Core social network size predicts physical activity participation for fitness app users: The role of social support and social comparison

WeRun is a fitness plugin embedded in WeChat, the most widely used social networking app in China. WeRun can track and rank the step counts of the user and their WeRun friends. In addition, users can “like” their friends’ step counts. Drawing on the input-mechanism-output framework in mHealth, the current study connected the functions of WeRun to physical activity participation and examined the psychological mechanisms underlying the processes. Through a cross-sectional survey of Chinese WeRun users (N = 643), we found that the frequency of checking WeRun as well as users’ core network size (i.e., the number of friends followed on WeRun) positively correlated with physical activity participation. Both social support and social comparison mechanisms were explanatory of physical activity participation. Specifically, upward comparison was positively associated, and downward comparison was negatively associated with, physical activity participation. Upward comparison also mediated the relationships between the two user-app inputs (i.e., frequency of checking and core network size) and physical activity participation. Out of the three types of social support (i.e., informational, esteem, and companionship), only esteem support mediated the relationship between frequency of checking and physical activity participation. These findings reveal the theoretical mechanisms of fitness app functions and provide valuable insights for mHealth design.