: As the proportion of older adults in Germany continues to grow, so does the need for physical activity as a strategy for health promotion. The purpose of this study is to gain insights into the belief system underlying older adults' physical activity and its interplay with motivation by integrating Theory of Planned Behaviour and Self-Determination Theory.: We conducted 20 semi-structured interviews with residents of Germany who were 65 years of age or older. Transcripts of interviews were analysed with a coding frame of deductive main categories and inductive subcategories.: Part of our results is a typology that divides our sample into four groups based on the intensity and perceived sufficiency of their physical activity. These groups mainly differ in their intrinsic vs. extrinsic motivation and how they deal with barriers to physical activity, i.e., control beliefs.: Messages to promote physical activity should be tailored regarding older adults' varying beliefs and motivation. To overcome barriers, intrinsic motivation plays a crucial role. Intrinsic motivation is closely linked to activities that are joyful and satisfy basic psychological needs. Moreover, it is important for older adults to be able to adjust their activities to age-related physical limitations and chronic diseases.
