Longitudinal associations between physical activity-sedentary time balance and internalizing/externalizing problems in children

Background: Quantifying the dynamic interplay of waking movement behaviors, particularly physical activity (PA) and sedentary behavior (SB), through specific metrics such as the Physical Activity-Sedentary Time Balance index (PASTBI), has recently received increasing research attention in adults. However, there is a paucity of longitudinal studies applying this metric to elucidate potential associations with mental health in children. Thus, applying this approach offers a promising potential to improve our understanding of the long-term implications of movement behaviour balance on children's mental health trajectories, with important implications for intervention design. Methods: PA and SB of 5123 children were measured at age 7 using accelerometers, while mental health problems at age 11 were assessed using the Strengths and Difficulties Questionnaire. Specifically, PASTBI, defined as daily PA minutes divided by daily SB minutes, was categorized into 4 sex-based quartiles (Q1-Q4). Linear regression models were used to examine sex-stratified associations of PASTBI-related quartiles at age 7 years with internalizing and externalizing problems at 11 years. Results: Among boys, those in quartiles 3 and 4 of PASTBI at age 7-reflecting higher PA and lower SB-showed significantly lower internalizing scores at age 11 compared with boys in quartile 1 (eg., Q4: B = −0.841, 95% CI: −1.154 to −0.528). A higher PASTBI (Q4 versus Q1) was associated with higher externalizing problem scores at age 11 in both boys (B = 0.705, 95% CI: 0.409 to 1.002) and girls (B = 0.702, 95% CI: 0.421 to 0.983). Conclusion: Higher PA and lower SB levels are associated with fewer internalizing problems in boys, but with more externalizing problems across both boys and girls, suggesting a complex association between the balance of SB and PA with mental health in children. Future research, which investigates the role of developmental and contextual moderators, is required before more solid conclusions on the optimal balance of waking movement behaviors for mental health can be drawn.