Severity of slouched posture during smartphone use is associated with the musculoskeletal discomfort, daily usage, and school year among adolescents.

Real-time measurement of the craniovertebral, thoracic kyphosis, and lumbar lordosis angles during natural and smartphone usage postures in sitting were analysed in a cohort of 560 adolescents using independent t -tests and Spearman's correlations between their reported musculoskeletal symptoms, daily device use and school year. Students with musculoskeletal symptoms (mean difference: 4.1-9.4°, p  < .001) and in secondary schools (mean difference: 13.6-29.4°, p  < .001) had a greater forward-head posture quantified by craniovertebral angle in both postures. Loss of lumbar lordosis was found in students spending ≥2 h/day on electronic devices (mean difference: 3.2°, p  = .029) and those with musculoskeletal symptoms (mean difference: 5.4°, p  = .001). Secondary school students exhibited a greater thoracic kyphosis when using smartphones (mean difference: 3.3°, p  = .003). Findings suggest the urgent need for early and proactive intervention targeted to minimise the risk of developing musculoskeletal disorders related to intense device use for young adolescents. Practitioner Summary: Adolescents: (1) in higher school year had increased forward-head posture (FHP) and thoracic kyphosis; (2) with musculoskeletal symptoms had increased FHP and loss of lumbar lordosis, and; (3) with extended device use had a loss of lumbar lordosis. Early intervention targeting young adolescents promoting optimal posture and habit of device use is warranted.