Depression is a serious mental disorder in the U.S. Each year, approximately 13.7 million American adults suffer from depression. Research has shown that exercise can decrease depressive symptoms, yet an optimal exercise program for treating depression has not been established. The mechanisms that mediate the antidepressant effect of exercise also require investigation. The purpose of this study was to examine the effect of different exercise intensities prescribed for aerobic training on depressive symptoms in initially sedentary depressed women. A secondary purpose was to examine the mediation effect of self-efficacy on depression.
Sedentary women scoring ≥ 14 on the Beck Depression Inventory-II (BDI-II) were randomized to one of two aerobic exercise treatment groups that differed on exercise intensity [high (65-75% MaxVO2 reserve) or low (40-55% MaxVO2 reserve)], or to a stretching exercise control group. All three groups had one supervised exercise session per week. The aerobic groups also exercised 3-4 times per week on their own and exercised to expend 1000 Kcal per week. The total training period was 10 weeks. Participants' depressive symptoms (BDI-II) and self-efficacy (Exercise Self-Efficacy Questionnaire and Depression Coping Self-Efficacy Scale) were measured at study entry, week 5, and week 10.
Results showed that participants in all groups (high, n = 15; low, n = 11; stretching, n = 12) had significant reductions in depressive symptoms after 10 weeks, p < .001. The BDI-II change scores were not significantly different among the groups. After 10-weeks of exercise training, participants in both aerobic exercise groups had significantly increased depression coping self-efficacy, p < .01, but their exercise self-efficacy did not change. Neither exercise self-efficacy nor depression coping self-efficacy had significant correlation with BDI-II changes. There was no mediation effect for either type of self-efficacy.
It was concluded that when controlling total energy expenditure (1000 Kcal per week), both high and low intensity aerobic exercise training programs were equally effective in reducing mild to moderate depressive symptoms in initially sedentary women. While depression coping self-efficacy improved for the two aerobic groups, there was no evidence that self-efficacy mediated the effect of exercise training on depressive symptoms.