An interventional study of Preferred/High-Interest Smartphone Video Viewing and Neutral/Lower-Interest Smartphone Video Viewing in Neck Discomfort During Smartphone Use, sponsored by Karabuk University. Not yet recruiting at 1 site in Turkey (Türkiye). Open to participants aged 18 Years to 30 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-10-30.
Sponsored by Karabuk University · Not applicable, Interventional, and Basic science
This study will examine whether personal interest in smartphone video content changes neck discomfort, posture, and pressure pain sensitivity in young adults. One hundred regular smartphone users aged 18 to 30 years will complete two 30-minute video-viewing sessions, separated by 48 to 72 hours. One session will use personally preferred, high-interest content and the other neutral, lower-interest content. The order will be randomly assigned. The same study phone, stand, seating, and viewing setup will be used in both sessions. Neck and shoulder discomfort will be recorded during viewing, neck and trunk posture will be measured from video, and pressure pain threshold will be assessed before and after viewing. Engagement, enjoyment, and emotional responses will also be measured. The main comparison is neck discomfort at minute 30 between the two content conditions.
This is a single-center, two-condition, two-period randomized crossover experiment at Karabuk University, Faculty of Health Sciences, Department of Physiotherapy and Rehabilitation. One hundred participants will be allocated 1:1 to sequence AB or BA. A is preferred/high-interest video content; B is neutral/lower-interest content. Sequence allocation will be computer-generated by a researcher not involved in measurement and concealed in numbered sealed envelopes. Sessions will be separated by 48-72 hours and scheduled at similar times of day where possible.
A separate preparatory pilot involving up to 12 volunteers will test workflow and technical procedures. Pilot observations will not enter the main hypothesis analyses or the main enrollment target of 100. Substantial protocol changes after the pilot will require an ethics amendment before the main study.
Videos will be selected from a standardized pool matched as closely as possible for duration, resolution, volume, subtitles, and presentation. After short previews, interest/enjoyment ratings will identify preferred/high-interest and lower-interest content that does not evoke negative emotion. Violent, frightening, sexual, or strongly negative material will not be used. Both conditions involve video viewing only.
Participants will sit comfortably in an adjustable chair with back support and use the same study smartphone and adjustable stand. Screen position, distance, brightness, sound, room lighting, seating, and camera setup will be reproduced across sessions. Natural head and trunk movements will be allowed during each 30-minute session.
Neck and bilateral shoulder discomfort will be recorded at baseline and minutes 10, 20, and 30 using the 0-10 Borg CR-10 discomfort scale. The primary endpoint is neck discomfort at minute 30. Sagittal video-photogrammetry will assess neck and trunk angles at minutes 0, 5, 10, 15, 20, 25, and 30. Markers will be placed at the tragus, C7, T12, and greater trochanter. Neck flexion is defined by the tragus-C7 line relative to vertical; trunk angle is formed by the C7-T12 and T12-greater trochanter lines. Kinovea will be used for coded-image analysis by a trained assessor who will be unaware of the content condition where possible. Participants cannot be blinded to their own preferences.
Digital algometry will measure pressure pain threshold bilaterally at the upper trapezius and at the dominant tibialis anterior before and immediately after viewing. A 1 cm2 probe will apply pressure at approximately 30 kPa/s, stopping at first pain. Three measurements per site will be averaged, with 30-60 seconds between measurements. Measurement order will be maintained across sessions.
The Turkish Extended Nordic Musculoskeletal Questionnaire will describe baseline symptoms. End-of-session assessments will include the Turkish Flow Short Scale, interest/enjoyment subscale of the Turkish Intrinsic Motivation Inventory, and Self-Assessment Manikin valence and arousal ratings. Baseline sleep, recent intense physical activity, caffeine, analgesic use, and discomfort will be recorded to assess session comparability and deviations.
Mixed-effects models will include condition, time, condition-by-time, period, and sequence, with participant as a random effect. The primary analysis compares minute-30 neck discomfort within participants. Additional models will include neck and trunk angles to explore the relationship independent of measured postural exposure. Pressure pain threshold will be examined with condition-by-time (pre/post) interaction. Effect sizes and 95% confidence intervals will be reported with two-sided alpha 0.05.
Participants may stop at any time. Marked pain, dizziness, numbness/tingling, visual discomfort, or unwillingness to continue will end the task immediately. All data and images will be coded. Identifiable images will not be published or presented without separate explicit written permission.
Karabuk University is the lead sponsor of 142 studies on the registry; 39 are open to participants now.
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Participants first view preferred/high-interest video content for 30 minutes, then neutral/lower-interest content for 30 minutes in the second session after a 48-72-hour interval. Both sessions use the same study smartphone, stand, chair, and viewing setup.
Behavioral: Preferred/High-Interest Smartphone Video Viewing · Behavioral: Neutral/Lower-Interest Smartphone Video Viewing
Participants first view neutral/lower-interest video content for 30 minutes, then preferred/high-interest content for 30 minutes in the second session after a 48-72-hour interval. Both sessions use the same study smartphone, stand, chair, and viewing setup.
Behavioral: Preferred/High-Interest Smartphone Video Viewing · Behavioral: Neutral/Lower-Interest Smartphone Video Viewing
Thirty minutes of seated viewing on a standardized study smartphone and adjustable stand. Content is selected from a standardized pool after preview-based interest/enjoyment ratings, choosing personally preferred/high-interest material without strongly negative emotional content. Device, sound, screen brightness, seating, viewing position, and environment are matched to the neutral condition.
Thirty minutes of seated video viewing using lower-interest content from the same standardized pool, selected to avoid negative emotion. Duration, resolution, volume, subtitles, presentation, smartphone, stand, seating, viewing position, brightness, and room setup are matched as closely as possible to the preferred/high-interest condition.
Neck Discomfort at Minute 30
Perceived neck discomfort measured with the 0-10 Borg CR-10 discomfort scale, where 0 indicates no discomfort and higher scores indicate greater discomfort. The primary endpoint is the within-participant difference between preferred/high-interest and neutral/lower-interest content conditions at minute 30.
Time frame: At minute 30 of each of two sessions, separated by 48-72 hours
Neck Discomfort Over Time
Repeated perceived neck discomfort on the 0-10 Borg CR-10 scale. Higher values indicate greater discomfort.
Time frame: Baseline and minutes 10, 20, and 30 in each session; sessions 48-72 hours apart
Right and Left Shoulder Discomfort
Right and left shoulder discomfort measured separately using the 0-10 Borg CR-10 scale. Higher values indicate greater discomfort; sides are analyzed separately.
Time frame: Baseline and minutes 10, 20, and 30 in each session; sessions 48-72 hours apart
Neck Flexion Angle
Sagittal neck flexion angle in degrees between the tragus-C7 line and vertical, measured from standardized video frames using Kinovea.
Time frame: Minutes 0, 5, 10, 15, 20, 25, and 30 of each session; sessions 48-72 hours apart
Trunk Angle
Sagittal trunk angle in degrees formed by the C7-T12 and T12-greater trochanter lines, measured using Kinovea from standardized video frames.
Time frame: Minutes 0, 5, 10, 15, 20, 25, and 30 of each session; sessions 48-72 hours apart
Task Engagement and Flow
Task engagement and flow assessed with the Turkish Flow Short Scale. The flow score reflects absorption and fluency during the video-viewing task; higher flow scores indicate greater flow experience.
Time frame: Immediately after each 30-minute session; sessions 48-72 hours apart
Interest and Enjoyment
Interest/enjoyment assessed with the interest/enjoyment subscale of the Turkish Intrinsic Motivation Inventory. Higher scores indicate greater intrinsic interest and enjoyment; used as a manipulation check.
Time frame: Immediately after each 30-minute session; sessions 48-72 hours apart
Emotional Valence and Arousal
Self-Assessment Manikin pictorial ratings of emotional valence and arousal, reported separately. Valence reflects unpleasant-to-pleasant affect; arousal reflects calm-to-excited activation. Used to characterize the emotional response to content.
Time frame: Immediately after each 30-minute session; sessions 48-72 hours apart
Pressure Pain Threshold
Exploratory mechanistic outcome measured in kPa with calibrated digital algometry at the right and left upper trapezius and dominant tibialis anterior. A 1 cm2 probe is applied perpendicular to the skin at approximately 30 kPa/s until first pain. Three readings per site are averaged, with 30-60 seconds between readings. Higher values indicate lower pressure pain sensitivity. Sites are analyzed separately.
Time frame: Before and immediately after each 30-minute session; sessions separated by 48-72 hours
Plan to share: Undecided
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