Purpose: The purpose of this study was to examine the scientific evidence for a dose-response relation of physical activity with depressive and anxiety disorders.
Methods: Computer database searches of MEDLINE, PsychLit, and Internet and personal retrieval systems to locate population studies, randomized controlled trials (RCTs), observational studies, and consensus panel judgments were conducted.
Results: Observational studies demonstrate that greater amounts of occupational and leisure time physical activity are generally associated with reduced symptoms of depression. Quasi-experimental studies show that light-, moderate-, and vigorous-intensity exercise can reduce symptoms of depression. However, no RCTs have varied frequency or duration of exercise and controlled for total energy expenditure in studies of depression or anxiety. Quasi-experimental and RCTs demonstrate that both resistance training and aerobic exercise can reduce symptoms of depression. Finally, the relation of exercise dose to changes in cardiorespiratory fitness is equivocal with some studies showing that fitness is associated with reduction of symptoms and others that have demonstrated reduction in symptoms without increases in fitness.
Conclusion: All evidence for dose-response effects of physical activity and exercise come from B and C levels of evidence. There is little evidence for dose-response effects, though this is largely because of a lack of studies rather than a lack of evidence. A dose-response relation does, however, remain plausible.