with which the physical activity is conducted. In this regard, Mutrie (2001) reported that
moderate levels of such activity (e.g., taking a brisk walk) tend to produce more positive
effects on people’s sense of well-being than do more vigorous activities such as jogging
or running.
A second finding in this field is that frequent exercise is associated with a reduction in
reported symptoms of depression (e.g., Martinsen and Morgan, 1997). To evaluate this
relationship more rigorously, Lawlor and Hopker (2001) conducted a meta-analysis of
studies in this field. Adopting strict inclusion criteria, these authors focused solely on
studies which had used randomised controlled trials in their research design. By
combining relevant results from fourteen such studies, these authors discovered that
physical activity had a relatively large effect on depression scores when compared with
data yielded by control conditions. Interestingly, the results also showed that the effects
of such activity on depression were similar to those of cognitive therapy—a finding
which raises the intriguing possibility that exercise can be prescribed as a form of therapy
for people who are depressed (see also Sime, 2002). Incidentally, among the putative
mechanisms for this effect is the neurobiological possibility that exercise triggers the
release of “morphine-like”, pain-reducing neurotransmitters in the brain. Alternatively,
exercise may give people a “time out” from their daily stresses and/or boost their self-
esteem. Box 8.2 explores these rival explanations of the psychological effects of exercise
behaviour.
Box 8.2 Explaining the beneficial effects of physical activity: is it all in
the mind?It is widely agreed that people who are physically active tend to report significantly lower
rates of anxiety and depression than do their more sedentary counterparts. What
theoretical mechanisms could account for this finding?
Exercise psychologists have proposed at least three possible explanations for this
relationship. These three explanations—the neurobiological, cognitive and “self-efficacy”
theories—may be summarised as follows. First, advocates of the neurobiological
approach argue that both acute and chronic physical activity triggers the release of
neurotransmitters such as norepinephrine or serotonin in the brain (e.g., Hoffmann, 1997;
Chauloff, 1997), This release is alleged to reduce the painful effects of exercise while
enhancing concomitant pleasurable sensations. Unfortunately, although the “endorphin
hypothesis” has great popular appeal, it is poorly supported scientifically. Thus few
studies have reported any evidence of empirical associations between exercisers’ mood
changes and their release of endorphins (Buckworth and Dishman, 2002). Next,
proponents of cognitive explanations of exercise effects (e.g., Morgan, 1985) tend to
emphasise a “distraction” or “time out” effect Briefly, the idea here is that exercise offers
participants a period of respite from the stresses and worries of everyday life. One
implication of this theory is that it is not the exercise itself but the change in context in
which it occurs that enhances people’s sense of psychological well-being. Unfortunately,
as the evidence bearing upon this theory is somewhat equivocal (e.g., see Bodin and
Hartig, 2003), its explanatory value is questionable. The third explanation of beneficial
exercise effects comes from research on “selfefficacy” or people’sbeliefs in their
Sport and exercise psychology: A critical introduction 222