The World Health Organization (WHO) reports that approximately one in eight people worldwide lives with a mental disorder (World Mental Health Report: Transforming Mental Health for All, 2022), accounting for 32.4% of disability adjusted life years and placing these disorders as the leading cause of years lived with disability worldwide (Vigo et al., 2016). A mental disorder is a syndrome characterized by clinically disturbances in emotion regulation, cognition, or behavior, reflecting underlying dysfunctions in psychological, biological, or developmental processes, with common examples such as anxiety disorders, depressive disorders, schizophrenia, and substance use disorder (American Psychiatric Association, 2013). Among individuals with mental disorders, nearly 70% experience difficulties with sleep onset or maintenance, and more than 30% meet the diagnostic criteria for insomnia disorder (Seow et al., n.d.). Poor sleep quality not only induces short-term cognitive impairment and emotional distress but is also associated with an increased long-term risk of chronic diseases (e.g., diabetes, cardiovascular diseases) and a higher relapse rate of mental disorders (Fang et al., 2019; Medic et al., 2017; Morrison et al., 2022). These adverse effects significantly comprise overall treatment efficacy, undermine health, and diminish productivity ultimately translating into substantial economic costs for both individuals and society (Streatfeild et al., 2021).

Sleep quality is a key indicator for assessing sleep, encompassing both subjective and objective measurements (Crivello et al., 2019; Nelson et al., 2022). Subjective sleep quality indicates a personal experience of how well they sleep, such as feeling rested upon waking or the frequency of nighttime awakenings. This information is typically gathered through questionnaires, rating scales, or sleep diaries. Objective sleep quality is measured using specialized equipment such as polysomnography, which records and analyzes specific metrics like sleep efficiency, sleep onset latency, and duration of wakefulness during the night. Currently, first-line treatment regimens for sleep disturbance rely on pharmacological therapies (such as benzodiazepines and melatonin receptor agonists) and cognitive-behavioral therapy for insomnia (CBT-I) (Pan et al., 2023; Wilkinson et al., 2025). However, individuals with mental disorders are prone to developing tolerance and dependence on sedative medications, and long-term use may exacerbate daytime fatigue and cognitive impairment (Zeraatkar et al., 2025). Despite its proven efficacy, CBT-I faces challenges of scarce professional therapist resources and low patient compliance (Furukawa et al., 2024). Notably, the pathophysiological substrates of mental disorders such as 5-hydroxytryptamine imbalance and HPA axis dysregulation share mechanisms with sleep disorders (Palagini et al., 2019). As such, it is crucial to seek proactive sleep behavior recommendations to optimize sleep quality in individuals with mental disorders.

Exercise, as a form of complementary and alternative therapy, refers to planned, structured, and repetitive physical activity performed to improve or maintain physical fitness (Caspersen et al., 1985). It is widely regarded as a low-risk, cost-effective, and accessible intervention for individuals with mental health conditions. A growing body of evidence supports its significant systemic and multi-organ health benefits in this population (da Cunha et al., 2023; Harvey et al., 2018; Paluska and Schwenk, 2000), leading to its recommendation in clinical guidelines for symptom management (Stubbs et al., 2018; Vancampfort et al., 2025). Furthermore, exercise is commonly employed to improve sleep quality, as it modulates sleep architecture and promotes restorative functions through the regulation of body temperature, hormonal activity, neurotransmitters, and central nervous system responses (Chennaoui et al., 2015). Aerobic exercise, characterized by continuous movement of the body's large muscle groups to improve cardiorespiratory fitness, has been shown in systematic reviews and meta-analyses to significantly improve sleep health—enhancing both subjective sleep quality and objective sleep efficiency—in the general population and other clinical groups (Bu et al., 2025; Kredlow et al., 2015; Yang et al., 2012). However, the efficacy of aerobic exercise specifically for improving sleep quality in people with mental disorders remains equivocal, and existing systematic evidence is inconsistent and incomplete (Brupbacher et al., 2021a, 2021b; Luo et al., 2021). First, previous syntheses have often failed to isolate the effect of aerobic exercise. For instance, while the review by Lederman et al. (2019) found that exercise was associated with improved sleep, it combined aerobic, resistance, mixed, and mind-body modalities, obscuring the unique contribution of aerobic exercise. Second, many reviews are limited to single diagnostic categories (e.g., focusing solely on depressive disorders (Brupbacher et al., 2021a)), preventing generalization across the broader spectrum of mental health conditions. Most critically, prior syntheses have largely treated “exercise” as a uniform intervention, failing to systematically investigate whether and how key exercise prescription parameters (type, intensity, duration, frequency) moderate the effect on sleep—a likely core source of heterogeneity among primary study results. Consequently, there is a lack of a systematic review and meta-analysis that is specifically dedicated to pure aerobic exercise, transdiagnostic in scope, and explicitly designed to quantify the moderating effects of exercise prescription characteristics.

Based on prior research conducted in healthy populations and other clinical groups, we hypothesize that aerobic exercise can significantly improve sleep quality in patients with mental disorders compared with non-exercise control conditions, and we anticipate that the pooled effect size may fall within a small-to-moderate range. To test this hypothesis and clarify the magnitude and direction of the effect, this systematic review aims to 1) systematically evaluate the overall effect of aerobic exercise on sleep quality in patients with mental disorders; 2) explore the moderators that may impact the intervention efficacy of aerobic exercise through subgroup analyses.