Positive affect mediates the effect of a telephone-based exercise intervention on depression in a sample of individuals with multiple sclerosis.
|Title||Positive affect mediates the effect of a telephone-based exercise intervention on depression in a sample of individuals with multiple sclerosis.|
|Publication Type||Journal Article|
|Authors||Kratz A, Bombardier CH, Ehde DM|
|Journal||International Journal of MS Care|
Background: Evidence from survey and intervention studies has shown that exercise is associated with reduced depressive symptoms and rates of depressive disorders in the general population and among those with multiple sclerosis (MS). We have previously found that a telephone-based exercise intervention resulted in significant reductions in depressive symptoms in an MS sample. However, we have yet to identify mechanisms by which the intervention is related to positive changes in mood. Objectives: The aim of this study was to test negative affect (NA) and positive affect (PA) as mediators of the treatment effect on depressive symptoms. Methods: Participants were 99 adults (14 male; Mean age = 48.8 years) with MS and major depressive disorder who were randomized to treatment (48) or wait-list control group (51). Measures of exercise in the past week, NA and PA (PANAS, Watson, Clark, and Tellegen, 1988), and depressive symptoms (HAM-D, Hamilton, 1960) were administered at baseline and 12 weeks post-baseline. The intervention, based on the principles of Motivational Interviewing (Miller & Rollnick, 2002), included an initial 60-minute session followed by 11 weeks of 1X/week 15-30 minute phone sessions. Mediation was tested with a path-analysis model (using MPlus 5.21 statistical program), predicting change in depressive symptoms from treatment/control, with changes in physical activity, PA and NA as mediational variables. Results: Results indicated that the treatment was associated with increased physical activity (β=.26, P=.01) and PA (β=.25, P=.01), and decreased NA(β=-.35, P<.01) and depressive symptoms(β=-.20, P=.01). Furthermore, the effect of treatment on PA was mediated by increased physical activity; PA, in turn, mediated the association between increased physical activity and decreased depressive symptoms. Physical activity was not related to NA and NA did not mediate the treatment effect on depression. Conclusions: Findings from path analyses suggest that the effects of the exercise treatment on depressive symptoms are partially mediated by changes in positive affect, which are related to increases in physical activity.