While there are many benefits to regular engagement in physical activity, adults with intellectual and developmental disability (IDD) often do not engage in healthy levels of physical activity. Barriers, such as lack of accessible environments and or knowledgeable support staff, may limit participation in physical activity. The proposed study will utilize a mixed methods approach to look quantitatively at the relationship between how much time is spent in fitness classes, types of fitness classes, and physical fitness performance outcomes for adults with IDD as well as qualitatively at the qualities and practices of their personal trainer. We will also analyze a smaller sample of participants from the quantitative analysis and gather perceptions and experiences of those adults with IDD currently taking the fitness classes. This study will provide valuable data on fitness outcomes, a detailed insight into the practices of a personal trainer working directly with adult clients who have IDD, and experiences of the clients themselves. The results will help researchers develop a larger-scale study to investigate professional development models for training fitness professionals in local communities and the effectiveness of professional development trainings on client outcomes.