Using self-contained units to characterize the key elements of some domains such as education and science has given autonomy and ease of managing resources to end users. In order to apply this concept to the physical exercise environment, this paper shows how to represent teaching for the proper use of the available machines in a public outdoor gym; such units minted under the title of physical activity digital objects. This representation allows building a repository for storing and retrieving these units, to form complete elements such as exercise routines.