[Theory of change implemented in the program to promote physical activity "La Ribera Camina"]

To develop a theory of change of a program to promote physical activity in eleven health districts, in order to improve its design and plan its evaluation.

Four focus groups were carried out, to develop a participatory theory of change, to identify the expected changes (long, medium and short term) of "La Ribera Camina" program, according to the following stakeholders: primary healthcare professionals, local government representatives and community members. A thematic analysis was used to identify the actions to be taken to achieve these changes, as well as the difficulties and facilitators to enhance the sustainability of the program.

The identified changes were classified into four themes: 1) changes in physical and social health (improved physical condition, healthy habits, self-esteem and perceived well-being); 2) organizational and relational changes (better coordination between institutions); 3) specific changes to the program (incorporation of more "assets" and local associations, especially male participants, more trails and schedules); and 4) changes in the environment (improved trails' infrastructures and safety).

The theory of change allows to identify and classify the changes that are expected, the actions to be carried out and the links between elements of the program. This will serve as the basis for its evaluation. This methodology could be applied to other programs interested in incorporating intersectorality and community engagement in their design and evaluation.