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

The present study aimed to examine the effects of social networking functions of fitness apps on users' physical activity participation. Drawing on the input-mechanism-output framework in mHealth, this study connected the functions of a Chinese fitness app (WeRun) to users' step counts tracked by the app and examined the psychological mechanisms underlying the processes. Through a cross-sectional survey of 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. Social comparison mechanisms were explanatory of physical activity participation, but social support was not. 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. These findings reveal the theoretical mechanisms of fitness app functions and provide valuable insights for mHealth design.