The purpose of this study is to determine whether physical activity prevents development of depressive symptoms in adolescents.

The primary objective of the project is to establish whether increasing physical activity can promote mental well-being in adolescents who are already displaying some depressive symptoms.

A further objective is to evaluate the feasibility of a novel self-motivated physical activity intervention, which has been designed for this project.

The final objective of this project is to investigate alternative intervention delivery modes, for an adolescent sample with subclinical depressive symptomatology, i.e., presenting with some depression symptoms but not at a level where major depressive disorder would be diagnosed. We aim to compare the effect of a completely mediated delivery approach for physical activity (i.e., no researcher contact) and a mediated intervention with face-to-face contact and fortnightly check-in telephone calls.

Inclusion Criteria:

• Adolescents from Grades 7-10 (high school) and their parents/guardians.
• Adolescents scoring in the middle range (14-30) on the Centre for Epidemiological Studies-Depression Scale (possible range 0-60).

Exclusion Criteria:

• Adolescents currently engaging in 60+ minutes of physical activity per day.
• Adolescents who have experienced psychosis, schizophrenia or bipolar disorder.
• Adolescents who score >30 on the CES-D (indicator of severe depression).
• Adolescents who have physical health problems or conditions which preclude them from participation in regular physical activity.
• Lack of written consent from adolescent and/or parent guardian.