While physical activity generally declines in middle-aged adults, group exercise participation among 40-64-year-olds is increasing. This rise may be due to the accessibility of online group exercise formats and their ability to reflect members' identities. This research explores how social identification processes facilitate participation in Zwift, an online group exercise platform. Seventeen Zwift participants aged 40-64 were recruited for three data collection stages: (1) an initial semi-structured interview on exercise history and Zwift usage; (2) a two-week post-exercise diary capturing social identification experiences; and (3) a follow-up interview to discuss topics from the first two stages. Data were analysed using abductive thematic analysis. Zwift supports three levels of social identity abstraction: (1) Identity Continuity, maintaining a cyclist identity through online cycling; (2) A Compatible New Identity as a Zwifter, formed through group interaction and social support; and (3) New Group Membership, developed through in-team belonging, recognition, and social status. Mid-life is a period of transition and identity change. Findings in this study suggest four ways that online platforms could facilitate social identification within online exercise platforms, namely (a) empower selection via perceived life-stage similarity and age, (b) enable ‘digital proximity’ via text chat and participant on-screen avatars, (c) enable the common fate of shared real-time exercise experiences, and (d) facilitate interaction and belonging via a pre and post-exercise ‘digital clubhouse’ via a social media page.