It is well recognised in clinical and research settings that patients with depression account for a large portion of those seeking healthcare. In a large study of the 12-month and lifetime prevalence of mental disorders among the European population, major depression was found to be the single most common disorder with a lifetime prevalence of 12.8% and a 12-month equivalence of 3.9% . In the year 2020 it is expected that depression will be the world-wide second largest disease-related cause of disability, second only to heart disease . In addition to the personal suffering involved, depression is a major source of economic strain for society. The total annual cost of depression in Europe in 2004 has been estimated to €118 billion, corresponding to 1% of the total European economy at the time .
Treatments of depression include both pharmaceutical (antidepressants) and psychological (psychotherapy), with research showing near-equal efficacy between them . Unfortunately, research also indicates that far from all who suffer from depression seek treatment . A wider treatment arsenal including low-cost, high-flexibility treatments is therefore desirable. One promising treatment is activation, two kinds of which are behavioural activation, and one solely focused on physical exercise. These two kinds of activation therapy have the potential to be administered via the Internet, which would both lower the threshold for those seeking treatment, while also providing effective treatment to a low cost. In this therapeutic context, physical exercise can be considered a focused form of behavioural activation  in the respect that both interventions require the client to schedule and perform activities. A recent innovative randomised controlled trial comparing aerobic exercise to low-intensity stretching - both treatment arms having equal levels of activity frequency and social interaction - found no between-group difference in antidepressant effect . An explanation for this result could be that it was the common activation component that caused the antidepressant effect, rather than the physical exercise per se. At present it is unknown whether any antidepressant effects of behavioural activation and physical exercise are treatment-specific or due to the common activation factor. Using an advanced trial design, the study herein described will be able to evaluate the antidepressant effects of both the respective treatments in themselves, and compare the two.
Strategies now known as behavioural activation (BA), originally developed by Lewinsohn and colleges in the 1970s, focused on pleasant events scheduling and BA is now defined as a structured, brief psychotherapeutic method to: (1) increase engagements in adaptive (appetitive) activities; (2) decrease engagements in activities that maintain or increase depression; and (3) increase access to reward . A 2007 meta-analysis found BA to have a large effect on depressive symptoms, with the added benefit of being relatively uncomplicated, time-efficient and not requiring complex skills of patient or therapist . Explaining the BA treatment rationale to patients is widely considered an early step in treatment , yet the component-specific effect of providing this rational has not yet been the subject of research. Acknowledging the well-known effect on outcome in cognitive behavioural therapy of the client’s acceptance of treatment rationale , this study will be able to distinguish the effect of providing a clear and extensive treatment rationale in BA therapy. This study will also be the first to test whether BA therapy can be adequately administered via the Internet (see [6, 11]).
A 2007 Cochrane review found physical exercise to have a large clinical effect on depression. If however the methodologically weak studies were excluded, the clinical effect was moderate and non-significant . Acknowledging the methodological weaknesses of previous studies, a more recent meta-analysis including only randomised controlled trials suggests a large and significant effect of physical exercise on depression . It should be noted that the causality of physical exercise as treatment of depression has been questioned. In a large population-based study, De Moor et al.  found that in genetically identical twins, the twin who exercised more did not display fewer symptoms of depression, suggesting that the causal role should be ascribed to a common genetic factor rather than the exercise itself. Indeed, the specific mechanism by which physical exercise has an effect on depression, if any, is still unknown. As is the case with BA therapy, no previous research has studied the unique, component-specific effect of providing a clear treatment rationale. Providing this rationale may increase the patient’s motivation to exercise, which in itself may give a direct placebo-type antidepressant effect and/or indirectly reduced depressive symptoms following increased physical activity (which can be measured). This trial will be the first to study the component-specific effect of providing a clear treatment rationale in physical exercise therapy for depression.
In addition to studying the effects of Internet-administered physical exercise and BA - with and without providing a clear treatment rationale - and comparing them, this trial will include a depression relapse prevention program featuring cognitive behavioural therapy (CBT) components. Within 15 years, depression relapses may occur in as much as 90% of those experiencing an acute depression episode . Psychotherapeutic interventions have been shown to effectively reduce the risk of depression relapses , yet no previous study has examined whether this type of intervention can be administered via the Internet (see ). With there being ample evidence for the effects of Internet-based CBT on depression , a CBT-style relapse prevention program delivered via the Internet holds great potential. This trial will feature such a program, provided after the physical exercise or BA intervention.