Sport and exercise therapy for the treatment of major depressive disorder (MDD): Five guiding principles

Sport and exercise therapy is an effective alternative therapy to treat major depressive disorder (MDD). Most previous research, however, only examined single exercise prescriptions and compared these to pharmacotherapy and/or (placebo) control conditions. As a consequence, the current state of scientific research is dominated by aerobic exercise interventions, mostly based on “easy-to-control” study protocols, showing that running or jogging on treadmills are effective physical activities to reduce depressive symptoms. Nevertheless, we argue for the combination of aerobic exercises with other sport and exercise interventions embedded within a continuum of behavioral healthcare measures to follow a resource-oriented approach. Combining different kinds of physical activity with low and high intensity seems to better resemble contemporary approaches when treating MDD in an outpatient psychiatric setting, because today, day care clinics offer a variety of different sport and exercise courses. In this commentary, we propose five guiding principles to consider when designing combined sport and exercise interventions for the treatment of MDD. Correspondence to: Matthias Weigelt, Department of Sport & Health, University of Paderborn, Warburger Str. 100, 33098 Paderborn, Tel: (0049)-05251-60-5300; E-mail: matthias.weigelt@uni-paderborn.de


Introduction
Major Depressive Disorder (MDD) presents a major challenge for public health care systems and social well-fare around the world [1]. In fact, it is one of the most common psychiatric disorders of today, as approximately 350 million people are suffering from MDD [2]. In Germany, for example, the lifetime prevalence rate is suggested to be about 15% to 20% in the general population [3], while the 12-month prevalence rate in people aged 18-65 years is about 11% [4]. Trusting earlier projections, MDD is becoming one of the most significant illness burdens worldwide, being only second to coronary heart disease [5]. Therefore, researchers and clinicians have become increasingly interested in therapeutic measures and interventions of MDD, which go beyond common first-line therapies like prescribing only antidepressant medication. Because there is no single treatment being similarly effective for every patient [6], alternative therapies for MDD must be considered more seriously. Sport and exercise therapy is such an alternative therapy [7]. Its effectiveness has been evaluated in a number of meta-analysis and reviews [8,9]. This commentary focuses on the question which kinds of exercise prescriptions should be considered for the effective treatment of MDD in sport and exercise therapy.
Most of the studies supporting the effectiveness of sport and exercise therapy in the treatment of MDD looked at aerobic exercises, such as walking or jogging on a treadmill [10], or exercising on the bicycle ergometer [11]. For example, Blumenthal et al. [10] found similar positive effects in terms of remission rates for exercise therapy (i.e. 45 minutes walking on a treadmill, three sessions per week, for 16 weeks) and pharmacotherapy (i.e. antidepressant medication; sertraline, 50-200 mg daily, for 16 weeks), as compared to a placebo control group. They suggested that aerobic exercise may be similarly effective than pharmacotherapy, a notion, which has been supported in other recent studies [12,13]. Moreover, Mota-Pereira et al. [14] were able to show, that a 12-week intervention of aerobic exercise can lead to significant improvements of depression parameters, even in treatmentresistant patients with MDD.
Much less studies have investigated other kinds of exercise prescriptions. Among the few exceptions are investigations on the effectiveness of strength and resistance training [15,16]. Singh et al. [16] reported greater effects for weight training with high vs. low intensity (i.e. 45 minutes, three sessions per week, for eight weeks). Interestingly, such strength and resistance training may be as effective as aerobic exercise: When comparing both intervention strategies, Doyne et al. [17] found similar effects for running vs. weight lifting with respect to the reduction of depressive symptoms. This finding already suggests that different physical activities may be of similar efficiency.
When taking a closer look at the empirical investigations on the effectiveness of sport and exercise therapies, it becomes obvious that study protocols most often compared a single, specific kind of exercise prescription (mostly aerobic exercise) with antidepressant medication and/or a (placebo) control condition. Yet, exercise prescriptions combining different kinds of physical activity, including body-andmind oriented interventions, have not been investigated systematically. As a consequence, research has mainly addressed the affective symptoms of MDD, whereas the benefits of physical activity on other facets of the mental illness, such as psychomotor symptoms, cognitive deficits, and (psycho-) social deprivation, have been largely ignored. We argue that this paradigmatic approach to only examine single exercise prescriptions has led to a skewed picture of the effectiveness of sport and exercise therapy on MDD -a picture in favor of aerobic exercise, mostly based on "easy-to-control" study protocols, like running or jogging on treadmills. Combining aerobic exercises with different kinds of physical activity, however, seems to better resemble contemporary approaches when treating major depression in an outpatient psychiatric setting, because today, day care clinics (almost always) offer a variety of different sport and exercise courses. Among these activities are dance therapy, weight training, game sports, but also body-and-mind oriented interventions like tai chi, qigong, progressive muscle relaxation (PMR), and so on. Most often, these are not prescribed to patients on a scientific basis, but rather on the financial, personal, and organizational constraints of the clinic, which restrict the staff support, the kinds and total number of courses, the venue, the equipment, etc. In the following, we propose five guiding principles to design combined sport and exercise interventions, understood as a combination of aerobic exercises with different kinds of physical activities (including body-and-mind oriented interventions), for the treatment of MDD in the outpatient psychiatric therapy setting. The benefit of combining different physical activities is that other facets of the mental illness can be treated in the alternative therapy, which may not be addressed by aerobic exercise only. Thereby, the aim is to attend to the complex interaction of social, psychological, and biological factors of the disorder from a multi-professional perspective. This should pave the way for disorder-specific sport and exercise therapy programs in the future.

Promote the spontaneous initiation of actions and cognitive flexibility
In order to address not only the affective symptoms of MDD, sport and exercise therapy should also focus on psychomotor symptoms and cognitive deficits by including physical activities that require the spontaneous initiation of actions and promote cognitive flexibility. The goal should be to promote the engagement and spontaneity of the MDD patients, and not their strategies of error avoidance. Most suitable are such activities of game play in which patients must react quickly to changes of conditions and to flexibly adapt to new situation, such as in many forms of small-sided games and coordination drills. The correct timing of actions (and reactions) requires differentiating between relevant and irrelevant stimulus information and thus, addresses specific deficits in information processing. Each game or drill can be made more complex to increase the cognitive effort. Information processing can be enhanced by providing patients with explicit strategies to change the focus of attention, for example, from a narrow focus to a wide focus, and vice versa. Activities challenging patient's motor coordination skills will also draw attention away from negative cognitions and interrupt negative thought processes, which are typical symptoms of MDD. Here, sport psychology offers many exercises to train the focus of attention. These kinds of activities (e.g., small-sided games, coordination drills) provide MDD patients with the opportunity for positive experiences in otherwise neglected areas of behavior. Also, communicating and cooperating in a group setting provides social stimulation and social support, and creates situation in which they can reflect on their social behavior. All of these aspects seem to be positive side-effects of such activities [18,19].

Allow for mistakes and make them part of the learning process
Based on their cognitive distortions, MDD patients tend to overestimate mistakes and to excessively blame themselves for making errors. In order to avoid mistakes, they (often) become more and more inactive, which further manifests the depressive symptoms. Another task of sport and exercise therapy is therefore to select activities for social settings in which mistakes are encouraged and are viewed as a positive (or at least necessary) part of the learning process. Again, small-sided games, but also different forms of cooperation and interaction exercises, can be implemented. Especially, such activities should be chosen for the exercise interventions in which mistakes come without much consequences and can be compensated quickly by the change of play and (possibly) additional rules for compensations (e.g., badminton with slow-flying shuttlecocks or table tennis with bigger ping pong balls). This enables patients to commit mistakes in the first place, to come up with realistic estimates of the consequences of mistakes, and to better reflect on their own attribution tendencies. It opens up the opportunity for a more realistic evaluation of causal relationships and a re-appraisal of situational conditions, which may in turn reduce helplessness and negative cognitive schemata.

Improve body awareness and the sensation of bodily states
Typical psychomotor symptoms of MDD patients are limitations in their mobility and body awareness, as well as a slowing of movement. This results in a more general regression of motor coordination skills. Sport and exercise therapy can be used to stop this negative trend. Research on embodied cognition shows the close link between body posture and affect [20]. Thus, changing patient's body awareness and teaching them to attend to their body posture seems to be a promising approach to change their affective state. Sport and exercise therapy can be used to improve body awareness (e.g., yoga, tai chi, or qigong) and motor coordination skills (e.g., therapeutic climbing, therapeutic boxing). Patients (re-)gain knowledge about the functional aspects of their body and become aware of the positive effects of body-andmind oriented therapeutic interventions. The goal is not to increase the physical fitness of the patients, but rather to improve their (conscious) sensation of different bodily states. Here, different relaxation techniques (e.g., progressive muscle relaxation, autogenic training, varieties of meditation) should also be considered. These exercises can be further combined with exercises from mindfulness-based cognitive therapy [21].

Build up physical activity as a positive experience
It is obvious that sport and exercise therapy provides for a good measure to build up physical activity, especially when the individual preferences of MDD patients are taken into consideration for scheduling exercise interventions. In the same way as there is no single treatment of antidepressant medication that is similarly effective in every patient [6], there is no single exercise of similar benefit for the variety of depressive symptoms. Therefore, exercise intervention programs should be tailored to meet the individual needs of MDD patients. Here, the challenge is to combine different exercises and intensity levels (cf. physical activity and dose-response effects [22], which will suit a particular patient and keep her/him motivated throughout the therapy and beyond remission). It is important to avoid exertion and overtraining, especially in the beginning, in order to keep drop-out rates low and to generate positive performance experiences, which can also be used in other psychotherapeutic contexts. Patients can monitor the relationship between physical activity, motivation to exercise, and emotional states, while writing an activity diary. This will help them to better understand distinct changes of emotional states, based on the physical exercise performed, and to build up physical activity as a positive experience. less stress tolerant and experience large difficulties to cope with the demands of daily life [23]. This often results in withdrawal tendencies, a lack of self-esteem, and inactivity, which further manifests the depressive symptoms. Sport and exercise interventions offer a good setting to build up and improve coping skills, as well as self-efficacy. It is therefore important to educate patients with self-regulation strategies. Body-and-mind oriented relaxation techniques, like progressive muscle relaxation (PMR), autogenic training, or varieties of meditation, offer the opportunity to acquire coping strategies in a protected environment. Physical activities will also benefit self-efficacy and self-esteem. Here, aerobic exercise and strength training can be used to cope with challenging situations. For example, to reach own goals in sport and exercise therapy (e.g., running an intended distance, completing a workout) will increase the self-efficacy of patients, which can be transferred into other areas of life. The systematic increase of the intensity level (e.g., running distance, number of repetitions, weight lifted, duration of training, etc.) will further help to build up coping skills and to promote self-efficacy and self-esteem. Once established, clinicians and therapists can use these coping strategies in complementary psychotherapy settings and transfer them into everyday life to support patients in the management of their daily activities [18].

Concluding remarks
Together, these guiding principles should be considered when designing sport and exercise therapy programs for the treatment of MDD, which are oriented at the disorder-specific symptoms of the individual patient, or of groups of patients. Moreover, considering individual preferences for certain physical activities, may enhance motivation and reduce drop-out rates. Of course, it requires a more detailed (psycho-) diagnostic to identify the specific symptoms of the disorder, before alternative therapy interventions can begin. But it may be more beneficial than first-line pharmacotherapy in the long run, because it addresses facets of the disorder, which cannot be treated by prescribing antidepressant medication only. The same is true for single exercise interventions that are based on aerobic exercise only. Instead, combined intervention programs allow for the integration of various elements from psychotherapy into sport and exercise therapy, and at the same time, to use specific effects of sport and exercise therapy in complementary psychotherapy settings. From a multi-professional perspective, it thus brings together different available resources in the day care clinic to attend to the complex interaction of social, psychological, and biological factors of the illness.
The guiding principles presented are formulated in rather general terms. They can be adapted and filled with specific content, depending on the constraints of the day care clinic to improve the efficiency of sport and exercise therapy as an alternative therapy in the outpatient psychiatric setting. Instead of focusing (mainly) on aerobic exercise only, research agendas should attend to combined programs, which include aerobic exercises and other kinds of physical activity, and evaluate their effectiveness. This may provide a new picture of the effectiveness of different kinds of physical activity (and combinations thereof) for the treatment of MDD that go beyond single exercise prescriptions in sport and exercise therapy.