Today's consumer-facing activity trackers, such as fitness wristbands and smartwatches, often hold the promise of improving users' health, yet problems in user interaction with activity tracking technology, such as low user adoption, short-lived use, and limited user engagement, undermine the potential health benefits. In this dissertation, I tackle these problems by developing a comprehensive understanding of non-patient healthy activity tracker users' personal health information management (PHIM) with the data generated by their devices, an essential component of long-term user interaction with activity tracking technology.

Building on personal information management (PIM) theories and activity tracker user research, I present results from a web survey study and an in-depth interview study that jointly examined healthy activity tracker users' PHIM behaviors with data generated by their devices. Major findings include: the identification of healthy activity tracker users' health/fitness-related needs and information needs; an in-depth portrayal of their PHIM, covering the spectrum of PHIM tools they used, the six types of PHIM activities they performed, as well as the concurrent and subsequent PHIM practices they engaged in; and the depiction of the ways their needs were met, partially met, or unmet by their activity tracking technology use and relevant PHIM.

This dissertation contributes to existing research in information science, human-computer interaction, ubiquitous computing, and health informatics at empirical, theoretical, and methodological levels. First, I contribute empirical updates to both activity tracker user research and PIM research by examining healthy activity tracker users' PHIM. Second, I generate practical design implications for future activity tracking technology to better support PHIM based on my empirical findings. Finally, I reflect on my enhanced participant-driven photo elicitation techniques and provide methodological recommendations for future qualitative research to adopt the method.