specifies a maximum output current of 80 mA and a maximum frequency of 120 
Hz.
8) Subject Withdrawal Criteria
8-1) Subjects who exhibit visually identifiable allergic skin reactions upon attachment of the 
gel-type electrodes, or who report discomfort greater than or equal to 3 on a Likert scale, will 
be excluded from the study.
8-2) Subjects who consistently report discomfort due to electrical stimulation will also be 
excluded.
First, stimulation intensity is set significantly lower than the discomfort-inducing threshold to 
prevent such issues.
Second, if a subject verbally reports discomfort during the experiment, the procedure will be 
immediately paused.
After a rest period of approximately 3–5 minutes, the experiment may be resumed.
If discomfort persists upon resumption, the subject will be withdrawn from the study.
9) Research Timeline
Subject recruitment and experimental procedures are scheduled to begin after July 1, 2025.

The study aims to complete experiments with 10 participants by August 31, 2027.
10) Participant Compensation
The electrical stimulation used in this study does not involve invasive therapy; therefore, no 
known or anticipated adverse effects are expected. However, participants may experience minor 
discomfort such as skin irritation or slight muscle contractions. In the event of any unexpected 
incidents during the experiment, the research staff will immediately notify the principal 
investigator, Professor Hankyu Park. If a clear causal relationship is established between the 
study and any injury, Professor Park will assume responsibility for compensation and treatment 
costs.
11) Informed Consent and Study Information Sheet
Please refer to the separately attached document titled “5. Informed Consent Form.”
12) Other Ethical Considerations for Research Conduct
All experimenters will thoroughly familiarize themselves with and strictly adhere to this protocol 
to ensure the ethical conduct of the research. The principal investigator, Professor Hankyu Park, 
will periodically assess whether the experimenters fully understand and comply with the protocol.
□ Expected Outcomes of the Study
Although sensory errors frequently occur after stroke, conventional motor rehabilitation relies 
mainly on repetitive training without addressing these sensory deficits, resulting in limited 
effectiveness. This study aims to improve the effectiveness of upper limb and finger motor 
rehabilitation by delivering proprioceptive information through tactile channels via electrical 
stimulation (proprioceptive error correction technology). By addressing sensory errors overlooked 
in traditional rehabilitation, this approach is expected to reduce patients’ frustration and fatigue 
during rehabilitation, thereby significantly enhancing their quality of life despite the time and 
effort required.
□ References
[1] Van Den Berg, A. A. "Skin sensitivity of the arm: A comparison of five sites." Anaesthesia 51.2 
(1996): 194-197.
[2] Ministry of Food and Drug Safety. Personal Electrical Stimulator Safety and Performance 
Evaluation Guidelines (Consumer Guide) [Internet]. 2014 [cited 2024 Sep 27]. Available from: 
https://www.mfds.go.kr/brd/m_1060/view.do?seq=12403&srchFr=&srchTo=&srchWord=&srchTp=&it
m_seq_1=0&itm_seq_2=0&multi_itm_seq=0&company_cd=&company_nm=&page=88
[3] Oh, S., Yoon, B. J., & Park, H. (2024). Location-based electrotactile feedback localizes hitting 
point in virtual-reality table tennis game. Biomedical Engineering Letters, 14: 593&#8211;604. 
https://doi.org/10.1007/s13534-024-00354-7
[4] Oh, S., Patton, J. L., & Park, H. (2022). Electro-prosthetic E-skin Successfully Delivers Elbow 
Joint Angle Information by Electro-prosthetic Proprioception (EPP). In 2022 44th Annual 
International 
Conference 
of 
the 
IEEE 
Engineering 
in 
Medicine 
& 
Biology 
Society 
(pp. 

1485&#8211;1488). https://doi.org/10.1109/EMBC48229.2022.9871002 
[5] Manoharan, S., Oh, S., Jiang, B., Patton, J. L., & Park, H. (2022). Electro-prosthetic E-skin 
Successfully Delivers Finger Aperture Distance by Electro-Prosthetic Proprioception (EPP). In 
2022 44th Annual International Conference of the IEEE Engineering in Medicine & Biology Society 
(pp. 4196&#8211;4199). https://doi.org/10.1109/EMBC48229.2022.9871592
[6] Zhao, Z., Yeo, M., Manoharan, S., Ryu, S. C., & Park, H. (2020). Electrically-evoked proximity 
sensation can enhance fine finger control in telerobotic pinch. Scientific reports, 10(1), 163. 
https://doi.org/10.1038/s41598-019-56985-9
[7] Mencel, J., Jaskolska, A., Marusiak, J., Kisiel-Sajewicz, K., Siemiatycka, M., Kaminski, L., & 
Jaskolski, A. (2021). Effect of gender, muscle type, and skinfold thickness on myometric 
parameters in young people. PeerJ, 9: e12367. https://doi.org/10.7717/peerj.12367
[8] Harris, M. L., et al. "Quadriceps muscle weakness following acute hemiplegic stroke." Clinical 
rehabilitation 15.3 (2001): 274-281
[9] Mann, Geraldine E., et al. "A pilot study to investigate the effects of electrical stimulation on 
recovery of hand function and sensation in subacute stroke patients." Neuromodulation: Technology 
at the Neural Interface 8.3 (2005): 193-202.
[10] Raghav Hari Krishna, V. S., Kim, J., Chang, S.-H., Choe, Y., & Park, H. (2024). Proportional 
sway-based electrotactile feedback improves lateral standing balance. Frontiers in Neuroscience, 
18: 1249783. https://doi.org/10.3389/fnins.2024.1249783 
[11] Jiang, B., Dollahon, D., Manoharan, S., Oh, S., Park, H., & Kim, J. (2023). Improving Tongue 
Command Accuracy: Unlocking the Power of Electrotactile Feedback Training. In 2023 45th Annual 
International Conference of the IEEE Engineering in Medicine & Biology Society (pp. 1&#8211;5). 
https://doi.org/10.1109/EMBC40787.2023.10340808 
[12] [12] Korea Occupational Safety & Health Agency. Safety Voltage (安全電壓, safety voltage). 2023 
Jul 
3 
[cited 
2024 
Sep 
27]. 
Available 
from: 
https://kosha.or.kr/kosha/data/terminologyDictionary.do?mode=view&articleNo=392985
[13] Korea Occupational Safety and Health Service. Safety Voltage (安全電壓, safety voltage). 2016 
Nov 
10 
[cited 
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Sep 
27]. 
URL: 
https://www.safety.or.kr/safety/bbs/BMSR00203/view.do?boardId=127877&menuNo=200088  
[14] Raghav Hari Krishna VS, Kim J, Chang S-H, Choe Y and Park H (2024) Proportional 
sway-based electrotactile feedback improves lateral standing balance. Front. Neurosci. 18:1249783. 
doi: 10.3389/fnins.2024.1249783
[15] B. Jiang, D. Dollahon, S. Manoharan, S. Oh, H. Park and J. Kim, "Improving Tongue Command 
Accuracy: Unlocking the Power of Electrotactile Feedback Training," 2023 45th Annual International 
Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), Sydney, Australia, 2023, 
pp. 
1-5, 
doi: 
10.1109/EMBC40787.2023.10340808. 
keywords: 
{Training;Neurological 
diseases;Visualization;Tongue;Machine 
learning 
algorithms;Assistive 
technologies;Electrical 
stimulation;Electrotactile feedback;electrical stimulation (E-stim);intra-oral assistive technology 
(AT);tongue motor learning;tongue command accuracy},
[16] S. Oh, J. L. Patton and H. Park, "Electro-prosthetic E-skin Successfully Delivers Elbow Joint 
Angle Information by Electro-prosthetic Proprioception (EPP)," 2022 44th Annual International 
Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), Glasgow, Scotland, 

United 
Kingdom, 
2022, 
pp. 
1485-1488, 
doi: 
10.1109/EMBC48229.2022.9871002. 
keywords: 
{Electrodes;Neurological diseases;Motor drives;Perturbation methods;Nervous system;Skin;Silicon},
[17] S. Manoharan, S. Oh, B. Jiang, J. L. Patton and H. Park, "Electro-prosthetic E-skin Successfully 
Delivers Finger Aperture Distance by Electro-Prosthetic Proprioception (EPP)," 2022 44th Annual 
International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), Glasgow, 
Scotland, United Kingdom, 2022, pp. 4196-4199, doi: 10.1109/EMBC48229.2022.9871592. keywords: 
{Wearable computers;Fingers;Apertures;Nervous system;Skin;Biology;Sensors},
[18] Kang M., Kim J., Kim K. (2024 Jan 24). The effect of frequency of electrical muscle stimulation 
on visual stimulus-response task performance. Proceedings of the Korean HCI Conference, 
Gangwon, Korea.
[19] Lee J., Park J., Kim J. (2023). Design and effect of a dry E-textile electrode EMS (Electric Muscle 
Stimulation) brace for elite badminton players with knee pain. Fashion Business, 27(5), 93-107.
[20] Song G. (2023). Development of ankle injury prevention socks using EMS and stretch sensors 
for home training [Master’s thesis, Soongsil University]. Soongsil University Graduate School, 
Seoul, Korea.
[21] S. Hasegawa, M. Kobayashi, R. Arai, A. Tamaki, T. Nakamura, and T. Moritani, "Effect of early 
implementation of electrical muscle stimulation to prevent muscle atrophy and weakness in patients 
after anterior cruciate ligament reconstruction," J. Electromyogr. Kinesiol., vol. 21, no. 4, pp. 
622-630, 2011, doi: 10.1016/j.jelekin.2011.01.005.
[22] K. Yoshimitsu, N. Shiba, H. Matsuse, Y. Takano, T. Matsugaki, T. Inada, Y. Tagawa, and K. 
Nagata, "Development of a training method for weightless environment using both electrical 
stimulation and voluntary muscle contraction," Tohoku J. Exp. Med., vol. 220, no. 1, pp. 83-93, Dec. 
2009, doi: 10.1620/tjem.220.83.
[23] H. Wang et al., "An electrical muscle simulator based on functional electrical stimulation," 2012 
IEEE International Conference on Robotics and Biomimetics (ROBIO), Guangzhou, China, 2012, pp. 
1906-1911, doi: 10.1109/ROBIO.2012.6491246.
[24] Ni L, Yao Z, Zhao Y, Zhang T, Wang J, Li S and Chen Z (2023) Electrical stimulation therapy 
for peripheral nerve injury. Front. Neurol. 14:1081458. doi: 10.3389/fneur.2023.1081458

   The principal investigator hereby submits the recent curriculum vitae and 
documentation of completed IRB training
June 30, 2025
                                       Principal Investigator:  Hankyu Park  
(인)
To: Chairperson of the Institutional Review Board, Sungkyunkwan 
University