Predictors of Pressure Pain Thresholds

Study Protocol Study Design This is a cross-sectional, observational study conducted at Dokuz Eylul University between October 2023 and August 2024. All procedures comply with the Declaration of Helsinki. Ethical approval was obtained from the Institutional Noninvasive Research Ethics Board (Approval number: 2023/31-23, Date: 4 October 2023). Written informed consent was obtained from all participants before data collection.

Participant Recruitment and Screening

Office workers at Dokuz Eylul University are recruited through workplace announcements. A two-stage screening process determines eligibility:

Inclusion Criteria:

Office workers aged 25-44 years

Body mass index (BMI) between 18.5 and 29.9 kg/m²

Presence of at least one latent trigger point (LTrP) in the upper trapezius muscle

Voluntary written informed consent

Exclusion Criteria:

History of head, neck, or shoulder surgery

Any condition that may be confused with myofascial pain (e.g., fibromyalgia, cervical radiculopathy)

Any condition altering pain sensation or tissue characteristics (e.g., neuropathy, diabetes)

Presence of an active trigger point (spontaneous pain) in the upper trapezius

Use of painkillers or anti-inflammatory drugs within 24 hours

Myofascial pain treatment within the last 3 months

BMI \< 18.5 or > 29.9 kg/m²

Pregnancy

Study Procedures All assessments are conducted one hour after participants begin their workday to allow for postural adaptation to their workspace. Each assessment session lasts approximately 40 minutes.

1. Demographic and Time-Use Data Collection

   Age, sex, weight, height, and BMI are recorded

   Years of employment in office-based work are documented

   Weekly phone screen time is obtained from mobile device digital wellbeing trackers (Screen Time for iOS or Digital Wellbeing for Android)

   Weekly computer use time and daily sitting time are self-reported

   Total weekly screen time is calculated by combining phone and computer hours

2. Latent Trigger Point Identification Participants receive brief education on differentiating active from latent trigger points. Those reporting spontaneous pain are excluded.

   Manual pincer palpation is performed bilaterally on the upper trapezius muscles by an experienced physiotherapist (12 years clinical experience, 5 years specializing in myofascial pain). Palpation follows the muscle from the nuchal line origin to the acromion insertion. An LTrP is confirmed by:

   Localized tenderness

   A palpable taut band

   A hypersensitive spot eliciting referred pain upon compression (without spontaneous symptoms)

   The most painful LTrP is marked with a permanent marker. A second palpation one minute later verifies the LTrP count; a third palpation is performed if discrepancies exist.

3. Pressure Pain Threshold Assessment PPT is measured using a calibrated Baseline Algometer (10 kg/22 lbs., Fabrication Enterprises, USA). The probe is applied perpendicularly to the skin over the marked trigger point, with pressure increasing at approximately 1 kg/cm² per second. Participants verbally indicate pain onset; the reading is recorded in pounds. The algometer display is concealed from the examiner to prevent bias. The procedure is repeated three times at 30-second intervals, and the mean value is calculated. PPT is also assessed at a standardized non-trigger point area (no tenderness or taut bands) for comparison.

4. Ergonomic Risk Assessment

   The Rapid Office Strain Assessment (ROSA) tool evaluates ergonomic risk factors including:

   Chair components (seat height, depth, armrests, back support)

   Monitor position (height, distance, angle)

   Telephone placement

   Keyboard and mouse positioning

   A cumulative score is generated; higher scores indicate greater ergonomic risk.

5. Postural Assessment via Photogrammetry

Head and neck working posture is evaluated using photogrammetric measurement of:

Craniocervical Angle (CCA): Angle between the line connecting the lateral canthus to the tragus, and the line connecting the tragus to C7. Lower CCA indicates more pronounced forward head posture.

Cervicothoracic Angle (CTA): Angle between the line connecting the tragus to C7, and the line connecting C7 to the greater trochanter. Decreased CTA indicates increased thoracic kyphosis or combined forward head and rounded shoulder posture.

Procedure:

Participants wear open-necked clothing; hair is secured away from the face

Adhesive markers are placed on anatomical landmarks (right side preferred): lateral canthus, tragus, C7 spinous process, and greater trochanter

C7 is palpated following established protocols; the greater trochanter is palpated and marked

Participants resume their usual work tasks and undergo a 5-minute adjustment period to minimize the Hawthorne effect

Lateral photographs are captured three times at one-minute intervals from approximately 150 cm distance at acromion height using a tripod-mounted smartphone

Angle measurements are performed digitally using Adobe Acrobat DC; the mean of three measurements is used for analysis

The evaluator performing photographic measurements is blinded to all other participant data

Outcome Measures

Primary Outcome:

Mean Pressure Pain Threshold (PPT) at the most painful latent trigger point in the upper trapezius (measured in lbs/cm²)

Secondary Outcomes:

Number of LTrPs in the bilateral upper trapezius muscles

Mean PPT at non-trigger point site in the upper trapezius

Rapid Office Strain Assessment (ROSA) total score

Craniocervical Angle (CCA) in degrees

Cervicothoracic Angle (CTA) in degrees

Total weekly screen time (hours)

Daily sitting time (hours)

Years of employment in office-based work

Statistical Analysis Plan Sample Size: 67 participants who met all eligibility criteria.

Statistical Software: SPSS Statistics 26.0.

Data Distribution: Normality is assessed using the Kolmogorov-Smirnov test and descriptive statistics. All continuous variables are expected to follow normal distribution.

Primary Analysis:

Hierarchical multiple regression is performed to determine whether ROSA score and CTA predict mean PPT at LTrPs after controlling for demographic variables:

Step 1: Demographic variables (age, gender, BMI, years of employment)

Step 2: ROSA score and CTA added to the model

Significance level: p \< 0.05

Secondary Analyses:

Pearson correlation coefficients are calculated for relationships among PPTs, ROSA score, CCA, CTA, weekly screen time, daily sitting time, years of employment, and demographic variables

Spearman correlation coefficients are used for relationships involving the number of LTrPs

Correlation interpretation:

\<0.10: Negligible

0.10-0.39: Weak

0.40-0.69: Moderate

0.70-0.89: Strong

0.90-1.00: Very strong

Assumption Checking:

Multicollinearity is assessed using Variance Inflation Factor (VIF) and tolerance values. VIF \< 10 and tolerance > 0.2 indicate absence of multicollinearity.