The Effect of Vaginal Somatovisceral Pain on Hip Extension Mobility and Strength in Women at Mid-cycle With Dysmenorrhea vs. Controls: A Case-control Study
Phase: NA
Conditions: Dysmenorrhea, Dysmenorrhea Primary, Visceral Pain, Menstrual Pain
Sponsor: Azusa Pacific University

ClinicalTrials.gov Submission Cover Page 
 
Institution / Sponsor Name: ________Azusa Pacific University______________________ 
 
Official Study Title: 
The effect of vaginal somatovisceral pain on hip extension mobility and strength in women 
at mid-cycle with dysmenorrhea vs. controls: A case-control study 
ClinicalTrials.gov Identifier (NCT Number): 
NCTXXXXXXXX (not yet assigned) 
Document Type: 
• Study Protocol with Statistical Analysis Plan 
 
Document Date: 
July 28, 2025 
 
Principal Investigator: 
Megan Steele, PT, DPT, PhD(c) -PI 
Derrick Sueki, PT, PhD, DPT – co-PI, PhD advisor 
 
Azusa Pacific University, Rehabilitation and Movement Science 
 
Sponsor / Collaborators: 
NA 
 
 
 

Methods 
Participants 
Sixty healthy, non-pregnant female participants aged 18–36 will be recruited from Azusa 
Pacific University and Mount Saint Mary’s University, and via a social media account not 
associated with any research team member. All participants will complete a phone screen with the 
primary investigator before the initial visit. The experimental group will consist of at least 30 
subjects with a pain rating during menstruation greater than or equal to 4 on a visual analog scale 
(VAS). The control group will consist of at least 30 age-matched participants with a pain rating 
less than or equal to 3 during menstruation. Inclusion criteria include regular menstrual cycles 
(between 27 and 34 days) and no known medical conditions. All participants will be provided 
written informed consent, and the Azusa Pacific internal review board will approve the study. 
Participants will be provided informed consent prior to participation.  
Exclusion criteria included a history of chronic pain, currently pregnant, having given 
birth within the previous 6 months, currently breastfeeding, or undergoing in-vitro fertilization 
treatments. Those with a history of abdominal or pelvic surgery in the last 3 months will be 
excluded, as well as those with a history of pelvic pathology, including interstitial cystitis, 
endometriosis, pelvic inflammatory disease, and irritable bowel syndrome. Women with a history 
of sexual assault will be excluded, as well as those who are anovulatory without hormonal BC or 
amenorrheic, neurological disorders, significant orthopedic injuries affecting the lower 
extremities, or gastrointestinal conditions that could influence visceral pain perception. 
Participants will also be excluded if they cannot read or comprehend the informed consent 
document in English.  
Examiners 
All assessments will be performed by trained researchers using standardized 
measurement techniques. The same three examiners will participate in each trial.  
Examiner 1 (M.S.) will be responsible for giving informed consent, overseeing the 
experiment, recording any abnormal events in a notebook, and assisting with the setup and 
breakdown of equipment before and after testing. During the screening visit, Examiner 1 will also 
train participants to use the luteinizing hormone (LH) test kits and heart rate variability (HRV) 
test on their phones and instruct them to add the menstrual tracking calendar to their Google 
documents during the initial session. Examiner 1 will also be responsible for passively lowering 
the test leg and holding the dynamometer for strength testing. 
Examiner 2 (J.F.) will be responsible for meeting the participants in the parking lot, 
giving them the parking pass, and escorting them into the research lab. She will also instruct the 
participants where they can go to void their bladder prior to testing. Examiner 2 will also be 
responsible for the insertion of the probe into the subject’s vaginal canal and the inflation of the 

barostat bulb. Examiner 2 will also relay the amount of air in the bulb when the participant 
experiences pain to Examiner 3. 
Examiner 3 (L.D). will be responsible for placing the HRV electrodes on participants and 
mark in the HRV graph during each phase of the study. She will then place a mark on the greater 
trochanter and most posterior portion of the lateral epicondyle with an erasable marker and 
measure the distance between those two points. Once the participant is supine, this examiner will 
mark and record 5 minutes of baseline HRV data. She will then ask the participants to count their 
heartbeats for 3 time periods and their confidence in the count and record the results. Examiner 
Three will also place the biofeedback bladder under the participant’s lumbar spine, monitor the 
dial, and instruct Examiner 1 to stop lowering the participant’s test leg when the dial changes by 
five mmHg. Examiner 3 will then measure and record the distance from the floor to the mark on 
the lateral epicondyle. This examiner will also read and record the number on the dynamometer 
after each manual muscle test of the participant.  
Screening Visit 
At the initial screening visit, participants will be given informed consent and will be asked to 
fill out demographic questionnaires regarding medical, surgical, and gynecological history. Half 
of the 60 anticipated participants will fill out questionnaires regarding pain, interoceptive 
awareness, and quality of life at this visit, and the other half will fill out these questionnaires after 
the second visit to determine of questionnaires contribute to bias. Participants will be taught how 
to download an HRV app (Welltory) and measure their HRV via their phone camera. They will 
be instructed to take a one-minute measure of HRV once daily for 30 days, beginning on the first 
day of their period. Participants will be given an LH test kit and educated on performing LH tests 
daily beginning on day 10 of their menstrual cycle. 
Participants will be asked to inform the research team when they detect a hormone spike via 
the LH kit. They will then be asked to report to the research laboratory in a sports bra without an 
underwire within 10 days of the spike, or during the luteal phase.  
Confirming cycle status 
Because the menstrual cycle phase has been shown to have an effect on pain thresholds, 
the menstrual cycle tracking document and LH test kits will be used to ensure participants are in 
the luteal phase during testing. Participants will be asked to report to the research lab within 10 
days of a positive hormone spike on their LH test kit or days 15-25 of the menstrual cycle per 
CRAMPP studies (Hellman et al., 2020).  
Ensuring Privacy and Safety 
To ensure participant privacy and maintain a controlled testing environment, all 
assessments will be conducted in a private examination room with closed doors and covered 
windows to prevent external visibility. A sign will be placed outside the door to indicate that 

testing is in progress, minimizing the risk of unintended entry. In the event that someone 
inadvertently enters, a privacy screen will be positioned between the participant and the door to 
prevent visual exposure and auditory privacy will be maintained by limiting conversations to 
necessary instructions in a low-volume, professional manner.  
To safeguard the health of both examiners and participants, examiners will wear gloves 
and any necessary protective equipment during physical assessments of the visceral system. Some 
equipment, including chucks, ECG electrodes, and measuring devices, will be new and sterile for 
each participant. Equipment shared between participants, including gowns, linens, markers, 
dynamometers, and biofeedback bladder, will be sterilized between sessions to reduce the risk of 
cross-contamination. Hand hygiene protocols will be strictly followed, with examiners washing 
or sanitizing their hands before and after each session. 
Experimental Protocol 
The study will assess the impact of a visceral, painful stimulus on the autonomic nervous 
system, hip flexor mobility and dorsiflexor strength using a standardized protocol involving a 
barostat probe. Testing will be conducted in a temperature-controlled laboratory setting separated 
from the rest of the lab area by a tent with opaque walls to ensure privacy. 
Preparation and Baseline Measurements 
1. Participants will be met outside the building and given a parking pass to place on their 
dashboard. They will then be led into the testing room by the same researcher. 
2. They will be instructed to void their bladder before entering the testing room. 
3. Upon entry, participants will be instructed to change into a hospital gown and disposable 
underwear in the privacy of the testing tent. 
4. Anatomical landmarks will be identified, and small circular marks will be placed on 
the greater trochanter and the most posterior portion of the lateral femoral epicondyle of 
the tested limb. 
5. The distance between these markers will be measured as a calculation reference, and the 
distance between the marks and the floor will be used to measure hip flexor mobility. 
Heart Rate Variability Assessments 
6. HRV data will be recorded throughout the experiment to determine autonomic nervous 
system responses with Biopac MP36, three electrode system. 
7. Participants will be positioned supine on an examination table, and heart rate variability 
(HRV) electrodes will be applied following standardized lead placement. 
8. Within 15 minutes of electrode placement, a five-minute baseline HRV recording will be 
conducted under resting conditions per task force guidelines (Malik et al., 1996). 
Interoceptive Assessments 
9. Interoceptive accuracy will be assessed using a heartbeat-tracking task, with eyes open, 
participants will be asked to count their heartbeats for 25, 35, and 45-second intervals to 
quantify interoception. 

10. Interoceptive confidence will be recorded using a 10 mm visual analog scale (VAS). 
Participants will be asked to mark the scale according to how confident they felt about 
their heart rate in the accuracy assessment.  
Baseline Musculoskeletal Assessments 
10. Hip flexor mobility will be analyzed via changes in marker distance from the floor, while 
dorsiflexor strength will be quantified in Newtons using the handheld dynamometer. 
11. During the hip flexor measurements, a small inflatable bladder will be inflated to 40 mm 
Hg (Azevedo et al., 2013) and placed under the participant’s lumbar spine to decrease 
movement from the pelvis and lumbar spine. 
12. The untested leg will be positioned at 70 degrees of hip flexion to limit compensatory 
movement and standardize the position. The test leg will rest on a stool below the test 
table. 
13. Hip flexor mobility will be assessed through two repeated trials using passive hip 
extension range-of-motion measurements. The test leg will be placed on the stool to rest 
between trials. Examiner 1 will passively lower the leg while Examiner 3 observes the 
dial on the biofeedback bladder. When the number on the biofeedback dial moves 5mm 
of Hg, examiner 1 will stop moving the participant’s leg, and a measurement will be 
taken using a stadiometer (model 213, Seca, Birmingham, UK) by examiner 3. 
Calculations will be completed using the trigonometric technique as described by 
Wakefield et al. (2015) due to the improved reliability over goniometric measurements. 
An average of the two measurements will be taken.  
14. Dorsiflexion strength will be measured via a handheld dynamometer (Hoggan Scientific 
Microfet 2). Dorsiflexor strength will be measured using a ‘make it’ technique (Spink et 
al., 2010) with a handheld dynamometer. In this technique, the examiner will hold the 
dynamometer stationary while the participant pushes against it with maximal force. 
Verbal encouragement will be given by examiners 1 and 3. After each trial, Examiner 1 
will hold the dynamometer, allowing Examiner 3 to read and record the value. Two 
maximal voluntary contractions will be recorded and averaged, each separated by a one-
minute rest period to mitigate fatigue. 
Visceral Pain Stimulation 
15. Participants will be asked to avoid taking long or short-acting over-the-counter analgesics 
for at least 6 hours before the assessment visit.  
16. Participants will be given standardized information about the barostat probe by Examiner 
2, who is credentialed by the APTA to complete internal pelvic exams. 
17. To ease entry, the barostat probe will be lubricated with a water-based lubricant (Slippery 
Stuff, Wallace-O’Farrell, Inc., Puyallup, WA).  
18. The probe will be inserted 2 inches into the vaginal canal with the participant in a supine 
position with lower extremities externally rotated to allow for probe insertion. 
19. Following insertion, participants will resume the supine position with the test leg resting 
on a stool and the non-test leg at 70 deg flexion in the sagittal plane. Next, post-insertion 
musculoskeletal assessments will be conducted as described above: 
1. Hip flexor mobility test (two trials) 
2. Dorsiflexor strength test (two trials) 
Visceral Pain Stimulation and Reassessment 

20. The barostat probe will be inflated twice to allow the participant to experience the 
sensation.  
21. Next, the barostat will be inflated to induce a visceral, painful stimulus at a pressure level 
individualized to the participant’s tolerance. Participants will be asked to state verbally 
when they perceive the sensation as painful.   
22. The amount of air in the probe will be noted by Examiner 2 and relayed to Examiner 3, 
and the bulb will be deflated. 
23. Immediately following deflation, hip flexor mobility, and dorsiflexor strength will be 
reassessed as described above: 
1. Hip flexor mobility test (two trials) 
2. Dorsiflexor strength test (two trials) 
Post-testing Instruction and Procedures 
Finally, Examiner 2 will remove the probe and allow the participant to sit up on the edge 
of the plinth. Examiners 2 and 3 will leave the testing area, and Examiner 1 will confirm that the 
participant feels safe enough to stand, and she will be given a wipe to clean herself and privacy to 
change back into her clothes. Once fully clothed, the participant will be informed that some 
spotting and soreness may be present for the next two days. The participant will be reminded of 
the on-site healthcare options and instructed to notify her medical team if she experiences any 
adverse effects, as detailed in the informed consent. Any further questions from the participant 
will be answered by the primary investigator at this time. The participant will be thanked and 
escorted out of the lab.  
 
Data analysis plan 
Version 27 of IBM SPSS statistics will be used to analyze the recorded data. To 
determine homogeneity between groups, the baseline characteristics of the 2 groups will be 
analyzed using the t-test or nonparametric equivalent for continuous variables and chi-squared 
test for categorical variables. If participants are not able to complete all conditions, their scores 
will be removed via listwise deletion. Prior to data analysis, assumptions will be assessed. 
The correlational analysis will be completed to determine the relationship between the 
variables of interest. 
Regression analysis will be performed to determine the potential for variables of interest 
to predict outcomes in the dependent variable.  
A repeated measures ANOVA (RM-ANOVA) will be used for comparing the 
means of the same subjects across multiple conditions (baseline, probe insertion, 
and probe inflation). This method can determine whether there are statistically 
significant changes in hip flexor mobility, dorsiflexor strength, or HRV measures 
over time. Assumptions include sphericity, which can be tested and corrected (e.g., 
using the Greenhouse–Geisser correction) if violated. 

The independent variables include pain with menstruation, pain stimulus, and HRV. The 
dependent variables are the change in hip mobility and dorsiflexor strength following a painful 
stimulus.