INTRODUCTION

Depression is considered a mental disorder that is characterized by the manifestation of depressive episodes once or twice a week. These episodes are expressed by the loss of interest and pleasure in activities of daily living (ADL). Persistent mood changes associated with emotional, cognitive and behavioral symptoms translating into loss of self-esteem, feelings of guilt and incapacity¹.

Depression is a prevalent disease throughout life that affects 10 to 20% of the population in different countries, being the main responsible for the disability caused by mental disorders and substance use (about 40.5% of the total years of life adjusted for disability)².

People with depression, in many cases, have associated comorbidities, increasing the negative impact on their quality of life, not only in social activities and ADL, but also in the increase in hospitalizations and mortality³.

In order to counteract depressive symptoms, there is a growing need to find strategies and therapies that make it possible to reduce these symptoms. In this sense, the use of non-drug therapies, such as physical exercise, can have a positive effect on decreasing depressive symptoms. This is well tolerated by people with depressive disorder, with good adherence, but it has to be administered, prescribed, managed supported and/or carried out by health professionals with specific training in exercise prescription⁴. Physical exercise is understood as the planned, organized and repeated body movements in order to maintain or improve one or more components of physical fitness⁵. There is evidence that physical exercise is an adjunct to the treatment of major depressive disorder, with beneficial effects in people ⁶. Thus, with the systematic literature review (SLR), we intend to find an answer to the following question: what are the benefits of physical exercise for people with depression?

Thus, it is intended to identify the benefits of physical exercise for people with depression.

MATERIAL AND METHODS

A literature review aims to systematize the studies of clinical practice in health care, which can be expressed in various ways. SLR is defined as an investigation method focused on a clearly formulated question, which, through systematic, explicit and reproducible methods, allows the identification, evaluation and synthesis of studies with relevant evidence. This is carried out by researchers, academics and health professionals, allowing the collection and analysis of data from the studies that are included in the review⁷.

For the present study, an SLR to publications worldwide was carried out between January 2014 and November 2018.

The recommendations of the Joanna Briggs Institute (JBI) were considered, which resulted in the research question from the PICO strategy^8-10, the research question was formulated “What are the benefits (O) of physical exercise (I) in the person with depressive disorder (P) compared to the control group (C)?” where each PICO dimension contributed to define the inclusion criteria: Population (P) - People with depressive disorder; Intervention (I) - physical exercise, and Comparison (C) - people with depression who do not exercise compared to a group of people with depressive disorder who are subject to complementary therapy, exercise, and Results (O) - benefits of physical exercise in people with depressive disorder.

The descriptors related to each of the components of the PICO strategy were previously validated in the Descriptors in Health Sciences and Medical Subject Headings platform. The following Keywords were also used: exercise training, physical activity, and depressive disorder.

The following were defined as inclusion criteria for articles: (Table 1) quantitative studies, published in the last 4 years (2014-2018), in Portuguese, English and Spanish, with accessible full text.

The research was carried out by four investigators simultaneously, in the period between October and November 2018, and for it the following databases were used: EBSCOHost and online library B-on.

The articles selected for full reading were independently evaluated by two investigators, according to methodological quality criteria proposed by the JBI⁸, with only articles with more than 75% of the criteria being selected.

Information was extracted from the articles on authors, year, country, sample, data on the intervention (frequency, intensity, volume, duration and modality), conclusions and level of evidence. The classification of the levels of evidence of the included studies was based on the criteria of the Registered Nurses Association of Ontario^9,11.

RESULTS

From the bibliographic research process carried out with this methodology, on the EBSCOhost platform we obtained 1,138 articles for initial selection. After insertion of the inclusion criteria, 156 articles were found. Out of these, 117 were rejected by title or subject and 33 by abstract. Out of the 6 resulting articles, all were excluded after analysis of the full text, as they did not meet the defined inclusion criteria.

By replicating the same methodology on the B-on platform, 1,967 articles were found, of which 702 articles were selected after insertion of the inclusion criteria. Of these, 658 were rejected by title or subject and 31 by abstract. Of the 13 resulting, 4 were excluded after reading the entire text, as they did not meet the defined inclusion criteria. As a final result, 9 articles that meet the inclusion criteria were obtained.

Table 2 describes the process of combining descriptors and keywords for searching the databases. Figure 1 illustrates the PRISMA¹² flowchart corresponding to the identification, analysis, selection and inclusion of articles.

Figure 1 Identification, analysis and selection of articles ⁽¹² . ⁾  

In summary, 9 articles were included in this SLR that were published from 2015 to 2018.

The sample of people/participants in the different studies ranged between 14¹⁷ and 310²¹ and for the control group, the number of participants ranged between 6¹⁷ and 310²¹. All studies included (table 2) are descriptive studies, with evidence level IB, that is, evidence obtained from a well-designed study, and from at least one randomized controlled study ^10-11 (Table 3).

DISCUSSION

In order to understand the benefits of physical exercise in people with depressive disorder, we analyzed different studies in which a variety of strategies were found, such as the use of physical exercise and/or cognitive-behavioral therapies to reduce depressive symptoms^13-21.

Through research from different studies, it was possible to verify some similarities in the interventions used by the various authors, who used parameters such as modality, intensity, frequency, volume and duration of the different types of exercises.

Given the diversity of exercises presented by the authors, they were grouped according to the associated intensity. We were able to verify that the study by Minghetti et al.¹³, comparing two groups of people, in which one of them practiced interval sprint training (high intensity exercise) and the other continuous aerobic physical exercise (moderate intensity exercise), found benefits of both physical exercise practices in the treatment of depressive disorders. Thus, it was not clear whether high-intensity physical exercise had a better conditioning when it is compared to moderate-intensity exercise.

This same line of thought was found by Helgadóttir et al.²¹ who, when comparing the different types of intensities of physical exercise practice, did not find significant differences between them. However, it was found that in the low intensity exercise group (yoga) there was a reduction of almost 2 points in the MADRS score compared to the moderate/aerobic exercise group.

Olson et al. ¹⁶, go against what has already been described, since these authors also concluded that the practice of light intensity exercise allows for improvements in the cognitive level and in the reduction of depressive symptoms.

Shuch et al.² report in their study that exercises of moderate to high intensity showed better results; however they highlight the fact that the study sample is small, being difficult to extrapolate.

But given the above, none of the articles managed to present advantages regarding the duration of the exercises. The exercise intensities ranged between light and moderate, with a variation in duration between 20-60 minutes^(16-18.20), with the exception of the high-intensity exercises¹³ which was performed in sessions of 25 repetitions of lasting 30 seconds (followed by 30 seconds of total rest).

Regarding the frequency of exercises, it ranged from one to three times a week for a period ranging from four to sixteen weeks^13-21.

It was found that the physical exercise performed more frequently^16,18,21 allowed to obtain more evident improvements than for those ones who only performed it once or twice^17,19.

When talking about the impact of physical exercise on people with depressive disorder undergoing pharmacological therapy compared to people with depressive disorder who underwent therapy at the behavioral level²¹, it was found that according to the MADRS score reductions in the three exercise groups were similar, and in all three were greater than the reduction observed in drug therapy. In the same perspective, Carneiro et al.¹⁸ found that the group of people undergoing pharmacological therapy combined with physical exercise had an improvement in quality of life and a reduction in depressive and anxiety symptoms, also improving physical fitness.

Pentecost et al.¹⁹ report that the use of self-help manuals in behavioral activation therapy with encouragement to exercise facilitated adherence to its treatment and proved to be an option to consider in the treatment of depressive symptoms.

In turn, Ólafsdóttir et al.²⁰ concluded that physical exercise can be a highly recommended alternative to the detriment of the transdiagnostic cognitive behavioral group. Minghetti et al.¹³, on the other hand, found that the association of these brought significant improvements in the reduction of symptoms of depression. Therefore, combining a physical exercise program with antidepressant therapy and cognitive behavioral therapy¹⁵ resulted in an improvement in cardiovascular capacity and a reduction in metabolic risk factors.

In the same line of thought, Helgadóttir et al.²¹ also found that physical exercise helped to prevent somatic disorders, such as cardio and cerebrovascular diseases and metabolic diseases. Knapen et al.¹ suggest that there is an improvement in the metabolic level. In addition to improving physical health, there was an improvement in terms of body image, coping strategies to deal with stress, consequently improving quality of life and independence in activities of daily living in elderly people with depression.

As the loss of muscle mass is a consequence of the depressive disorder, Kerling et al.¹⁴ concluded that the practice of regular aerobic exercise (resistance training) is effective in preserving mass in people with depression. However, the authors mentioned that more studies are needed to prove a concrete improvement in this field.

Knapen et al.¹ also reveal that the implementation of motivational strategies in exercise plans seems to improve the motivation of people with depression, as well as their long-term adherence to exercise.

Shuch et al.² also state that the results in the improvement of symptoms of depression using physical exercise are more evident when there are no other associated comorbidities and when the exercises were supervised by qualified professionals.

In other studies, it was possible to see evidence of physical exercise in reducing depressive symptoms. Tu et al.³ concluded that in people with stable heart failure and depression, physical exercise (aerobic and strength exercises) was beneficial in improving depressive symptoms and still has positive effects on self-esteem and social interaction.

Kerling et al.⁶ reveal that physical exercise has a positive impact on the serum concentrations of the neurotransmitter in the brain. An assessment of neurotransmitter levels before and after structured and supervised training in people with major depression has shown beneficial results and therefore exercise should be considered as an adjuvant treatment.

All these studies highlight the importance of physical exercise programs to be supervised by professionals with relevant training as it seems that the dropout rates of interventions decrease when given by these professionals (physical education teacher, health professionals, and instructors).

CONCLUSION

After the SLR, we can conclude that there is an improvement in quality of life, cognitive improvement, and decrease in depressive symptoms when practicing a training plan of exercises of light to moderate intensity under the supervision of health professionals in the treatment of depressive disorder.

The included studies recommend that the person with depression and under pharmacological therapy should remain physically active regardless of the type, frequency or intensity of physical exercise performed. In addition, the motivation, as well as the preference of physical activity to be practiced by the person with depression should be taken into account in detriment of a structured and rigid plan, thus obtaining better results.

Finally, the goal of depression treatment should not be limited to the remission of depressive symptoms, but focus on functional recovery, social participation and improvement of the person's physical health.

Considering the results obtained from this SLR, as well as its limitations, it seems essential to continue with the investigation in this field of knowledge, since physical exercise is a promising strategy and should be included as a treatment option for people with depression. And finally, objectively define the interventions and select the assessment instruments that allow measuring the level of effectiveness and also verifying the transferability of these interventions in other contexts.