Social networks, social isolation and leisure-time physical activity in Brazilian adolescent students.

The objective of this article is to investigate the association between social networks, social isolation, and leisure-time physical activity among Brazilian schoolchildren. This national cross-sectional study included 101,927 9th-grade students (aged 13-15) from 3,040 schools. Leisure-time physical activity was assessed based on frequency and duration over the previous seven days and categorized into four levels: ≥300, 150-299, 1-149, and 0 minutes per week. Social isolation and social networks were measured by the frequency of feeling lonely and the number of close friends. Multinomial logistic regression estimated unadjusted and adjusted odds ratios. After adjusting for sociodemographic and behavioral factors, students who always felt isolated had 26% higher odds of being completely inactive compared to those who never felt isolated. Those with no close friends had 69% higher odds of complete inactivity versus those with three or more friends. Health promotion initiatives should address the role of peer relationships and social connectedness in shaping adolescents' physical activity patterns.