Immediate effects of sitting position on cervical and trunk posture, perceived discomfort, and RULA-based ergonomic risk during smartphone gaming: A randomized within-subject study

Abstract

Objective This study investigated the immediate effects of three sitting positions, including chair sitting with and without a backrest and cross-legged sitting on the floor, on cervical and trunk postures, musculoskeletal discomfort, and ergonomic risk during smartphone gaming among young adults. Methods A randomized within-subject study was conducted in 41 healthy participants (mean age 20.4 ± 1.1 years). Each participant played Realm of Valor (ROV) on their personal smartphone for 20 minutes in three randomly assigned sitting positions. Cervical and trunk angles were measured using two-dimensional photogrammetry at baseline and at 5, 10, 15, and 20 minutes. Ergonomic risk was assessed using the Rapid Upper Limb Assessment (RULA), with the maximum score used for analysis. After each session, participants reported perceived musculoskeletal discomfort using a visual analog scale. Results A significant interaction between time and sitting position was found for both neck flexion (F(3.87, 232.27) = 5.31, p < 0.001, partial η² = 0.081) and trunk angles (F(8,480) = 2.73, p = 0.006, partial η² = 0.044). Perceived neck discomfort was the most common symptom, with the cross-legged position showing the highest prevalence (51.2%, Cochran’s Q = 8.67, p = 0.013, Kendall’s W = 0.106). However, symptom intensity did not differ significantly among positions. RULA scores also differed across sitting positions (χ²(2) = 27.0, p < 0.001, Kendall’s W = 0.329), with the cross-legged position showing the highest score. Conclusion Sitting posture significantly affected cervical and trunk alignment, perceived discomfort, and ergonomic risk during smartphone gaming. Cross-legged sitting induced the greatest neck and trunk flexion, which may contribute to increased musculoskeletal strain over time. These findings emphasize the importance of promoting ergonomic awareness and healthy digital habits to maintain spinal alignment and reduce posture-related musculoskeletal strain; however, longitudinal studies are needed to confirm long-term effects.