Personal Informatics (PI) systems common trending theme is fitness, which in turn is a trending theme in human-computer interaction. These systems have been the focus of a handful of studies. So far, the research that has been conducted merely focuses on the technical details of such services and few investigate the longitudinal use of PI systems. Even though fitness is a popular area, still personal informatics systems designed for this purpose suffer from short-term use. Therefore, there is a need to design systems that encourages users for prolong use. The prolonged use of digital artifacts is an issue of sustainable interaction design. The purpose of this thesis is to explore the design space of personal informatics fitness systems through the lens of sustainable interaction design. This thesis aims at investigating motives and intentions behind the longitudinal use of personal informatics fitness systems. This thesis argues that by adopting the lens of sustainable interaction design we can find ways of designing PI systems with prolonged use for the users. Based on the findings the thesis ends by suggesting a guideline for designing personal informatics fitness systems which will hopefully help interaction designers and researchers alike.

Many people use personal informatics systems to gather personal behavioral data, make better decisions, and make changes to their behavior. While the proliferation of new products on the market makes collecting personal data easier, how to help people engage with these systems over a long period of time remains an open question. To uncover which features of personal informatics systems lead to engaging experience and long-term use, two user studies were conducted with people who use personal informatics systems to support or track behavior change. Baseline interviews were conducted and participants were asked to interact with personal informatics systems. Participants rated their experience both qualitatively and quantitatively and particularly in Study2, participants rated their experience with the system daily. At the beginning and at the end of each study, participants were asked to reflect on their physical activity levels and on their perceived behavior change at the end of the each study. The results were analyzed qualitatively and quantitatively and similarities and differences between the studies were exhibited. This research reveals that easy and instant access to data is critical, and feeling good and positive social outcomes of interaction will also support sustained product use. In addition, personalization of data is emerged to be an important expectation of the users. At the end, design implications for future personal informatics system are also offered.