Physical activity in depressed patients: a self-determination approach

Abstract

The aim of this Thesis was threefold: (i) to contribute to the clarification of the issue of causality between physical exercise and depressionamelioration in adult patients with major depressive disorder (18-65years), (ii) to investigate if self-determination theory (SDT) could revealpredictive properties towards depression relief and physical activity participation in adult outpatients (18-65years) with major depressive disorder, and (iii) to examine whether objectively measured habitual physical activity is associated with predictive effects on the improvement of depression in adult outpatients (18-65years) with major depressive disorder. The first study wasa critical review provided extensive interpretation of the literature referred to exercise for adult patients with major depressive disorder. Based on this study, physical exercise was associated with an improvement in depression, butdepressed patients participating in exercise on prescription schemes documented the highest dropout rates among all patients. Relevant recommendations based on SDT were provided in order to increase treatment effectiveness and to decrease dropout rates. In light of the inconclusive views seen in literature concerning the causal antidepressant effects of exercise, a systematic review was conducted to examineif exercise brings about clinically signficant antidepressant effects on adult patients with major depressive disorder. Based on normative comparisons, exercise led to an improvement in depression that was equivalent to general population. The most effective dose-response relationship was moderate intensity exercise ofthree times per week for both short- or longer-term (3, 8, or 9 weeks). A subsequent systematic review employed practical significance comparisons (meta-analytic techniques) toexploreif the aerobic modality of exercise in particular, compares favourably to routine practice treatment conditions. This meta-analysisfavoured the antidepressant effects of aerobic exerciseattributable to the large and significant overall effect-size and thelow heterogeneity levels. Also, no publication bias was recorded. Coding on participant, intervention, comparison, outcome and design characteristics did not change the result. The most-effective dose-response relationship referred to aerobic exercise of three times per week at moderate intensity for a short- (up to six weeks) or longer period (eight to twelve weeks). Following the supportive evidence for the causal antidepressant effects of exercise, the fourth study of this Thesis investigated the predictive contribution of SDT to depression relief and to physical activity participationin order to provide a robust rationale that could tackle the sedentary lifestyle of depressed patients and the disappointing dropout rates from exercise on prescription schemes. Based on a sample of 206 patients, this study revealed that need satisfaction (competence, autonomy and relatedness) is capable of predicting depression relief and physical activity participationincluding the corresponding metabolic equivalents by its own right as it overcome and neutralised the positive mediating effects of autonomous- (internal/identified)behavioural regulators(e.g., exercise for pleasure or for personal importance). Depression, however, illustrated an adverse toxic effect on need satisfaction. Controlling forms-(external/introjected)of behavioural regulators(e.g., exercise for external rewards or self-blame) typically comprising the iatrogenic physical activity/exerciseon prescription or promotion model showed no mediating effect.Finally, given that the selfadministrative health behavioural pattern of habitual physical activity may represent the frontline treatment tool against depression, the fifth study of this Thesisrecruited 19 depressed patients to explore whether objective habitual physical activity levels measured by means of a 7-day use of triaxial accelerometer devices are associated withantidepressant predictive properties. The study recordedan average of 32 minutes of moderate to vigorous habitual physical activity per day. This amount of habitual physical activitypredicted depression ameliorationand explained 23% of the variance of depression. It should be noted that only 40 seconds of the 32 minutes represented the vigorous component.Collectively, this Thesis has found that physical exercise shows causal antidepressant effects. Also, satisfying the SDT dendrites of psychological needs for exercise may lead to depression relief as well as to participation in physical activity. Finally, the objectively measured level of moderate to vigorous habitual physical activity for 32 minutes per day is related with depression amelioration.Studies 4 and 5 need to be replicated with a longitutinal design in order to draw causal conclusions.Also, the implementation of pragmatic randomized controlled trials is essential in order to translate into real life settings the clinical evidence referred to the antidepresiveness of physical activity/exercise and the predictive power of SDT towards physical activity participation.