Introduction
An increase in the prevalence of obese citizens as well as citizens with sedentary work and leisure activities is seen among the Danish population. Studies show that inactivity is associated with the development of obesity and obesity-related lifestyle diseases why physical activity is essential in reducing the risk of developing obesity-related lifestyle diseases. Preliminary initiatives in this area have not shown any noteworthy effect on the development of obesity or obesity-related lifestyle diseases. Therefore, development of effective health programs targeting changes in physical activity level is needed. The health program by the municipality of Aarhus, “Healthy lifestyle”, is targeted towards obese citizens in risk of developing obesity-related lifestyle diseases. A mini-evaluation of the program show that more than half of the participants only to some degree have acquired tools that makes them feel confident in being physical active post program. Previous intervention studies examining the use of activity tracking devices have shown promising results in increasing activity level and weight loss.

Objective
The objective of the thesis is to examine whether and how activity tracking devices potentially can support persistent behavioral changes in physical activity among obese citizens participating in the health program “Healthy Lifestyle” in the municipality of Aarhus. The aim hereby is to contribute with a number of recommendations for developing purposes of public health programs.

Method
The thesis is based on a theory interpretative case study of the “Healthy Lifestyle” program. Independent empirical material has been collected through focus group interviews based on overweight citizens in the “Healthy Lifestyle” program. Bandura’s Theory of Self-efficacy is used as a basis for a deductive analysis of the collected empirical material. A structured literature search has been conducted in PubMed, PsycInfo, Embase and Cochrane. The empirical material is used to discuss and validate the independently collected empirical material.

Results
Newer activity tracking devices contains a wide range of well documented techniques for behavioral change. The following potentials are associated with the use of activity tracking to support changes in physical activity level; self-monitoring, biofeedback, individual customization, individual goals and guidance, social support and sharing of data with relevant health professionals and/or other users. The following barriers are associated with the use of activity tracking to support changes in physical activity level; lack of user friendliness and cooperation across information technology solutions, low validity and reliability of measurements, high price level and unclear handling and use of sensitive personal data.

Conclusion
There appears to be generally good agreement between the results of the present interviews and the results of the present literature study. If the activity tracker is able to support the user's confidence in relation to change activity habits, can use potentially support persistent changes in physical activity among overweight citizens.