Whereas running is inherently independent, it is often a social endeavor – conducted in groups and sustained by socially-derived motives. Based on this understanding, previous correlational research reveals that personal running identities are related to (but distinct from) runners' social identification with running groups (Strachan, Shields, Glassford, & Beatty, 2012). To better understand how group memberships impact personal running identities, the current online experimental study examined whether priming running group membership influenced self-reported running identity and intentions. One hundred and three running group members (Mage = 45.31; SD = 10.82; 63% female) were randomly assigned to read one of two vignettes that required them to imagine a training session where they were running (a) on their own, or (b) within their running group. Participants then reported running intentions and rated their personal running identity, before completing additional items (i.e., demographics, describing running group, and manipulation check). Whereas running intentions did not differ by condition, participants reported stronger personal running identities after imagining running with their group, p = .04. Follow-up analysis revealed that this result was moderated by sex, whereby the effect was primarily evident among female running group members. Although these findings are consistent with expectations for how group membership contributes to personal identities, they also support emerging results indicating that sex may shape how individuals connect to their groups (i.e., Gore, Bowman, Grosse, & Justice, 2015).