The global prevalence of overweight and obesity has doubled over the past 40 years and is increasing worldwide among children and adolescents [
1,
2]. Obesity leads to an increased risk of noncommunicable diseases, such as cardiovascular diseases, diabetes and cancer, and is associated with degenerative muscle and joint diseases as well as psychosocial, psychological and psychiatric consequences [
2‐
5].
In addition to the genetic predisposition, environmental factors, such as eating habits, physical activity, socioeconomic factors, environmental and cultural aspects play a central role in the multifactorial genesis [
6,
7]. This results in the relevance of multimodal therapy with the three basic components of nutrition, exercise and behavioral therapy [
6]. Social physical fear, body shame, stigmatization and harassment of adolescents with an increased body mass index (BMI) have a negative impact on sport commitment [
8‐
10]. The poor athletic performance leads to frustration, demotivation and further withdrawal from the athletic activity, and the joy of movement is lost [
11].
The positive effects of exercise programs for obese adolescents on a physical and psychological level have been confirmed by numerous studies [
12‐
14]. Therefore, under the guidance of physiotherapists they represent a suitable therapeutic measure for this target group. In addition to specialist knowledge of the musculoskeletal system, psychosocial strategies for behavior change must be considered as clinical competencies in physiotherapy. For this purpose, Deci and Ryan’s psychological concept of the self-determination theory (SDT) was scientifically examined [
15]. According to the SDT, experiencing autonomy, competence and social integration is an essential prerequisite for the development of intrinsic motivation. Intrinsic motivation is the most valuable form of motivation, which is expressed in completely internalized and self-determined actions. In contrast, the extrinsic motivation is an externally determined motivation. In between are further gradations on a continuum, such as the introjected motivation, which is characterized by self-control and the identified motivation, in which the importance of behavior for oneself is already conscious [
16]. Autonomy means the possibility to self-regulate one’s own actions, competence describes the ability to manage challenges, and social integration means having a close connection to other individuals and being a recognized member of a social group [
16,
17]. Promotion of motivation represents the advancement of these three basic psychological needs. A motivational process to increase physical activity with the support of coaches is associated with the prevention of obesity in adolescents [
18]. Positive and clear communication with adolescents and the well-being in a group make a decisive difference with respect to the development of intrinsic motivation for movement [
19]. Constructive feedback, active listening, humor and clarifying the relevance of the learning content play an essential role [
8]. The evidence of the practical implementation of the SDT was examined in different fields [
16,
20,
21]. So far, only a few study results have been available for physiotherapy regarding the practical implementation of the SDT and data for adolescents with obesity are missing [
15,
22].
The aim of this pilot study was to examine the effect of the implementation of motivational aspects based on the SDT in an 8‑week physiotherapeutic group training combined with a home exercise program that aimed to motivate obese adolescents to engage in physical activity. The hypothesis was that the motivation of the obese adolescents to move is generally low and that motivation to participate in exercise programs can be improved by the implementation of the SDT in physiotherapeutic group training.