Smartphone Screen Time, Standing Postural Alignment, and Pulmonary Function in Healthy Young Adults: An Exploratory Cross-Sectional Study

Background: Prolonged smartphone use has been proposed to influence postural alignment and pulmonary function; however, continuous relationships among these variables remain uncertain in young adults. Methods: Thirty healthy university students completed assessments of device-recorded average daily smartphone screen time over the preceding seven days, craniovertebral and shoulder-C7 angles during natural standing, forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and positive and negative affect. Eight Spearman correlations were evaluated using 5000-resample bootstrap confidence intervals and Holm adjustment for multiple comparisons. Separate linear regression models examined smartphone screen time as a predictor of FVC and FEV1 after adjustment for biological sex and height. Results: None of the primary correlations was statistically significant after Holm adjustment. The largest estimate was observed between smartphone screen time and FVC (ρ = −0.242, 95% CI −0.540 to 0.101; Holm-adjusted p = 1.000). In adjusted models, smartphone screen time was not significantly associated with FVC (B = −0.054 L per additional hour/day, 95% CI −0.127 to 0.019; Holm-adjusted p = 0.280) or FEV1 (B = −0.027 L per additional hour/day, 95% CI −0.123 to 0.068; Holm-adjusted p = 0.561). Secondary exploratory analyses identified an inverse correlation between shoulder-C7 angle and negative affect and positive correlations between FVC and height and body weight. Conclusions: Statistically significant primary associations among seven-day smartphone screen time, standing postural alignment, and pulmonary function were not detected. These findings do not establish that the variables are independent and should be interpreted cautiously given the small sample and wide confidence intervals.