Anorexia nervosa (AN) is the mental illness with the highest standardized mortality rates. Not only restrictive eating behavior, low body weight, and fear of weight gain, but also early onset and chronic somatic and mental complications make it a very dangerous disease that has not yet been fully understood. Up to 80% of AN patients engage in high levels of physical activity (PA), which leads to an even larger imbalance of body weight. PA in AN is complex and cannot be reduced to a conscious

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... ion with the aim of losing weight. There are several forms of manifestations, multiple definitions, and various explanations of the origin. Additionally, there are many severe complications as consequences of PA in AN. These complications include, for example, longer duration of the illness, longer treatment durations, higher relapse rates, and more psychiatric comorbidities. Thus, the quantification of PA in AN is important. In literature PA in AN is most often carried out through subjective methods such as questionnaires, self-ratings, or interviews. Unfortunately, the precision of these methods is not very high. However, accelerometry is an objective method, which measures PA exactly through the assessment of triaxial acceleration of the body. The aim of this study was to establish accelerometry as a method of PA assessment in AN and to evaluate its feasibility in a pilot study. Therefore, the focus of this thesis lies on the methodology. To establish accelerometry in AN we concluded all literature that measured PA in AN with accelerometry in a systematic review. Subsequently, in the ANEX pilot study we measured PA in AN with the ActiGraph in 13 outpatients and 12 inpatients. The inpatients have been followed-up one month after treatment. Moreover, we assessed selfperceived PA with questionnaires as well as eating disorder pathology, stress, and depression. Many AN patients refused to participate, and in the ANEX pilot study we tried to determine the reasons for this.