Objective: To explore the screen related sedentary behavior among senior primary school students in Beijing and to analyze the influence of psychosocial determinants and nutrition related knowledge on the behavior. Methods: In January 2020, a total of 1 316 students in grade 4-6 from two primary schools in Beijing were selected. Information on video viewing (watching TV or playing video games), self efficacy, habit strength, nutrition related knowledge, outcome expectation and the capacity to persist toward goal attainment were collected through questionnaires. Disordered multi classification Logistic regression and random forest algorithm were used to analyze the influencing factors. Results: The frequency of screen related sedentary was 5.0 (3.0, 10.5) times/week, and the duration was 37.5(9.6, 97.5) min/d in senior elementary school children. The results of disordered multi classification Logistic regression showed that the capacity to persist toward goal attainment, nutrition related knowledge, habit strength, self efficacy and gender positively correlated with the frequency of screen related sedentary ( OR =1.6, 1.7, 4.9, 4.2, 1.5 ), while the nutrition related knowledge, habit strength, self efficacy, outcome expectations, grade and gender positively correlated with screen time ( OR =1.7, 5.6, 5.7, 1.6, 1.6, 1.7)( P <0.05). Random forest regression tree model showed that the top four influencing factors on screen related sedentary frequency were self efficacy, the capacity to persist toward goal attainment, habit strength and nutrition related knowledge and the top four influencing factors on screen time were self efficacy, outcome expectation, nutrition related knowledge, habit strength. Conclusion Screen related sedentary behavior is prevalent among senior primary school students in Beijing. Health education should be strengthened regarding influencing factors of screen related sedentary behavior.

Objective: The association of self efficacy, habit strength, goal intention and outcome expectation with the consumption of snack in senior primary school students were investigated, providing evidence for the application of psychosocial determinants based on Social Cognitive Theory in children s nutrition education. Methods: A total of 1 353 students, 10-12 years old, participated in this study. Participants completed questionnaires for assessing self efficacy, habit strength, goal intention, outcome expectation and snack consumption in January 2020. Results: Average times of snack consumption among primary school students were 5.0 (3.0, 8.5) times per week, and the snack intake were 4.0(0.9, 22.9)g/d. The outcome expectation score was -1.0(-2.0, -1.0 ) points, while the score of children s snack related selfefficacy was (4.3±0.9) points, habit strength score 1.0(1.0, 3.0) points, and the goal intention (4.2±1.2) points. Students with higher snack intake showed lower scores in outcome expectation, self efficacy and goal intention( t=-9.0, 6.8, 5.2, P <0.01). Logistic regression showed negative association between outcome expectation and self efficacy factors with snacking behavior( OR =0.7, 0.8, respectively), as well as positive association between habit strength and snacking behaviors( OR=1.3, P <0.05). Conclusion The evidence indicated that self efficacy, habit strength, goal intention and outcome expectation are associated with child s snack consumption, and can be used as theoretical foundation for child snack consumption education.