Dose-dependent Association between Smartphone Usage and Upper Body Postural Alterations in Young Adults: A Cross-sectional Study

Background: Prolonged smartphone use is increasingly associated with cervicothoracic postural dysfunction. Quantitative data correlating specific usage patterns with objective postural parameters remain limited in South Asian populations. Objective: The objective of this study was to evaluate upper body postural changes in young adults using digital photogrammetry and determine dose-dependent correlations between daily smartphone usage and postural deviations. Materials and Methods: A cross-sectional study recruited 131 participants (68 males, 63 females; aged 18–25 years) stratified into three groups: Group I (<2 h/day, n = 45), Group II (2–5 h/day, n = 43), and Group III (>5 h/day, n = 43). Postural parameters – craniovertebral angle (CVA), scapular index (SI), and thoracic kyphosis index – were measured using standardized digital photogrammetry. One-way analysis of variance, Tukey’s honestly significant difference post hoc tests, and Pearson correlation analyses were performed. Results: CVA declined significantly across groups (Group I: 48.7° ± 3.1°; Group II: 45.9° ± 3.8°; Group III: 42.6° ± 3.4°; P < 0.001). SI increased progressively (Group I: 68.2 ± 4.7; Group III: 73.8 ± 5.6; P < 0.001). Moderate-to-severe thoracic kyphosis was found in 74.4% of Group III participants. Strong correlations were confirmed between daily usage and CVA ( r = −0.758, P < 0.001) and SI ( r = 0.742, P < 0.001). Conclusion: Smartphone use demonstrates a dose-dependent association with forward head posture, scapular protraction, and thoracic kyphosis in young adults. Early ergonomic intervention and postural reeducation are recommended.