Several studies have found exercise to be an effective treatment for depression (34,35,44). In a recent meta-analysis (30), the researchers concluded that exercise was superior to no treatment and was as effective as cognitive therapy in treating depression. To date, only one study has examined the use of exercise compared with antidepressant medication (sertraline hydrochloride) as a treatment for MDD in older adults. In this study (8), 156 middle-aged and older adults diagnosed with MDD were randomized to supervised exercise, sertraline, or a combination of exercise and sertraline. The 16 wk exercise treatment consisted of three weekly sessions of aerobic activity. By the end of the treatment period, each of the three treatment groups experienced a significant reduction in their levels of depression. The treatments did not differ significantly from one another in efficacy, suggesting that exercise may be a viable alternative to medication in the treatment of MDD.
A follow-up assessment completed 6 mo after treatment was initiated (3) showed that those individuals assigned to exercise alone experienced lower rates of depression than did those who received medication or a combination of exercise and medication. In addition, only 9% of remitted participants in the exercise group relapsed, compared with more than 30% of participants in the medication and combination groups. Another finding was that 64% of participants who received the exercise treatment continued to exercise following completion of the program. Self-reported exercise among all participants was associated with a 50% reduction in risk of depression 6 mo after the study ended. In sum, exercise may be as effective as antidepressant medication in the reduction of depressive symptoms.
A number of potential mechanisms may be responsible for the reduction in depressive symptoms associated with exercise (10). For example, the central monoamine theory suggests that exercise corrects dysregulation of the central monoamines believed to lead to depression. Psychological factors also may be responsible for exercise-related improvements in mood. One hypothesis is that exercise reduces depression through increases in self-esteem and self-efficacy. Other potential psychological mechanisms include the distraction from negative emotion provided by exercising as well as the behavioral activation occurring with exercise, which is also an important component of CBT for MDD. The issue of how much exercise is needed to achieve an anti-depressant effect is also an important topic, one that is discussed in practical application 9.3.
In general, studies have demonstrated the effectiveness of exercise in treating depression. One question that remains unanswered is the dose of exercise required to obtain an antidepressant effect. Specifically, what frequency, intensity, and duration are most beneficial in treating patients with depression? Dunn and colleagues (16) recently completed a trial that was designed to address this issue. In this trial, 80 sedentary adults diagnosed with major depressive disorder (MDD) were randomized to undergo 12 wk of one of five aerobic exercise-training treatment conditions: low energy expenditure and 3 d of exercise training per week, high energy expenditure and 3 d of exercise training per week, low energy expenditure and 5 d of exercise training per week, high energy expenditure and 5 d of exercise training per week, or stretching and flexibility control.
Results of the trial showed that exercise conducted at the high energy expenditure dose (consistent with public health recommendations) was effective in reducing depressive symptoms (47% from baseline measurement) over the 12 wk treatment period. In contrast, although participants randomized to the low energy expenditure dose did experience some reduction in depression over the treatment period (30% from baseline measurement), those participants did not respond significantly better than participants in the control condition did (29% from baseline measurement). Regarding frequency of training, no significant difference in treatment response was found between those participants who exercised 3 d per week relative to those who exercised 5 d per week. This result identifies total energy expenditure as the key aspect of exercise dose related to remission of MDD, regardless of days per week exercised.
In summary, this trial demonstrated that an exercise-training dose consistent with public health recommendations for energy expenditure is effective for the treatment of MDD in previously sedentary adults. Importantly, an exercise prescription that includes lower energy expenditure does not appear to be beneficial in reducing depressive symptoms. Thus, exercise professionals should encourage depressed patients to achieve at least the minimum recommended levels of energy expenditure.