ObjectiveSocial isolation negatively impacts early-disease processes and long-term health. Individuals with chronic pain are more vulnerable to social isolation, which exacerbates symptoms. It is currently unclear whether: 1. group-based programs for chronic pain improve social isolation, 2. improvements in social isolation account for improvements in outcomes. This study involved secondary data analysis of participants in a 10-week mind-body physical activity program. We examined whether social isolation improved during treatment, and whether such improvements accounted for improvements in emotional and physical functioning. MethodsParticipants (N = 82) with chronic pain were randomized to a group-based mind-body physical activity intervention with (GetActive-Fitbit; n = 41) or without a Fitbit device (GetActive; n = 41). Participants completed self-reported measures of social isolation, emotional functioning (depression and anxiety symptoms), and multimodal physical functioning (self-report, performance-based, and objective). We used linear mixed effects modeling to examine pre-post treatment changes in social isolation and whether these changes accounted for improvements in emotional and physical functioning. ResultsBoth interventions were associated with significant and comparable improvements in social isolation from baseline to end of treatment, and improvements in social isolation accounted for significant improvements in self-reported emotional and physical functioning. ConclusionInterventions may target social isolation in chronic pain to optimize treatment outcomes.