In recent years, the practice of digital self-tracking has been the focus of much scholarly attention both within and outside of sporting contexts, and critical scholars have begun to take seriously the ways that individuals interact with, and are acted upon by, wearable self-tracking devices (e.g. Fitbits) and other types of digital health technologies (see Esmonde, 2018; Millington, 2016). Little attention has been paid, however, to the social dimensions of self-tracking, which is notable when we consider the proliferation of fitness apps that enable and, in some cases, actively encourage users to share the data produced while self-tracking. In this paper, I discuss preliminary findings from an ethnographic study of Strava – a popular social fitness app – and highlight both why and how runners use this particular web-based platform. In so doing, I draw attention to some of the ways that tracking the self socially can not only inform and influence how athletes think about health and the (in)active body, but can also invite noteworthy re-visionings of liminal, physical, and digital spaces.