A pragmatic multi-setting lifestyle intervention to improve leisure-time physical activity from adolescence to young adulthood: the vital role of sex and intervention onset time

The long-term effectiveness of healthy lifestyle interventions on improving leisure-time physical activity (LTPA) in adolescents and its factors in low- and middle-income communities is unclear. This study is the first to investigate LTPA trends in a population of Iranian adolescents who underwent a multi-setting lifestyle intervention, considering sex and the time of intervention onset. Participants were 2374 adolescents (57.2% girls), aged 12-18 years, who participated in the Tehran Lipid and Glucose Study (TLGS) during 1999-2001 and followed for a median follow-up of 15.9 over five data points every 3 years. Adolescent participants were assigned to the intervention or control groups based on their residential areas. Boys and girls were categorized into 12-15 or 16-18 years old to minimize participants' bio-psychological differences, facilitate environmental interventions by more compliance with the Iranian educational system and identify the best time to start the intervention. All adolescents in the intervention area received healthy lifestyle interventions via the school-, family-, and community-based programs. LTPA was assessed using the reliable and validated Iranian Modifiable Activity Questionnaire (MAQ) version over the five data points. The Generalized Estimating Equations method was used to evaluate educational intervention's effect on LTPA in adolescents during the follow-up. In boys who experienced the early onset of intervention (12-15 years), the interaction effect of follow-up examinations and the intervention was significant where the impact of the intervention differed over time. In this group, LTPA was higher in the control group than in the intervention group at the first follow-up examination (β = - 1088.54). However, an increasing trend of LTPA was observed in the intervention group until the third follow-up examination (β = 1278.21, p = 0.08, and β = 1962.81, p = 0.02, respectively), with borderline significance levels at the 2nd (P = 0.08) and the 4th (P = 0.08) measurements. The interaction terms and main effects of intervention and follow-up examinations were not significant in boys with late intervention onset. Although older boys in the intervention group had higher LTPA than the control group, there were no significant differences among study groups in all follow-up examinations. Regarding girls, LTPA did not differ significantly between intervention and control groups in all follow-up examinations (P > 0.05). Our results show