**5. Physical activity and exercise for mental benefits**

Several meta-analytic studies have investigated the association and the impact of physical activity on mental health outcomes. The results vary in efficacy degrees depending on methodological considerations, including study quality and duration [34].

Meta-analyses of prospective cohort studies have found that physical activity had a protective effect against the emergence of depression [35]. Also, physical activity protects against anxiety symptoms [36]. The association seems to be proportional since a higher level of physical fitness was associated with a lower onset of mental health problems [35]. In addition, sedentary behaviour is associated with an increased risk of depression [37] and anxiety [38].

Exercise exerts a causal influence on mental health disorders since exercise has a significant antidepressant effect in people with depression (including major depressive disorder) [39] and could improve anxiety symptoms in people with a current diagnosis of anxiety or stress-related disorders [40]. The antidepressant effect of aerobic exercise interventions was examined in a meta-analysis study and showed a significantly large effect [41]. The analysis revealed comparable effects across various settings and delivery formats, regardless of symptom severity in both outpatients and inpatients.

Furthermore, we can look forward and analyse the association between cardiorespiratory fitness (CRF) and common mental disorders. CRF captures broad physical activity trends with one discrete test using objective, clearly defined markers, such as oxygen consumption. The studies found that low and medium CRF is associated with an increased risk of common mental health disorders, namely depression [42] and anxiety [43].

Beyond cardiorespiratory fitness, muscle strength has also been associated with mental disorders. Increased hand grip strength may be associated with lower odds of developing generalised anxiety disorder [44]. Hand grip strength has been considered an important predictor of depressive symptoms in middle-aged and older adults [45].

Although several studies have demonstrated that physical activity can be used to prevent and treat common mental health disorders, most of the evidence assessed physical activity in general without analysing a dose-response of exercise, neither intensity, type, or other important aspects of exercise prescription.

### **5.1 Dose-response of the association between exercise and mental health functioning**

Incremental increases in cardiorespiratory fitness are associated with proportional decreases in the risk of new-onset common mental health disorders, indicating a dose-response relationship between exercise and mental health disorders [43]. A national population-based study reveals that a minimal level of at least 20 min per week of physical activity guarantees mental health benefits. However, dose-response patterns demonstrated greater risk reduction for activity at a higher volume and intensity [46].

Meta-analyses of prospective cohort studies reveal that completing 150 min/week of moderate-vigorous physical activity reduces the risk of developing depression by about 22% [35]. However, low levels of physical activity (e.g., walking <150 min/ week) can prevent future depression [47].

Exercise duration significantly moderates the effect of endurance intervention on depressive symptoms, and an extended exercise duration strengthens the antidepressant effect of endurance exercise interventions [48].

Regarding the bouts of exercise, a systematic review showed that short bouts (10–15 min) of physical activity had a significant effect on reducing stress and depressive symptoms and improving self-esteem among adults without mental health conditions [49].

Considering multiple dose-response curves of exercise regarding different health outcomes [50], no consensus about the optimal dose of physical activity to prevent or treat mental health was founded. For an increment of physical activity for the general population with mental health conditions, the World Health Organization policy seems to be a good way when proclaiming that "any movement counts" [33]. However, considering exercise prescriptions for each mental health condition, more systematic reviews of randomised controlled trials are needed to clarify the optimal dose response.

#### **5.2 Intensity**

A meta-analytical review concluded that increased exercise intensity of neuromuscular exercise strengthened the antidepressant effect among depressed adults [48]. Among older people with depression, moderate-intensity physical activity significantly affected depression [39]. Cross-sectional and prospective studies have demonstrated that moderate and vigorous physical activity intensity is associated with lower odds of depressive symptoms [51]. The best intensity to deal with depressive symptoms still needs more investigation.

A scoping review showed that there is not always a direct association between mental health and exercise duration/intensity [52]. In a study carried out with retired older adults, it was found that high-intensity physical activities had a negative impact on the perception of well-being [53]. A systematic review with meta-analysis of randomised controlled trials on sleep quality and insomnia in middle-aged women concluded that moderate levels of programmed exercise (aerobic exercise) indicated a positive effect on sleep quality. In contrast, low-intensity exercises did not reveal a significant effect [54]. These findings suggest that high-intensity exercise may not be the best strategy for well-being in the middle-aged and older adult population. A possible explanation is that this population tends to exercise to maintain physical fitness and also seek prosocial benefits, such as minimising isolation [55]. Consequently, practising exercises associated with social contact reflects positively on mental health [56]. Thus, moderate intensity seems to be the most useful measure of mental well-being.

#### **5.3 Type of exercise**

A meta-analysis including 1877 participants found that resistance exercise training was associated with a significant reduction in depressive symptoms, with a moderatesized mean effect. However, a smaller reduction was observed when considering only trials with blinded allocation and assessment [57]. Similar anxiety results were found in another meta-analysis involving 922 participants, where resistance exercise training improves anxiety symptoms among healthy participants and participants with physical or mental disorders [58]. Combined aerobic moderate-vigorous physical activity and muscle-strengthening exercise were associated with the lowest likelihood of reporting depressive symptoms, analysed in a large population-based sample of adults (17,839 participants) [59].

Thus, when comparing aerobic exercise only and muscle-strengthening exercise only, no difference between modalities in reducing depressive symptoms was founded [42].

*Mental Health Conditions and Exercise DOI: http://dx.doi.org/10.5772/intechopen.111505*

But adults who practice aerobic and muscle-strengthening physical activity combined had the lowest likelihood of depressive symptoms compared to those who adhere only to one exercise modality [59].

Other meta-analytical reviews revealed a moderate to large effect in favour of endurance exercise and a large effect in favour of neuromuscular exercise, compared to control conditions, to reduce depressive symptoms among depressed adults [48].

Among older adults with depression, a meta-analysis of randomised controlled trials found that mixed aerobic and anaerobic interventions significantly affected depression compared with the control group [39].

### **6. Conclusions**

Mental health conditions represent a major impact on public health globally. People with mental conditions may be affected by several determinants related to physical, emotional, and social domains. This chapter aimed to elucidate alternatives to deal with mental conditions, highlighting the importance of physical activity and exercise. This underscores the importance of a multi-disciplinary approach to improve mental health that incorporates exercise as an essential part of treatment and prevention strategies. We present several mechanisms (neurobiological and behavioural) that are involved in the association between exercise and mental conditions. In line with the most recent guidelines, we expose the World Health Organization's general physical activity recommendation. Despite several evidence demonstrating the association between exercise and improvement in mental health outcomes, there is still a lack of clear guidelines on how to prescribe exercise based on the specific mental health condition and the principles of exercise (frequency, intensity, type, and duration). To finish this chapter, we present several pieces of evidence demonstrating the impact of exercise on mental health outcomes and explore the difference in dose response, intensity, and type of exercise.

The positive effects of physical activity and exercise on mental health are particularly relevant for public health interventions aimed at preventing and treating mental health disorders. We expected that this chapter would help future studies to fill some gaps in the literature and help health professionals to have a better understanding of the relationship between exercise and mental health outcomes.
