An investigation into the effect of exercise on clinical depression.

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An investigation into the effect of exercise on clinical depression

Problems with depression are by no means limited to those who are clinically diagnosed as being so. Generalised, negative affect is experienced by everyone throughout the course of a lifetime. Usually, non clinical depression is linked to some kind of stressor in the environment which can be clearly identified, for example, the termination of a job. It is only when these depressive episodes go further than certain boundaries of intensity, duration and frequency can the disorder can be labelled clinical depression. Depressive symptoms, e.g. sadness, disturbed sleep and fatigue can also be symptoms of other medical conditions (for example stroke) however, in this situation depression may not require a separate diagnosis. Clinical depression is a very prevalent problem in today’s society; 15% of people will have an episode of major depression in their lives and it is said to be the fourth most common cause of disability worldwide (NHS Website 2004). One of the earliest treatments for depression was psychotherapy, but Dishman (1986) notes than in severe cases medication will almost certainly be required. In the past 10 years or so, ‘exercise on prescription’ schemes have become popular in primary health care, many of which include depression in the referral criteria. (Biddle and Fox 1991) Strict diagnostic criteria are crucial since one of the problems with studies considering the effect of exercise and depression is a lack of agreement between researchers as to the criteria. Many reviews in the area include cases where depression could not be defined as clinical but more as negative affect. The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) contains a list of criteria for diagnosing depression (See appendix 1). A major depressive episode is categorized by either a depressed mood or loss of pleasure in all or most activities, and the presence of other symptoms for at lease 2 weeks. The gold standard for diagnosing depression and distinguishing it from negative affects is an interview that is performed by a clinician. The most common questionnaire is the Beck Depression Inventory (BDI) (Beck, Ward, Mendelson, Mock, & Erbaugh, 1961).

The Profile of Mood States (POMS) is a measure created by McNair in 1971 with the intent of measuring mood states; it is a widely used measure that has been used on psychiatric patients as well as in sport and exercise settings (Berger and Motl 2000). However, for the purpose of this investigation only studies where the participants are diagnosed as having clinical depression, rather than just scoring low in the POMS will be considered.

Traditional treatments for depression can be highly costly and ineffective, for example, psychotherapy and pharmacology (Byrne & Byrne, 1993). Similarly, drug treatments can cause unpleasant side effects such as dependence, fatigue and cardiovascular problems (Martinsen, 1990). This highlights the need for an alternative treatment and an ever growing amount of research suggests that exercise may be best suited to fill this roll. The relationship between exercise and depression has been examined since the early 1900’s when Franz and Hamilton (1905) recommended moderate to active exercise in alleviating the symptoms of depression. Since then there has been a vast amount of studies completed in this growing area. These were originally cross-sectional designs comparing the physical activity and physical capacity levels of depressed and non depressed individuals (Morgan, 1969; Morgan, 1970). Following these studies were interventions, looking at using exercise as a way of alleviating depression

Epidemiological Evidence

William Morgan was the initial researcher in the area of exercise and mental health, what initiated his research was his finding that hospitalised patients had lower exercise levels than non-hospitalised controls (Morgan, 1969; Morgan, 1970; Morgan, 1968). This work provided other researchers, including the pioneer, with an incentive for looking more closely at specific areas of mental health, including depression. Since the work of Morgan there have been a number of epidemiological studies completed in the area, with the strongest evidence coming from four prospective studies (Biddle and Mutrie 2002). Two of these four will be considered here.

        Farmer, Locke, Moscicki, Dannenberg, Larson and Radloff (1988) conduced a large survey with 1497 respondents. The researchers found that over an 8 year period women who completed little or no activity were twice as likely to have an onset of depression than the respondents who took part in ‘much’ or ‘moderate’ activity. During the study a number of other variables were accounted for such as age, employment-income, education and chronic medical conditions. (Biddle et al 2002).

        The second study was conducted by Camacho, Roberts, Lazarus, Kaplan, and Cohen, (1991) on a large population in California. Baseline data was collected in 1965 and the follow up data in 1974 and 1983. After the first follow up in 1974 the researchers found that the risk of showing depressive symptoms was significantly greater for men and women who were categorised as low active in the baseline measure. This relationship was found to be similar in the moderately active group when compared to the high active one. During the second follow up (1983) four categories for activity levels were fashioned:

  1. (Low/Low) Participants who were low active in 1965 and also in 1974.
  2. (Low/High) Participants who were low active in 1965 and then increased activity level in 1974.
  3. (High/Low) Participants who had been high active in 1965 but decreased in 1974.
  4. (High/High) Participants who had been highly active in 1965 and 1974.
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 These classifications and results are shown in figure 1. below.

Figure 1: Changes in physical activity status and subsequent depression

(Camacho et al . 1991. Table adapted from Biddle et al 2002)

As shown in the table above, those who increased their physical activity levels from 1965 to 1974 were no more likely to develop depression than those who had been active at both times. The odds ratio was computed and showed that those who decreased their activity levels from 1966 to 1974 were 1.6 times more likely to develop depression than those who maintained a high level. Although ...

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