Participation, upon medical advice, in some form of physical activity in order to manage a chronic illness does not come about spontaneously, especially when an individual has not been physically active prior to the illness in question. Our objective here is to analyse this process of commitment to physical activity by looking at 22 subjects diagnosed with type 2 diabetes, and who engage in physical activity firstly via a therapeutic education plan based upon Adapted Physical Activity (APA), through a hospital or health network, and thereafter, via patient group activities. Three phases of involvement can be identified: the first appears in the `disease trajectory,' the second opens an `APA practitioner career' to patients, whilst the third consolidates this `career' in a wider social setting. These three forms of commitment succeed each other along a line of progression over the course of which there is an increasing desire for independence from prescription medication, an increase in personal physical awareness, and a development of social networks.