Students who always felt isolated had 26% higher odds of being completely inactive, and those with no close friends had 69% higher odds of complete inactivity, suggesting that peer relationships and social connectedness shape adolescents' physical activity patterns.
Key Findings
Results
Students who always felt socially isolated had significantly higher odds of being completely physically inactive during leisure time.
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.
Social isolation was measured by the frequency of feeling lonely.
Leisure-time physical activity of 0 minutes per week was the reference category for complete inactivity.
The study used multinomial logistic regression to estimate unadjusted and adjusted odds ratios.
Results
Having no close friends was associated with substantially higher odds of complete physical inactivity during leisure time.
Students with no close friends had 69% higher odds of complete inactivity versus those with three or more friends.
Social networks were measured by the number of close friends.
This association was observed after adjusting for sociodemographic and behavioral factors.
The comparison group was students with three or more close friends.
Methods
This was a large national cross-sectional study of Brazilian 9th-grade students examining social factors and physical activity.
The study included 101,927 9th-grade students aged 13-15 years.
Students were drawn from 3,040 schools across Brazil.
Leisure-time physical activity was assessed based on frequency and duration over the previous seven days.
Physical activity was categorized into four levels: ≥300, 150-299, 1-149, and 0 minutes per week.
Results
Both social isolation and limited social networks were independently associated with lower levels of leisure-time physical activity in adolescents.
Two distinct social dimensions were examined: feeling lonely (social isolation) and number of close friends (social networks).
Both measures showed associations with complete physical inactivity after adjustment for confounders.
Sociodemographic and behavioral factors were included as covariates in the adjusted models.
The findings suggest peer relationships and social connectedness shape adolescents' physical activity patterns.
Conclusions
The authors concluded that health promotion initiatives should address peer relationships and social connectedness as factors influencing adolescent physical activity.
The study identifies social isolation and limited social networks as risk factors for physical inactivity in adolescents.
The authors recommend that health promotion initiatives target the role of peer relationships.
The population studied was Brazilian schoolchildren, which may limit generalizability to other contexts.
The cross-sectional design prevents causal inference about the direction of the associations.
What This Means
This research suggests that how connected Brazilian teenagers are to their peers has a meaningful relationship with how physically active they are in their free time. The study analyzed data from over 100,000 ninth-grade students across Brazil and found that teens who frequently felt lonely were more likely to be completely inactive during leisure time, and teens with no close friends were especially likely to be inactive compared to those with three or more friends. These patterns held even after accounting for other factors like demographics and behaviors.
The study measured physical activity in four categories ranging from zero to 300 or more minutes per week, and it looked at two separate aspects of social life: how often students felt lonely (social isolation) and how many close friends they had (social networks). Both factors were linked to complete inactivity, with having no close friends showing the strongest association — a 69% higher likelihood of being completely inactive compared to students with multiple close friends.
This research suggests that efforts to get teenagers more physically active may need to go beyond just promoting exercise and also consider the social environments of young people. Programs that help adolescents build friendships and feel less isolated could potentially also support more active lifestyles. Because this was a snapshot-in-time study, it cannot confirm whether social isolation causes inactivity, or whether inactive teens become more isolated, but the link between these factors appears substantial.
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Souza R, Cafruni C, Domingues M, Pattussi M. (2026). Social networks, social isolation and leisure-time physical activity in Brazilian adolescent students.. Ciencia & saude coletiva. https://doi.org/10.1590/1413-81232026319.15072024