* Aerobic and resistance training can reduce depressive symptoms in patients with major depressive disorder.

Depression causes the United States as much as $83 billion annually, in part because many people who have it don't seek treatment or don't receive benefit from treatment. The authors of a recent study analyzed the results of randomized controlled trials examining the use of exercise, either alone or in addition to medication, in the treatment of major depressive disorder.

Several studies involving adults (in varying age ranges) found that groups following aerobic exercise programs for eight to 16 weeks lowered depression scores, as compared with control groups. Similarly, resistance training programs undertaken for eight to 10 weeks significantly decreased depressive symptoms.

When exercise was compared with established treatments, such as selective serotonin reuptake inhibitors and psychotherapy, the result was comparable. When used in combination with other therapies, exercise produced higher response and remission rates, with higher-intensity aerobic exercise showing greater efficacy than lower-intensity exercise.

Based on the results, the authors developed the following conclusions and recommendations:

* Studies support the use of aerobic exercise; research on the effects of resistance training is less extensive.

* Ideally, patients should exercise three times or more per week.

* Aerobic training should focus on achieving 50% to 85% of a patient's maximum heart rate. Resistance training should incorporate upper- and lower-body exercises to achieve three sets of eight repetitions at 80% of the maximum weight that the subject can lift once.

* Exercise programs should be carried out for 10 to 12 weeks, although benefit has been shown at four weeks.

Exercise adherence should be promoted and supported.

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