Physical activity and mental health: a systematic review and best-evidence synthesis of mediation and moderation studies

Background: While evidence consistently demonstrates that physical activity is beneficial to mental health, it remains relatively unknown how physical activity benefits mental health, and which factors influence the effect of physical activity on mental health. This understanding could vastly increase our capacity to design, recommend, and prescribe physical activity in more optimal ways. The purpose of this study was to systematically review and synthesise evidence of all mediators and moderators of the relationship between physical activity and mental health. Methods: Systematic searches of four databases (i.e., Scopus, PsycINFO, PubMed, and SPORTDiscus) identified 11,633 initial studies. Empirical studies that quantitatively assessed physical activity, or conducted a physical activity intervention, measured a mental health outcome, and tested one or more mediator or moderator of the relationship between physical activity and mental health were included. A total of 247 met the inclusion criteria; 173 studies examined mediation and 82 examined moderation. Results: Results of the best-evidence synthesis revealed strong evidence for 12 mediators including affect, mental health and wellbeing, self-esteem, self-efficacy, physical self-worth, body image satisfaction, resilience, social support, social connection, physical health, pain, and fatigue. Moderate evidence was identified for a further 15 mediators and eight moderators. Conclusions: Findings should inform the design of future physical activity interventions to ensure optimal effects on mental health related outcomes. Additionally, if health professionals were to take these mediators and moderators into consideration when prescribing or recommending physical activity, physical activity would likely have a greater impact on population mental health.