Depression is a common mental disorder that presents with depressed mood, loss of interest or pleasure, feelings of guilt or low self-worth, disturbed sleep and/or appetite, low energy, and poor concentration. Depression is a widespread and often chronic condition. Lifetime prevalence estimates for major depressive disorder are approximately 15% to 20%; 1-year prevalence estimates are 5% to 10%. Moreover, depression is characterized by high rates of relapse: 22% to 50% of patients suffer recurrent episodes within 6 months after recovery.
Depression is associated with a high incidence of co-morbid somatic illness. Individuals suffering from major depression run a higher relative risk of coronary heart disease, type 2 diabetes and osteoporosis compared with the general population. In general, depressed individuals exhibit a less active life-style and have a reduced cardio-respiratory fitness in comparison with the general population. Strong evidence demonstrates that lack of physical activity is associated with an unhealthier body mass and composition, and a biomarker risk profile for cardiovascular disease, type 2 diabetes, and osteoporosis. A growing body of evidence suggests that exercise is an effective treatment for depression. For mild to moderate depression the effect of exercise may be comparable to antidepressant medication and psychotherapy; for severe depression exercise seems to be a valuable complementary therapy to the traditional treatments. Exercise training not only improves depression, but also produces ‘positive side effects’ on depression associated physical diseases and cognitive decline.