Article Contents
30 min read

Abstract 1. Introduction 2. Literature Review 3. Methods 4. Results 5. Discussion 6. Limitations 7. Future Directions 8. Conclusion 9. References

Abstract

Background 

Depression is a prevalent and debilitating disorder impacting over 300 million individuals globally. Traditional treatments include psychotherapy and antidepressant medications; However, these methods often fall short due to high costs, adverse side effects, and suboptimal remission rates. Consequently, there is a growing need for alternative treatment options. Exercise is recognized by various health guidelines as a potential supplementary treatment for non-severe depression, yet the evidence supporting its efficacy remains inconsistent.  

Methods 

A systematic review was conducted following PRISMA guidelines. The review focused on RCTs published between 2011 and 2024, evaluating the effects of exercise interventions on depressive symptoms. Studies included adults diagnosed with depression using validated screening measures, excluding those involving mind-body exercises like tai chi or yoga. The primary outcome was a change in depressive symptoms, assessed using validated scales such as the Beck Depression Inventory and the Hamilton Rating Scale for Depression (HAM-D).

Results 

Eight RCTs met the inclusion criteria, encompassing a range of exercise interventions and durations. The review revealed that short-duration exercise interventions (8-12 weeks) consistently resulted in significant improvements in depressive symptoms compared to longer-duration studies (24 weeks). Light to vigorous exercises were effective in reducing depression severity, and self-selected intensity exercises showed particularly promising results in enhancing adherence and outcomes. However, variations in control group activities and the nature of the exercise prescribed often introduce confounding factors. 

Conclusion 

The findings support the efficacy of exercise as an adjunct treatment for depression, particularly for short-term intervention. Despite the methodological challenges and variability in study designs, exercise demonstrates significant potential in improving depressive symptoms. Future research should aim to standardize intervention protocols and control conditions, include long-term follow-up periods, and explore tailored exercise prescriptions to optimize treatment outcomes. The review underscores the importance of incorporating exercise into treatment plans for depression to enhance overall well-being.

Introduction

Depression is a common and disabling disorder that significantly reduces quality of life and is associated with medical comorbidities and increased mortality1,2. Over 300 million people worldwide are affected by depressive disorder3. Currently, psychotherapy and antidepressant medications, either alone or in combination, are the recommended treatments for depression4. However, psychotherapy achieves remission in only about 50% of cases and is typically expensive5. Antidepressant medications frequently lead to side effects, relapses, and withdrawal symptoms6. One serious side effect linked to antidepressants is suicide, with an increased risk of suicidal behavior in adults, suggesting careful monitoring during treatment7. Another significant issue with antidepressants is that a substantial number of patients discontinue their medication within the first six months and varying adherence rates with a median of 63% 8,9. Notably, around 70% of adults with depression do not receive adequate treatment10. Untreated depression can lead to the worsening of the illness and the development of comorbidities, resulting in increased costs for society11,12. This emphasizes the need for easily accessible alternative treatment options13.

Several guidelines, including those from the European Psychiatric Association (EPA), the National Institute for Health and Care Excellence (NICE), and the World Health Organization (WHO), endorse exercise as an alternative treatment for non-severe depression4,14,15. In contrast, the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) only recommends exercise when antidepressants or psychotherapy are ineffective or unacceptable and states there is insufficient evidence to support it as an official treatment16. This discrepancy highlights the difficulty in drawing definitive conclusions about the role of exercise in treating non-severe depression 17. This systematic review aims to examine the impact of exercise on depression. 

Literature Review

The World Health Organization (WHO) guidelines recommend exercise as an adjunct treatment for non-severe depression14. This recommendation is supported by evidence from various meta-analyses that have examined the antidepressant effects of exercise in individuals with depression. However, these meta-analyses have produced mixed results. Some found moderate, weak, or no effects of exercise18,19, while others reported significant effects20-22. These discrepancies arise from methodological and conceptual differences, such as varying inclusion criteria and analytical approaches13. 

For instance, some studies focused on individuals diagnosed with major depressive disorder (MDD) and emphasized clinical assessments of MDD rather than solely relying on validated screening measures18. Others examined the effects of exercise either independently or as an adjunct to pharmacological therapy20. Additionally, some reviews included studies where control groups also received exercise interventions19, potentially introducing bias, as even light-intensity exercise can have antidepressant effects13.

Numerous reviews have expressed concerns that the effectiveness of exercise diminishes when analyses are confined to randomized controlled trials (RCTs) with ‘low risk of bias’. For instance, when these reviews utilized the Cochrane risk of bias assessment tool, they only included studies meeting rigorous standards for minimizing potential bias. This exclusion of studies with moderate or high risk of bias led to the findings that the effects of exercise on depression were much lower when only low-risk studies were considered. As a result, current meta-analyses have failed to offer definitive evidence for clinicians to universally endorse exercise as an evidence-based treatment for depression18,19. 

Recent systematic reviews, including those by Noetel et al. and Recchia et al. have further illuminated the benefits of exercise as an intervention. Recchia et al. found no difference between exercise and pharmacological interventions in reducing depressive symptoms in adults with non-severe depression17. Noetel et al. underscore that different modalities and intensities of exercise can positively impact depression. Moreover, exercise provides holistic benefits, impacting not just physical health but also social, psychological, and neurobiological aspects, making it a comprehensive treatment approach23. 

Exercise intensity can be categorized into several levels, typically described as light, moderate, and vigorous. These intensities are measured using various physiological and subjective methods24. Light-intensity activities do not significantly elevate heart rate (HR) or breathing, such as walking slowly or doing yoga. Moderate-intensity activities elevate heart rate and breathing but allow for conversation. Examples include cycling at a moderate pace and brisk walking. Vigorous intensity exercises significantly elevate heart rate and breathing, making conversation difficult. Examples include running and high-intensity interval training (HIT)24. Light-intensity activities typically use less than 3.0 METs (metabolic equivalents), moderate-intensity activities use 3.0-6.0 METs, and vigorous-intensity activities use more than 6.0 METs. For instance, brisk walking at 4mph is considered moderate-intensity, while jogging at 6 mph is vigorous-intensity25,26. Measuring exercise intensity can also involve heart rate monitoring, where according to ACSM’s guidelines, moderate intensity is 64-76% of maximum heart rate, and vigorous intensity is 77-95%.24 

Additionally, the Borg Rating of Perceived Exertion (RPE)27 scale is a subjective method to measure exercise intensity based on individual perception of effort, breathlessness, and fatigue during physical activity. The Borg scale ranges from 6-20, with 6 being “no exertion at all” and 20 being “maximal exertion.” Moderate-intensity exercises typically fall between 11-14 on the Borg scale, while vigorous-intensity exercise usually rates 15 or higher on the Borg scale. One issue with categorizing exercise intensity is that it encompasses a wide and heterogeneous spectrum of ranges and definitions, which can lead to inconsistencies and difficulties when comparing studies28. Self-selected exercise intensity can significantly improve adherence to exercise programs29. Individuals who choose their exercise intensity are more likely to engage consistently and sustain their participation. This approach aligns with their preferences and capabilities, making the exercise experience more enjoyable and less taxing, which reduces dropout rates. By catering to personal comfort and motivation levels, self-selected exercise intensity helps maintain long-term commitment, leading to better mental health outcomes and overall well-being29. 

Our systematic review aims to update and expand upon previous analyses by incorporating recent studies and addressing past methodological limitations. We will focus on randomized controlled trials that assess the antidepressant effects of exercise, comparing active exercise interventions to non-active controls and accounting for potential biases. By doing so, we hope to provide clearer guidance for clinicians considering exercise as a treatment option for depression. 

Methods

Eligibility criteria  

This systematic review adhered to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) Statement guidelines30. The eligibility criteria were structured using the PICOS (Patient/Population; Intervention; Comparison; Outcome; Study Design) framework31. 

Participants 

Studies eligible for the systematic review included studies that examined adults with depressive symptoms determined by validated screening measures above the threshold value for example, the Beck Depression Inventory(BDI) or Hamilton Rating Scale for Depression(HAM-D))32,33. In cases where the scales lacked validated cut-offs, the cut-off points determined by the original authors were utilized. 

Intervention 

We defined exercise according to the American College of Sports Medicine guidelines as ‘planned structured and repetitive bodily movement aimed to improve and/or maintain one or more components of physical fitness’25. Eligible interventions included aerobic exercises (e.g., walking, running, cycling) and/or anaerobic exercises (e.g., resistance training, strength exercises, weight lifting). Studies involving mind and body exercises, such as tai chi, qigong, yoga, etc, were excluded34. It is important to differentiate between these mind-body exercises because they generally incorporate a focus of the mind on the body and breathing to achieve deep states of relaxation. This distinct feature is a primary mechanism through which they impact health, making them different from typical physical exercise that primarily aims to enhance physical fitness through cardiovascular or muscular exertion34. We also excluded studies that only provided guided exercise without a structured exercise program. 

Comparators 

The control group has the option to receive a placebo, standard care, or an alternative treatment such as antidepressant medication, psychotherapy, or other interventions. Studies were excluded if the control group was prescribed exercise, to avoid bias from exercise effects. 

Outcomes 

Eligible studies had to examine the pre-post effects of exercise interventions on depressive symptoms using a validated depression scale. The primary or secondary outcome measure had to be symptoms of depression, assessed with a validated scale on depression severity such as BDI or HAM-D with numeric data reported. 

Study Design 

Only randomized controlled trials (RCTs) published in peer-reviewed journals in English were included. Studies focusing on the immediate effects of exercise, those with exercise programs lasting less than eight weeks, and those without non-exercising control groups were excluded. 

Literature search 

Our searches covered articles published in PubMed from 2011 to 2024. The search strategy included the following terms and Boolean operators: “usual care" OR "treatment as usual" AND depression AND exercise. Filters were applied to include only randomized controlled trials (RCTs) published in English, and the publication dates were restricted to studies published between 2011 and 2024. 

Study selection, Data Extraction and Quality Assessment  

The author of the paper evaluated the full-text articles based on the eligibility criteria. After obtaining the full texts, the reviewer applied the eligibility criteria and generated a final list of included studies. Data were extracted using a standardized form, including information on study characteristics, participant demographics, intervention details, and outcomes. The PRISMA flowchart in Figure 1 was made using Covidence and outlines the study selection process, including the number of individuals identified, screened, assessed for eligibility, and included in the review. 

Results

The characteristics of the included randomized controlled trials (RCTs) assessing the effects of exercise on depressive symptoms are summarized in Table 1. This table provides detailed information on study reference, participants, severity of depression at baseline, intervention, frequency of exercise, intervention duration, depression assessment tools, main outcomes, whether the intervention was adjunct or standalone, intensity of exercise, and unique contributions of each study. Overall, approximately 75% of the included studies reported significant improvements in depressive symptoms with exercise interventions, particularly those with short-duration interventions (8-12 weeks).

6-Month Studies 

Kruisdijk et al. (2012) conducted a randomized controlled trial (RCT) to evaluate the effects of running therapy on depression in 183 patients with Major Depressive Disorder (MDD). High dropout rates limited the analysis to 46 participants (24 in the intervention group). The results indicated that HAM-D17 scores showed an average reduction of 2-3 points in the intervention group after three months compared to the control group. However, the General Linear Model (GLM) analysis showed no significant effect on depression (Cohen’s d < 0.2, F = 0.13, p = 0.73). The study suggested that an integrated lifestyle intervention might be more effective than a single add-on exercise intervention35. 

Ridsdale et al. (2012) conducted an RCT to examine the effectiveness of graded exercise therapy (GET), counseling (COUNS), and usual care plus a cognitive behavior therapy (CBT) booklet (BUC) for individuals with chronic fatigue. The study involved 222 participants aged 16 to 75. Secondary outcomes included changes in depression and anxiety levels, assessed using the Hospital Anxiety and Depression Scale (HADS). All three groups (BUC, GET, COUNS) showed reductions in HADS depression scores from baseline to the six-month assessment, with no significant differences between the groups in terms of depression score changes at six or twelve months. The study concluded that GET and COUNS were equally effective as BUC in reducing depression symptoms in individuals with chronic fatigue36. 

Sari et al. (2019) conducted an RCT to evaluate the effects of exercise as an adjunctive treatment on the quality of life of individuals with alcohol use disorders. The study included 117 participants recruited from an alcohol outpatient treatment center in Denmark. Participants were aged 18 years or older, fulfilled ICD-10 criteria for harmful use of or dependence on alcohol, and were randomly assigned to one of three groups: treatment as usual (TAU, n=36), TAU with supervised group exercise (n=41), or TAU with individual exercise (n=40). The primary outcome measure was quality of life, which was, assessed using the EuroQOL five dimensions questionnaire (EQ-5D) and the visual analog scale (EQ-VAS), measured at baseline and six months post-treatment. Although not statistically significant, a larger portion of the individual exercise group reported no pain or discomfort (62%) compared to the control group (38%) at follow-up (p = 0.078). There were no significant differences in self-rated health status between the groups at follow-up. The study suggested that exercise could potentially reduce pain and discomfort, warranting further research37. 

 Studies with Other Durations 

Helgadóttir et al. (2016) investigated the effects of different exercise intensities on depression severity in 620 participants aged 18-67 with mild to moderate depression. The study included 4 groups: treatment as usual (TAU) (n=310), light exercise (n=106), moderate exercise (n=105) , and vigorous exercise (n=99). The results showed that all exercise groups significantly reduced their MADRS scores compared to TAU at post-treatment. Light exercise reduced MADRS scores by -4.05 (-5.94, -2.17), moderate exercise by -2.08 (-3.98, -0.18), and vigorous exercise by -3.13 (-5.07, -1.19). All exercise intensities showed significant reduction in depression indicating various exercise intensities may be beneficial for individuals with mild to moderate depression38. 

Helgadóttir et al. (2017) examined the long-term effects of exercise at different intensity levels in 620 participants aged 18-67 with mild to moderate depression. Light exercise significantly reduced depression severity at the 12-month follow-up compared to TAU (-1.9, 95% CI: -3.7, -0.04) and moderate exercise (-2.94, 95% CI: -5.2, -0.7). Vigorous exercise was also more effective than moderate exercise (-2.7, 95% CI: -4.9, -0.4). Effect sizes were as follows: light exercise (Hedges’ g = 0.57, 95% CI: 0.34, 0.79), moderate exercise (Hedges’ g = 0.31, 95% CI: 0.09, 0.53), and vigorous exercise (Hedges’ g = 0.45, 95% CI: 0.23, 0.68). These findings suggest prescribing light exercise may be particularly beneficial for individuals with mild to moderate depression39. 

Doose et al. (2015) conducted an RCT with 46 outpatients to evaluate self-selected intensity aerobic exercise. The intervention group showed a significant reduction in HRSD-17 scores (Cohen’s d: 1.8; mean change: 8.2, p < .0001) and a moderate, non-significant reduction in BDI-II scores (Cohen’s d: 0.50; mean change: 4.7,p = 0.09). The study concluded that self-selected intensity aerobic exercise significantly reduced depression severity as measured by HRSD-17 40. 

Hallgren et al. (2015) compared physical exercise, internet-based cognitive-behavioral therapy (ICBT), and treatment as usual (TAU) in 946 participants. Both physical exercise and ICBT showed significant reductions in MADRS scores compared to TAU (mean difference: 2.99, 95% CI: 1.61–4.37 for exercise; 2.83, 95% CI: 1.47–4.19 for ICBT; p < 0.001 for both). The study supported the use of physical exercise and ICBT as effective treatments for mild to moderate depression41. 

Sturm et al. (2012) conducted a randomized controlled crossover trial to examine the effects of mountain hiking on depression in high-risk suicide patients. The study included 20 participants who had previously attempted suicide and were clinically diagnosed with hopelessness. The primary outcome measures were changes in depression, hopelessness, and suicide ideation, assessed using the Beck Depression Inventory (BDI)33, Beck Hopelessness Scale (BHS)42, and Beck Scale for Suicide Ideation (BSI)43. Participants were randomly assigned to one of two groups. Group 1 (n=10) began with a 9-week hiking phase followed by a 9-week control phase. Group 2 (n=10) underwent the phases in reverse order. The hiking program included three hikes per week, each lasting 2-3 hours, conducted at 65-75% of the participant's maximum heart rate, monitored using heart rate monitors, with warm-up and cool-down exercises before and after hikes. The results indicated a significant reduction in depression during the hiking phase (P < 0.0001, Cohen’s d = 1.38), with an increase in depression scores during the control phase (P = 0.04, Cohen’s d = 0.54). Hopelessness significantly decreased during the hiking phase (P < 0.0001, Cohen’s d = 1.4), with no significant change during the control phase. Suicide ideation significantly reduced within the hiking phase (P = 0.005, Cohen’s d = 0.79), but there was no significant effect when comparing the hiking and control phases overall (P = 0.25, Cohen’s d = 0.29). The study concluded that regular mountain hiking significantly reduced depression and hopelessness in high-risk suicide patients, suggesting it can be an effective adjunct to usual care44. 

The overall pattern in our systematic review suggests that six-month interventions may not always show significant direct effects on depressive symptoms. Some possible confounding factors include the frequency of exercise, which was consistently 2 sessions per week for the 24-week studies and 3 sessions per week for four of the shorter-duration studies, with one study exercising for 2-3 times per week.

Discussion 

The current systematic review reinforces the WHO recommendation of exercise as a supplementary treatment for depression14. Despite the mixed results in meta-analyses, there is a consensus that exercise can have significant antidepressant effects under certain conditions. Methodological differences, such as inclusion criteria and analytical approaches, contribute to the variability in findings across studies. Research by Ekkekakis et al. suggests that the impact of exercise on depression might be greater than previously reported45.

To address these methodological concerns one meta-analysis18 emphasized studies that included participants with depression diagnosed using validated screening instruments and MDD diagnoses confirmed with validated diagnostic tools. It included only studies comparing exercise to non-active controls and excluded trials comparing different exercise regimens. Despite these improvements, many new studies have been published since then, necessitating an updated meta-analysis to assess the antidepressant effects of exercise while addressing the limitations of previous reviews. 

Several reviews have raised concerns about the effectiveness of exercise interventions when limited to ‘low risk of bias’ randomized controlled trials (RCTs)18,19. This review addressed these concerns by including studies with validated screening instruments and more homogeneous populations to reduce bias. The current researcher found that exercise interventions can be effective, but the variability in control group activities and the nature of the exercise prescribed often introduce confounding factors. Notably, the use of data from the Regassa project in multiple studies (Helgadóttir 2016, Helgadóttir 2017, Hallgren 2015) could be a confounding factor to the observed patterns of significance. This shared data set might lead to consistent findings within those studies but limit the generalizability of the results. 

Using participants with similar symptoms and consistent responses to exercise interventions can minimize within-group variance and enhance the observed effect sizes. However, depression is a heterogeneous disorder46,47 with a wide range of symptoms, such as psychomotor changes, appetite fluctuations, and sleep disturbances. Therefore, individuals with identical depression scores might present with different symptom profiles45,47,48. The heterogeneity of depressive symptoms may indicate differences in underlying neurobiological processes46,48, suggesting that a uniform exercise prescription may not be equally effective for all patients. This variability involves various biopsychosocial factors. For instance, recent evidence suggests that clinical factors such as the severity of somatic symptoms, biological markers like brain-derived neurotrophic factor (BDNF) and tumor necrosis-alpha, psychological factors like self-esteem and life satisfaction, and social factors like support and marital status, may influence the antidepressant effects of exercise49. Recent studies indicate that creating a typology to align specific types of depression with tailored exercise prescriptions could greatly benefit both research and clinical practices, enhancing the effectiveness of treatment strategies45,47,48. 

In understanding the impact of exercise on depression, it is essential to consider the underlying hypothetical mechanisms, moderators, and confounders. An exemplary diagram of potential mechanisms, moderators, and confounders is presented in the paper by Kandola et al.50,which offers a thorough overview of these proposed interactions. Several review papers have explored these potential mechanisms and their moderators, providing insights into how exercise might influence mental health through biological and psychosocial pathways49,51. By examining these hypothetical factors, we can better understand the multifaceted benefits of exercise and how different variables may moderate its effects on depression.  

Hypothetical Biological Mechanisms 

Neurotransmitters: Exercise is believed to impact mental health by affecting levels of neurotransmitters such as serotonin, dopamine, and norepinephrine52, which are involved in mood regulation. The monoamine hypothesis53 suggests that these changes contribute to mood improvement and reduced depressive symptoms. 

Neurotrophins: Recent evidence suggests that biological markers like brain-derived neurotrophic factor (BDNF)54,55 may influence the antidepressant effects of exercise. These neurotrophins stimulate the growth of new neurons and enhance synaptic plasticity, promoting better mental health56,57.

Neuromodulators: The endorphin hypothesis58 posits that exercise increases the release of endorphins, natural opioids that can induce feelings of euphoria and reduce pain. However, recent studies suggest endocannabinoids may play a larger role59, highlighting the endocannabinoid hypothesis, which emphasizes the role of exercise-induced endocannabinoid production in mood improvement and stress reduction59-61. 

Thermogenic hypothesis: The thermogenic hypothesis suggests that the increase in body temperature from exercise may lead to reductions in muscle tension and changes in the central nervous system, improving mood and reducing anxiety62. However, this hypothesis has been largely unsupported, as several studies have failed to establish a direct link between elevated body temperature from exercise and significant mood improvements, suggesting other mechanisms may play a more critical role in the antidepressant effects of exercise63. 

Hypothetical Psychosocial Mechanisms 

Self-Efficacy: Self-efficacy is the confidence in one’s ability to perform a specific task within a given context64. It embodies the belief that an individual can successfully execute the actions required to achieve goals. The improvement of self-efficacy hypothesis suggests that exercise enhances self-efficacy, leading to improved mood and reduced depressive symptoms64-66. This can be achieved through skill mastery, developing a transferable sense of coping with challenges and increasing barrier self-efficacy50,67,68. 

Social Support: Exercise often involves social interactions, providing more opportunities for emotional disclosure and exposure to new social networks. Social support, which includes assistance from social relationships and interactions69 can contribute to improved mental health by reducing feelings of isolation and promoting a sense of belonging. Individuals with depression frequently report inadequate social support70, while sufficient social support can protect against depression50,71. 

Self Esteem: Regular exercise can improve self-esteem by promoting a positive self-image and increasing physical fitness, which can contribute to better mental health outcomes49,72. 

Distraction from Negative thoughts: The distraction hypothesis proposes that exercise provides a distraction from negative thoughts and rumination, contributing to mood improvement73. By focusing on physical activity, individuals may experience temporary relief from depressive symptoms51. 

These biological and psychological mechanisms underscore the multifaceted benefits of exercise in treating depression. Nonetheless, insufficient evidence exists to validate or disprove most of these theories74. Future research should aim to delineate these pathways more clearly, exploring how different types of exercise influence specific neurobiological and psychological factors. 

Limitations 

One limitation of the current systematic review is that we were only able to review publications in English. This language restriction could result in the exclusion of relevant studies published in other languages, potentially leading to bias in our findings. 

A significant challenge encountered during the review was the inconsistent definitions and descriptions of "treatment as usual" (TAU) and "usual care" (UC) across the included studies. This inconsistency is a common issue in the field, as TAU is often insufficiently described in RCTs75 The lack of standardized descriptions can affect the interpretation of results and the ability to compare outcomes across studies. According to Petersson et al. (2023), TAU descriptions in primary care research can be classified into three levels: basic, moderate, and advanced. Basic descriptions lack detailed accounts and references to guidelines; moderate descriptions include references to guidelines or detailed descriptions, and advanced descriptions provide comprehensive details, including references to national guidelines and key treatment components such as early assessment, accessibility, psychological treatment, medication, and somatic examination75. These variations can lead to difficulties in drawing definitive conclusions about the efficacy of exercise interventions for depression. The authors recommended that authors conducting research in primary care define TAU according to the advanced level to mitigate heterogeneity in mental health studies due to inconsistent descriptions of TAU. 

High dropout rates in some studies limited the statistical power via a smaller sample size and the ability to generalize the findings due to attribution bias. For instance, Kruisdijk et al. (2019) experienced high dropout rates, resulting in only 46 participants being analyzed from an initial 183. Many studies in the review may have selection bias, as participants often volunteered for exercise interventions. This may not represent the broader population with depression, as volunteers might be more motivated or have different characteristics than non-volunteers. 

40Moreover, some studies had relatively short follow-up periods, limiting the ability to assess the long-term effects of exercise on depression. Longer follow-up periods are necessary to determine the sustained benefits of exercise interventions. 39-41,44Several studies had small sample sizes, which reduces the power to detect significant effects and increases the risk of Type II errors. Larger sample sizes are needed to confirm the findings and provide more robust evidence40,44.  

Control conditions varied across studies, with some using usual care, others using wait-list controls, and others using different forms of intervention. This inconsistency makes it difficult to compare results directly and determine the true efficacy of exercise interventions. Furthermore, the effects observed in the studies could be influenced by confounding factors such as social support, treatment expectations, and other psychosocial variables that were not controlled for in the study designs. 

Commonly used outcome measures, like the Hamilton Rating Scale for Depression, have several psychometric issues, including a lack of unidimensionality and poor ability to detect changes in individuals with mild to moderate depressive symptoms76,77. These issues are particularly relevant for studies examining the antidepressant effects of exercise, as exercise is often recommended for those with mild to moderate symptoms. As a result, the Hamilton scale might not precisely indicate the full antidepressant impact of exercise. For future research, it is advisable to use newer scales based on DSM-IV criteria, like the Inventory of Depressive Symptoms, which more effectively measure variations in symptom severity45,78. 

Future Directions 

Future research should address these limitations by standardizing the descriptions of control conditions (TAU/UC) and utilizing more recent and validated depression scales. For example, the Inventory of Depressive Symptomatology (IDS), based on DSM-IV criteria, is recommended as it better captures changes across all levels of symptom severity compared to traditional scales like the Hamilton Rating Scale for Depression (HAM-D)45,78. Implementing these standardized measures will enhance the comparability and reliability of study results, facilitating more accurate assessments of the antidepressant effects of exercise. 

Additionally, future research should aim to include studies with long-term follow-up and detailed descriptions of exercise characteristics better to understand the sustained effects of exercise on depression. These descriptions should encompass the frequency, intensity, duration, and dosage, as well as whether the exercise is performed in a group or individual setting, supervised versus unsupervised, the progression intensity over time, the setting, and the specific type of exercise(e.g., aerobic, resistance, etc.). By specifying these characteristics, researchers can better understand the sustained effects of different exercise regimens on depression. 

Replicating these findings in diverse populations and settings will further validate the benefits of exercise for depression. By addressing these factors, future research can provide more definitive evidence on the long-term benefits of exercise for depression, ultimately improving the quality of life for those affected by debilitating conditions. 

A significant challenge in the application of exercise prescriptions for depression lies in the low motivation levels observed in a substantial subset of patients. Addressing this issue necessitates innovative approaches to enhance patient engagement. Evidence suggests that integrating mobile app support79, implementing behavioral activation strategies80, and promoting group and supervised81 exercise sessions can significantly bolster motivation and adherence. Furthermore, for individuals with severe depression, current clinical guidelines advocate the initiation of treatment with antidepressant medications prior to introducing exercise regimens as a supplementary therapy82. 

Conclusion 

This systematic review provides moderate evidence supporting the use of exercise as a supplementary treatment for depression. Shorter-duration studies (8-12 weeks) consistently show significant improvements in depressive symptoms compared to longer-duration studies (24 weeks), likely due to higher adherence and lower dropout rates. Variability in exercise intensity, frequency, and the type of control groups may influence this discrepancy. 

Despite these challenges, the potential benefits of exercise for individuals with depression are significant. Exercise interventions, whether used as an adjunct to UC/TAU or as a standalone treatment, can offer a non-pharmacological option that can improve mental health outcomes. However, the effectiveness of these interventions depends on several factors, including the type, intensity, and frequency of exercise and the level of supervision and support provided to participants. Future research should aim to standardize intervention protocols and descriptions of control conditions to enhance comparability across studies. Additionally, incorporating more recent and validated depression scales, such as the Inventory of Depressive Symptomatology (IDS), can provide more accurate assessments of the antidepressant effects of exercise. 

In conclusion, while challenges remain, the potential for exercise to serve as a critical component in the management of depression is evident. With continued research and careful implementation, exercise can play a crucial role in improving mental health and enhancing the overall well-being of individuals with depression. 

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