Improper sitting posture mediates the association between single-shoulder backpack carrying and back pain in adolescents: a cross-sectional and longitudinal analysis.

BACKGROUND

The association between single-shoulder backpack carrying and back pain in adolescents remains unclear. This study investigated whether the degree of improper sitting posture mediates the relationship between single-shoulder backpack carrying and back pain in both cross-sectional and longitudinal analyses.

METHODS

This study collected data from a school-based sample covering nine provinces in China from 2021 to 2025. Back pain and backpack carrying mode were assessed through self-reporting. Improper sitting posture was scored using a three-item scale endorsed by the Chinese Ministry of Education. A cross-sectional analysis was conducted on 3,420 participants, and a longitudinal analysis was conducted on 2,423 participants. Multivariate logistic regression and Cox proportional hazards models were used to evaluate the associations between single-shoulder backpack carrying, improper sitting posture, and back pain. Mediation analysis was used to assess the mediating role of improper sitting posture in the association between single-shoulder backpack carriage and back pain. Subgroup analyses were conducted to evaluate effect modification across prespecified subgroups. Statistical significance was set at p < 0.05 (two-sided).

RESULTS

In the cross-sectional analysis, single-shoulder backpack carrying (OR = 1.402, 95%CI: 1.128-1.742, p = 0.002) and improper sitting posture (OR = 2.029, 95%CI: 1.695-2.430, p < 0.001) were both positively associated with back pain. Improper sitting posture accounted for 37.42% of the association between the single-shoulder backpack carrying and back pain. In the longitudinal analysis, single-shoulder backpack carrying (HR = 2.147, 95% CI: 1.565-2.945, p < 0.001) and improper sitting posture (HR = 1.885, 95% CI: 1.473-2.412, p < 0.001) were both positively associated with back pain. Improper sitting posture accounted for 11.45% of the association of single-shoulder backpack carrying with back pain.

CONCLUSION

Single-shoulder backpack and improper sitting posture were significantly and positively associated with back pain, and improper sitting posture partially mediated the association between single-shoulder backpack carrying and back pain. These results suggest that modifying backpack carrying mode and improving improper sitting posture may be associated with a lower likelihood of back pain in adolescents.