When women feel sad and blue, they typically tend to brood and dwell on the fact that they are unhappy. But men cope very differently when their spirits are low with a tendency toward action and activity. The American Psychological Association (APA) says that is the reason why women are at higher risk for depression than men, and why one in four women will be diagnosed with severe depression in their lifetime. It is now well documented that exercise can help depression, and possibly even prevent it. An explanation of depression, discussion of scientific studies of depression and exercise, theories on why exercise can help depression, and recommendations for exercise will be highlighted in this article.

Defining Depression
Sometime in everyone’s life, feelings of sadness and melancholy may permeate their being. These feelings come and go and life goes on. Yet major depression is a mood disorder characterized by one or more major depressive episodes [1]. This means being in a depressed mood for at least two weeks and a loss of interest or pleasure in nearly all activities. At least four additional symptoms must accompany this such as changes in sleep, appetite, or weight; decreased energy; feelings of worthlessness or guilt; difficulty thinking, concentrating, or making decisions; or recurrent thoughts of death or suicidal ideas, plans, or attempts. The APA gives the warning signs of depression as: a depressive mood; feelings of helplessness and pessimism; sleep disturbances like the inability to sleep, sleeping too much, or having irregular sleep patterns; appetite disturbances like eating far less or far more than usual; social withdrawal; blaming yourself for your problems, or feeling that you're worthless; inability to concentrate, even on routine tasks; and substance abuse. The APA states that women in particular are vulnerable to depression because of reproductive issues, personality styles (women may be passive, dependent, pessimistic, or negative), sexual and physical abuse, and the multiple roles that marriage and having children bring. Physiologically in depression, certain neurotransmitters are decreased. Neurotransmitters are chemical messengers that communicate between nerves. In depression, the monoamine neurotransmitters norepinephrine and serotonin are decreased [2]. It is thought that the appropriate amounts of norepinephrine and serotonin increase a person’s happiness and contentment, maintain a person’s normal appetite and sex drive, and provide a psychomotor balance.

Depression and Exercise
The general consensus on people who are physically active is that they have an enhanced mood, higher self-esteem, greater confidence in their ability to perform tasks requiring physical activity (greater self-efficacy), and better cognitive functioning than people who are sedentary or less physically fit [3]. In general, people who are inactive are twice as likely to have depression symptoms than more active people. The latest research on treatment for depression shows that exercise is a viable, cost-effective treatment for depression and may even help in the treatment of other mental disorders [4]. The authors of this research reviewed 14 studies since 1981 in which exercise was used as an intervention in treating individuals with clinical depression. They found that nonaerobic forms of exercise, such as strength training, are as effective as aerobic exercise in treating depression. The researchers also found that less strenuous forms of regular exercise, such as walking, may be sufficient to demonstrate significant treatment effects. When considering the evidence that exercise is a viable, cost-effective treatment for depression, the researchers say that they are surprised that exercise has not become a more popular treatment alternative and suggest that it become more commonly used by clinicians as part of a treatment program.

Why Does Exercise Work?
The jury still seems to be out on exactly why and how exercise benefits depression. Many theories have been proposed, but more than likely, it is a combination of events that promote the positive effects. Some psychological theories on the positive effects exercise has on depression are that exercise leads to increased self-mastery or self-efficacy, it provides social interaction and support, it provides a form of meditation, it provides a form of distraction away from negative thoughts or behaviors, or that exercise is a pleasant activity and is positively reinforcing [3, 4]. Some physiological theories are the thermogenic theory, where it is supposed that the increased body temperature from exercise decreases muscle tension; the endorphin theory that states endogenous opiates in the body are released during exercise; and the monoamine neurotransmitter theory that conjectures increased levels of norepinephrine and serotonin are released during exercise. There is little evidence on the endorphin theory, and researchers are leaning toward a combination of psychological theories along with the neurotransmitter theory. Some researchers think that exercise may help the brain cope better with stress or that it gives the body a way to deal more appropriately with stress. Science is currently studying the link between exercise and the brain chemicals associated with stress, anxiety, and depression.

Exercise and Normal Mood
The effect of exercise on normal mood has yielded inconsistent findings, mostly because of testing difficulties and inconsistencies. Many studies have used the same testing methods and scales on healthy people that they use on clinically depressed people. The scales that are utilized to measure clinical depression may not allow for enough improvement for people who are feeling fine to begin with. Studies with these shortcomings taken into consideration have shown positive effects of exercise on normal psychological health. One study compared the effects of different intensities and formats during 12 months of exercise training on the psychological outcomes in older adults. The results showed that exercise, either inside or outside the home or of a high or low intensity, reduced stress and anxiety [5]. The conclusion was that neither a group format nor vigorous activity was essential in attaining psychological benefits from exercise training in healthy adults. Also, the psychological benefits were independent of changes in fitness or body weight. In a study on those who maintain the exercise habit, a brief period of exercise deprivation resulted in mood disturbance within 24-48 hours [6].

Do Something
The research on exercise and clinical depression shows that improvements can be made with five weeks of three times a week aerobic exercise or nonaerobic exercise of low to moderate intensity (50% of maximum heart rate) for 20-60 minutes [4]. Follow-up research has shown that gains can be maintained for up to one year, especially if some level of physical activity is continued [7, 8]. Of course, medical clearance should always be obtained before beginning any exercise program. Exercise should begin slowly in frequency, duration, and intensity. Exercise shouldn’t be thought of as an overwhelming task, but as a manageable part of a daily schedule. Options to formal exercise programs or structured classes can involve functional activities of daily living like performing squats when doing housework or walking to work. The key is to just do something, and to make it a habit. Healthcare providers may prescribe medications and nutritional supplements that can alleviate the symptoms of depression. Some organizations that can help for depression are: American Psychological Association at www.apa.org; National Alliance for the Mentally Ill (NAMI) at 800-950-6264; National Depressive and Manic Depressive Association at 800-82-NDMDA; National Mental Health Association (NMHA) National Mental Health Information Center at 800-969-6642; National Foundation for Depressive Illness, Inc. at 800-248-4344.

References
1. American Psychiatric Association. Diagnostic and statistical manual of mental disorders. Vol. 4th ed. 1994, Washington, DC.
2. Guyton, A.C. and J.E. Hall, Textbook of Medical Physiology. 9th ed. 1996, Philadelphia: W.B. Saunders Company. 573;767.
3. Physical activity and health: a report of the surgeon general. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, 1996: p. 135-142.
4. Tkachuk, G.A. and G.L. Martin, Exercise therapy for patients with psychiatric disorders: research and clinical implications. Professional Psychology: Research and Practice, 1999. 30(3): p. 275-282.
5. King, A.C., C.B. Taylor, and W.L. Haskell, Effects of differing intensities and formats of 12 months of exercise training on psychological outcomes in older adults [published erratum appears in Health Psychol 1993 Sep;12(5):405]. Health Psychol, 1993. 12(4): p. 292-300.
6. Mondin, G.W., et al., Psychological consequences of exercise deprivation in habitual exercisers. Med Sci Sports Exerc, 1996. 28(9): p. 1199-1203.
7. Ossip-Klein, F.J., et al., Effects of running or weight lifting on self-concept in clinically depressed women. Journal of Consulting and Clinical Psychology, 1989. 57(1): p. 158-161.
8. DiLorenzo, T.M., et al., Long-term effects of aerobic exercise on psychological outcomes. Prev Med, 1999. 28(1): p. 75-85.