IntroductionPersistent psychiatric symptomatology during childhood and adolescence predicts vulnerability to experience mental illness in adulthood. Physical activity is well-known to provide mental health benefits across the lifespan. However, the underlying mechanisms linking physical activity and psychiatric symptoms remain underexplored. In this context, we aim to systematically synthesise evidence focused on the mechanisms through which physical activity might reduce psychiatric symptoms across all ages.Methods and analysisWith the aid of a biomedical information specialist, we will develop a systematic search strategy based on the predetermined research question in the following electronic databases: MEDLINE, Embase, Web of Science, Cochrane and PsycINFO. Two independent reviewers will screen and select studies, extract data and assess the risk of bias. In case of inability to reach a consensus, a third person will be consulted. We will not apply any language restriction, and we will perform a qualitative synthesis of our findings as we anticipate that studies are scarce and heterogeneous.Ethics and disseminationOnly data that have already been published will be included. Then, ethical approval is not required. Findings will be published in a peer-reviewed journal and presented at conferences. Additionally, we will communicate our findings to healthcare providers and other sections of society (eg, through regular channels, including social media).PROSPERO registration numberCRD42021239440.

Background: Physical activity has been suggested as a protective factor against psychiatric symptoms. While numerous studies have focused on the magnitude of the effect of physical activity on psychiatric symptoms, few have examined the potential mechanisms. Objective: The current review aimed to synthesize scientific evidence of the mechanisms through which physical activity might reduce psychiatric symptoms across the lifespan. Methods: We included articles that were published before March 2022 from five electronic databases (Medline, Web of Science, PsycINFO, Embase, and Cochrane). A qualitative synthesis of studies was conducted. The risk of bias assessment was performed using The Joanna Briggs Institute Critical Appraisal Tool for Systematic Reviews. Studies were included if they explored the possible mechanisms through which physical activity links with psychiatric symptoms (i.e., internalizing and externalizing symptoms) across the lifespan. Results: A total of 24 articles were included (three RCTs, four non-RCTs, four prospective longitudinal studies, and 13 cross-sectional studies). Overall, most of the studies (70%) focused on children, adolescents, and young adults. Our findings show that self-esteem, self-concept, and self-efficacy were the only consistent paths through which physical activity may influence psychiatric symptoms (specifically depressive and anxiety symptoms). There were insufficient studies to determine the role of neurobiological and behavioral mechanisms. Findings from our systematic review suggest that self-esteem, self-concept, and self-efficacy are potential paths through which physical activity might reduce psychiatric symptoms across the lifespan. Conclusions: Overall, future physical activity interventions with the purpose of improving mental health should consider these mechanisms to develop more effective interventions. Current literature gaps and recommendations for researchers to explore other potential mechanisms were also included. Protocol Registration: The protocol of this study was registered in the PROSPERO database (registration number CRD42021239440) and published in April 2022. Keywords: exercise, psychiatric symptom, mechanism, neurobiological, behavioral, longevity, self-concept, self-esteem, self-efficacy, psychosocial, mental disorders

Introduction: Persistent psychiatric symptomatology during childhood and adolescence predicts vulnerability to experience mental illness in adulthood. Physical activity is well-known to provide mental health benefits across the lifespan. However, the underlying mechanisms linking physical activity and psychiatric symptoms remain underexplored. In this context, we aim to systematically synthesize evidence focused on the mechanisms through which physical activity might reduce psychiatric symptoms across all ages. Methods and analysis: With the aid of a biomedical information specialist, we will develop a systematic search strategy based on the predetermined research question in the following electronic databases: MEDLINE, Embase, Web of Science, Cochrane, and PsycINFO. Two independent reviewers will screen and select studies, extract data, and assess the risk of bias. In case of inability to reach a consensus, a third person will be consulted. We will not apply any language restriction, and we will perform a qualitative synthesis of our findings as we anticipate that studies are scarce and heterogeneous. Ethics and dissemination: Only data that has already been published will be included. Then, ethical approval is not required. Findings will be published in a peer-reviewed journal and presented at conferences. Additionally, we will communicate our findings to healthcare providers and other sections of society (e.g., through regular channels, including social media). PROSPERO registration number: CRD42021239440