Change in self-esteem, self-efficacy and the mood dimensions of depression as potential mediators of the physical activity and depression relationship: Exploring the temporal relation of change,☆☆

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Abstract

Objectives

Physical activity has been found to alleviate depression, but little is known about the mechanisms of change. This study assessed whether depression and hypothesised mechanisms – self-esteem, physical self-perceptions, self-efficacy, positive affect (PA) and negative affect (NA) – changed over time among depressed individuals who increased their physical activity. It also assessed the temporal relation of change.

Design

Longitudinal, within-subjects design.

Method

Thirty-nine individuals with elevated symptoms of depression increased their physical activity for an eight-week period. Measures of depression and the hypothesised mechanisms were taken at baseline, week one, week three and week eight.

Results

There were statistically significant improvements in depression and all the potential mechanisms between baseline and week eight. An initial reduction in depression was observed at week one, with most of the reduction occurring by week three. Initial improvement in PA, NA and self-efficacy also occurred at week one, while initial improvement in self-esteem and self-perceptions occurred at week three. Further improvement in self-esteem and some of the self-perception variables was observed after there was no further significant change in depression. There were larger changes in PA than the other measured mechanisms at weeks one and three.

Conclusions

Change in PA, NA and self-efficacy present stronger candidate mechanisms than change in self-esteem and self-perceptions for mediating change in depression, at least in the early stages of increased activity. An increase in PA may be especially important. However, a causal role for the potential mechanisms cannot be determined from this study.

Introduction

At any one time in the United Kingdom (UK), around 5% of the population will have a depressive disorder (Ohayon, Priest, Guilleminault, & Caulet, 1999). People with depression experience persistent low mood, a significant loss of pleasurable engagement in life and feelings of worthlessness, as well as many other cognitive and somatic symptoms (American Psychiatric Association, 1994). Evidence suggests that engaging in physical activity can help alleviate depression (Craft & Landers, 1998). At present, methodological limitations make it difficult to determine the clinical effectiveness and efficacy of physical activity. Lower effect sizes have been observed when studies have used more robust methods (e.g. intention-to-treat analyses) (Mead et al., 2008) or longer-term follow-up (Lawlor & Hopker, 2001). More studies using better quality research methods are needed (Lawlor and Hopker, 2001, Mead et al., 2008). However, at least among motivated volunteers, evidence suggests that physical activity may reduce depressive symptoms in the short-term and may be more beneficial than no treatment at all (Lawlor and Hopker, 2001, Mead et al., 2008).

While there is evidence that physical activity may reduce depression, very little is known about the mechanisms of change (Stathopoulou, Powers, Berry, Smits, & Otto, 2006). As with other interventions, it is important to understand the factors responsible for response, as more effective interventions may be designed (Kazdin & Nock, 2003). Based on psychological theory, suggested mechanisms have included improvement in self-efficacy (Bodin and Martinsen, 2004, Craft, 2005) and self-esteem (Van de Vliet et al., 2002). However, there has only been limited empirical research into hypothesised mechanisms (e.g. Bodin and Martinsen, 2004, Craft, 2005, Chu et al., in press, Foley et al., 2008) and the same potential mediators tend to be speculatively repeated in the literature. With the exceptions of Stathopoulou et al., 2006, Faulkner and Carless, 2006 and Foley et al. (2008), there have been few attempts to consider other theoretical frameworks that may help identify further hypothesised mechanisms. Stathopoulou et al. (2006) and Foley et al. (2008) consider the role of cognitive processes, including improved episodic memory through reductions in cortisol (Foley et al., 2008). Stathopoulou et al. (2006) further suggest that physical activity may work through behavioural activation processes. Faulkner and Carless (2006) draw on both the psychobiological theory of personality and the self-determination theory, to suggest that an increased sense of relatedness, autonomy and competence from physical activity may mediate reductions in depression.

Drawing on the tripartite model of anxiety and depression (Clark & Watson, 1991), we also propose a novel explanation. Physical activity may partly help depression through the impact that it has on the independent mood dimensions of depression (positive affect [PA] and negative affect [NA]). Physical activity may particularly tackle the low PA, anhedonia-related symptom of depression. To our knowledge, this explanation has not been previously proposed.

A commonality between some of the theories suggested is the potential role of feelings of competence, self-esteem and pleasant activation and engagement in explaining the physical activity–depression link. We suggest that the role of change in self-esteem, self-efficacy, NA and PA warrant further investigation. We now consider the theoretical rationales and evidence for these factors as potential mediators.

Section snippets

Mood dimensions of depression

Mood may be characterised by two independent dimensions known as PA and NA (Watson & Tellegen, 1985). High PA is a pleasurable state of energy, activation and engagement, whereas low PA reflects a lethargic and sad state. High NA represents feelings of distress and tension, whereas low NA is a peaceful and calm state. According to the tripartite model of depression and anxiety (Clark & Watson, 1991), depression and anxiety share a common high distress factor (high NA), but the anhedonia-related

Self-esteem

Depressed individuals often have a poor self-concept and experience feelings of low self-esteem (Fox, 2000). There is some evidence that physical activity may result in improvement in self-esteem and self-concept among people experiencing depression (Blumenthal et al., 1999, Ossip-Klein et al., 1989) and might therefore mediate changes in depression.

The exercise and self-esteem model (EXSEM; Sonstroem, Harlow, & Josephs, 1994) was developed from contemporary theory of self-concept which

Self-efficacy

Not only may change in self-efficacy potentially indirectly mediate change in depression through change in self-esteem from physical activity, but it may also be a direct mediator in its own right. Bandura (1997) suggests that all behavioural treatments may work by increasing self-efficacy. Self-efficacy is a person's level of confidence in their ability to perform particular behaviours to produce desired outcomes. Depressed individuals often have low levels of self-efficacy and Bandura (1997)

The present study

Crucial to establishing a factor as a mediator of change is the demonstration of temporal precedence. To infer causality, change in the potential mechanism(s) should be shown to temporally precede change in the outcome (Kazdin & Nock, 2003). While there has been some recent progress in examining the potential mediators of the physical activity–depression link within longitudinal or experimental designs (Bodin and Martinsen, 2004, Chu et al., in press, Craft, 2005, Foley et al., 2008), with the

Participants

With approval for the study from the university's School of Psychology Ethics Committee, participants (n = 47) were recruited via advertisements about the study at a university over a six-month period. Advertisements stated that we were seeking individuals who were currently experiencing low mood or depression to take part in a study of the psychological effects of physical activity and that participants would be reimbursed up to £50 for any physical activity costs incurred due to taking part

Attrition

Of the 39 participants who entered the study, nine dropped out of the study before the end of week 1, a further four dropped out by the end of week 3, and two did not return questionnaires for week 8. The complete dataset consisted of 24 participants who had returned questionnaires at each stage. This represented a 61.5% participant retention rate.

Differences between completers and non-completers

Analyses of baseline and demographic data were conducted to examine whether there were any differences at study entry between those who completed the

Discussion

The participants increased their level of physical activity in their own time over the eight-week period. Consistent with previous findings (Lawlor & Hopker, 2001), a reduction in depression was observed between baseline and the end of the increased physical-activity period for the completers and also in the intention-to-treat analysis. In terms of change in the potential mechanisms, over this period the participants also experienced improvements in PA, NA, self-esteem, physical

Conclusion

Individuals with elevated symptoms of depression may experience improvements in depression, self-esteem, physical self-perceptions, physical self-efficacy and state mood when they increase their physical activity. Improvements in depression, PA, NA and self-efficacy appear to be more immediate than change in self-esteem or physical self-perceptions. The findings suggest that self-efficacy, PA and NA may be stronger candidate mediators than self-esteem or physical self-perceptions, at least in

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    This research was supported by funding from The National Institute for Health Research National Coordinating Centre for Research Capacity Development.

    ☆☆

    This research was conducted as part of Karen White's PhD in Psychology at the University of Southampton.

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