The effect of screen viewing distance restriction on self-correction exercise in smartphone users

INTERVENTION: Behavioral : Both groups performed McKenzie cervical exercise three times per week for four weeks. The programme comprised seated neck retraction, extension, lateral flexion, rotation, and flexion, plus supine chin tuck and neck extension; each movement was performed as 15 repetitions of a 7‐second contraction followed by a 7‐second hold. The first session was conducted in person with a guided instructional video under supervision; subsequent sessions were performed independently at home and logged in a shared online spreadsheet. The control group (CG) performed McKenzie exercise only. The experimental group (EG) additionally kept the iPhone Screen Distance feature switched on throughout the four weeks; when the device was held closer than 30 cm for a prolonged period, a full‐screen alert appeared and use could resume only after the device was moved more than 30 cm away. The only difference between groups was the use of the Screen Distance feature. CONDITION: Diseases of the musculoskeletal system and connective tissue PRIMARY OUTCOME: Craniovertebral angle (CVA) — the angle between the horizontal line through C7 and the line from C7 to the tragus of the ear, measured from a photograph (taken at 60 cm) using ImageJ SECONDARY OUTCOME: Neck Disability Inde X(NDI) — neck‐related disability assessed across 10 items, each scored 0 to 5 Numeric Rating Scale (NRS) — self‐reported headache and neck pain intensity rated from 0 to 10 Smartphone viewing distance — distance (cm) between the eyes and the smartphone screen, recorded during photographic assessment INCLUSION CRITERIA: 1) Adults aged 19–29 years 2) Ownership of an iPhone running iOS 17 or later (required for the Screen Distance feature) 3) Presence of forward head posture, defined as a craniovertebral angle (CVA) below 53 degrees on baseline photographic assessment