The present research study's main objective was to find out whether there is a relationship between the body mass index (BMI) and the psychological aspects related to motivation, needs such as autonomy, competence, and social relationships, and the intention of being physically active in Physical Education students in Primary and Secondary Education. To achieve this, a total of 574 students (mean = 13.66; standard deviation = 1.96) participated in this study, to whom a series of questionnaires was administered once permission had been obtained from the centers the students attended, alongside the latter's acceptance to participate in the study. The main results showed that the students with a higher BMI were those who had lower self-determined motivation values with regard to the three basic psychological needs observed and the intention of physical activity. In turn, our differential analysis identified that the students attending Primary Education had lower values of BMI, motivation, and intention to be physically active than the students attending Secondary Education, without finding differences based on the gender of the participants. The need to keep on investigating this topic is consequently gathered, using direct techniques for measuring BMI or proposing mixed research designs.
Keywords: autonomy support; educational stage; gender differences; physical activity; physical education.