Introduction: Sufficient physical activity (PA) is important for all aspects of health. Smartphone apps and the use of gamification, such as narrative-based augmented reality (AR), have a great potential to engage a variety of people in more PA. Zombies, Run! (ZR) is the world's most popular running exergame app and therefore a suitable model to understand what users find engaging. Objective: To understand people's motivation and experience of using a narrative-based AR exergame app ZR for PA. Materials and Methods: ZR users were randomly selected for interview from a quantitative ZR user's survey. Interviews which were guided by a semistructured topic guide were audio-recorded, transcribed, and analyzed using inductive and deductive thematic analysis. Results: Participants were 15 males and 15 females aged 16-53 years (mean = 36, SD = 10), from 13 countries, with the largest proportions from the United States (30%) and United Kingdom (23%). The majority (73%) used ZR while running, followed by cycling and walking. Four overarching themes that emerged were: "Reasons for starting and staying with ZR," "Preferred features," "Perceived effects of ZR," and "Pros and cons of the app." Sixteen subthemes included the attraction of gamification and narrative appeal, desire to add something fun to PA, or to distract from the negative physiological effects of PA. Users' favorite features were the feelings of immersion and presence through narrative, story line, and characters. The narrative motivated participants to engage in PA for longer sessions and encouraged long-term use. Conclusions: This study identified a number of factors that users found attractive in an AR running exergame, particularly narrative. Our findings suggest that ZR may engage people in exercise by modifying their perception of PA through a story line or narrative, dissociating the players from the effort of exertion. AR narrative-based apps may be an effective way of engaging people with health-related behaviors or habit-forming activities.
Keywords: Augmented reality; Exercise; Health; Leisure activities; Mobile applications; Obesity; Qualitative research; Sports; Videogames; Virtual reality.