Community capacity building is an essential approach for health promotion, combining a participatory approach with the view to community ownership. Little research focuses on practical capacity building strategies and monitoring. Our paper looks into involving stakeholders in facilitated group discussions as a specific strategy for fostering capacity building processes. These processes focused on physical activity (PA) promotion in two German communities (ACTION4men). Along the dimensions of capacity building suggested in literature (e.g., problem solving, resource mobilization, leadership), we implemented two participatory stakeholder groups (1/community). These groups were motivated to develop and implement PA interventions for men >50 years. For measuring capacity building processes, a semi-standardized monitoring instrument was used to document all group meetings. Additionally, we conducted semi-standardized interviews with group participants and drop-outs to capture their perspectives on capacity building. All documents were analyzed using thematic analysis. We successfully established stakeholder groups that planned and implemented a range of local measures meant to increase PA among older men. In one community, the process was sustainable, whereby the group continued to meet regularly over years. Capacity building was successful to a certain degree (e.g., regarding participation, problem assessment, and resource mobilization), but stalled after first meetings. Capacity building processes differed between the two communities in terms of leadership and sustainability. The developed interventions mainly addressed the access to organized sport courses, rather than tackling walkability or active transport. The theoretical capacity building approach was successful to develop and implement programs aimed at promoting PA. The actual capacity building processes depend upon the composition of stakeholder groups and inherent power relations.