BackgroundPhysical activity is thought to play a role in spinal pain (neck pain, mid back pain, low back pain) in children and adolescents, either as a risk or protective factor, but current evidence is conflicting. The overall aim of this study was to determine the cross-sectional and longitudinal associations between different levels of objectively measured physical activity, i.e. sedentary; moderate and vigorous; vigorous physical activity, and spinal pain in 11-15-year-old Danes. MethodsData were collected at baseline (2010) (n=906) and at follow-up 2years later (n=625) in a school-based prospective cohort study. Physical activity was measured using the Actigraph GT3X TriaxialActivity Monitor, which measures the intensity of physical activity overtime. This was worn for 1week and spinal pain was assessed via e-survey that participants completed during school time. Potential confounders included in the multivariable analyses were sex, anthropometry, physical fitness, social status and psychosocial factors. In the longitudinal study, analyses stratified by baseline pain status were performed. ResultsThere were neither cross-sectional nor longitudinal associations between different levels of objectively measured physical activity and spinal pain over the 2-year period. ConclusionObjectively measured physical activity was not associated with spinal pain. However, it remains to be seen whether there is an association over a longer follow-up period. Future research should focus on the more qualitative aspects of physical activity, such as different sports activities.