The Influence of Presumed Social Media Influence: A Longitudinal Analysis of Social Media Influence on Adolescents’ Physical Activity

Social media plays a central role in adolescents’ lives, suggesting powerful direct and indirect influences on their social norms and behaviors. This study examines these influences by applying the influence of presumed media influence (IPMI) hypotheses to social media and physical activity. Physical inactivity is a pressing public health concern, particularly during adolescence, when activity levels often decline. Using data from a three-wave panel survey (N = 1.044), this study analyzes the development of perceived social media exposure among peers, peer influence, social norms, and personal behavior over time. The findings reveal that social media exposure directly increases physical activity but also via indirect effects proposed by IPMI assumptions. Perceived peer exposure and presumed influence on others strengthened injunctive social norms, resulting in higher physical activity. In contrast, no significant effects were found for descriptive social norms. Therefore, it is important to distinguish between injunctive and descriptive norms. Theoretical and methodological implications for future research and public health interventions are discussed.