[Effect of an intervention in physical education classes on the reduction of sedentary behavior in adolescents].

This study aimed to analyze the effect of different intervention strategies in physical education classes on the reduction of sedentary time. This is a randomized, school-based intervention with factorial characteristics, carried out with freshmen high school students from 11 full-time schools, allocated in three intervention situations: (A) schools with two extra physical education classes per week; (B) schools with training and engagement actions for physical education teachers; (C) Schools with both A and B strategies; and (D) a group of control schools. Accelerometry was used to obtain the effect measure of the main outcome (sedentary behavior). Linear regression was used to analyze the time variation in sedentary behavior between baseline and post-intervention, as well as to analyze potential mediating factors of the relation between exposure and outcome. A total of 1,295 students participated in the study. Intervention B significantly reduced the time in sedentary behavior of boys (61.5 minutes, p < 0.01) and girls (34.8 minutes, p = 0.04) when compared to the control group, showing respectively medium (0.61) and small (0.32) effect size. The reduction in time in sedentary behavior among students in group B was significantly mediated by reduced lack of motivation (AMO) (boys c: -0.402, and girls c: -0.376). The offer of continuing training for physical education teachers proved to be a fundamental strategy to reduce the sedentary time of adolescents, which was mediated by the AMO reduction for physical education classes.