RESUMEN
Youth obesity has been a pandemic for decades. One of its causes is a low level of physical activity. It is necessary to know the specific situation of adolescents and the factors that influence it in order to be able to act accordingly. The first aim of the current study is to create an explanatory model to establish the relationships between light physical activity time, light physical activity energy expenditure, screen time and social support. The second aim is to propose a theoretical model specifying the relationships between moderate-vigorous physical activity time, moderate-vigorous physical activity energy expenditure, screen time and social support. The study design was non-experimental (ex post facto), descriptive-correlational and cross-sectional. A total of 694 adolescents from the region of Soria (12-17 years) participated in the study. The instruments administered were the Four by One-Day Physical Activity Questionnaire, Parent Support Scale and Peer Support Scale. Two structural equation models were developed to analyse the relationships between the variables that comprised the explanatory models. The results show that social support had a negative influence on screen time in the proposed model in relation to light physical activity (r = -0.210; p ≤ 0.001) and in the proposed one regarding moderate-vigorous physical activity (r = -0.173; p ≤ 0.05). Social support was negatively related to light physical activity time (r = -0.167; p ≤ 0.05). Family support had a greater influence than did peer support. In conclusion, the models for light and moderate-vigorous physical activity are useful to describe the relationships between time, energy expenditure, screen time and social support.