Abstract
Introduction: Physical activity is known to have positive effects on physical health, but evidence on its relationship with mental health in low- and middle-income countries, particularly among adolescents, remains limited. This study examined the association between physical activity and depressive symptoms among adolescents in Ondo State, Nigeria, and assessed the effect of a structured physical activity intervention.

Methods: The study was a quasi-experimental design conducted in two phases: a cross-sectional survey followed by an intervention phase. The survey involved 277 students recruited between March and April 2020 from two secondary schools in Akure, Ondo State, Nigeria. Participants completed a sociodemographic questionnaire, the Short Mood and Feelings Questionnaire (SMFQ), and the Physical Activity Questionnaire for Adolescents. For the intervention phase, 40 students who scored ≥11 on the SMFQ were selected to participate in the intervention (six-week physical activity programme) or a control group, on the wait-list, with no intervention. Outcome measures were reassessed at six weeks.

Results: The prevalence of significant depressive symptoms was 17.7%. Higher physical activity levels were associated with lower depressive symptoms (r = −0.15, p = 0.01) and the treatment group had significantly lower depression scores compared with the control group (t= -2.78, p=0.009) post intervention. ANCOVA showed a significant effect of the treatment on the intervention group as measured by the SMFQ {F (1, 34) = 7.05, p= 0.01}.

Conclusion: This study found that structured physical activity was associated with a greater reduction in depressive symptoms among adolescents in the intervention group compared with controls. Integrating structured physical activity into school routines can support mental health and well-being.

Key words: Adolescent, Depression, Physical Activity, Intervention, Nigeria