Objective: To test the relationship between duration of physical exercise and sadness of middle school students, so as to provide enlightenment for students to participate in physical exercise when they are faced with sadness. Methods: Through the methods of multiple linear regression and regulatory effect test, data of 8 146 middle school students from China Education Panel Survey 2014-2015 were analyzed. Results: A negative correlation was observed between physical exercise duration and sadness of middle school students (r=-0.08, P<0.01); physical exercise duration showed significant negative main effect on depressive mood of middle school students (β=-0.05,P<0.01); the square term of physical exercise students shows significant curve correlation with depressive mood of middle school students (β=-0.04, P<0.05); physical exercise students had significant negative main effect on depressive mood of urban and rural middle school students(β=-0.04,-0.05, P<0.01); the square term of physical exercise duration does not show significant curve correlation with depressive mood of rural middle school students (β=-0.01, P>0.05), but showed significant curve correlation with depressive mood of urban middle school students (β=-0.06, P<0.01). Conclusion Physical exercise duration has threshold effect on relieving middle school students’ Sadness, while the threshold effect of rural middle school students physical exercise time disappears. Attention should be paid to the understanding of the relationship between physical exercise duration and sadness of middle school students.

Objective: To study the allocation of policy attention of life safety and health education in the Work Essentials of the Ministry of Education from 1987 to 2022 based on policy analysis, and to provide reference for the optimization of life safety and health education policy. Methods: The contents related to life safety and health education in the Work Essentials of the Ministry of Education from 1987 to 2022 were coded by content analysis method and analyzed quantitatively. Results: The attention of life safety and health education policies in schools in China could be divided into three stages: consolidation and improvement stage (1987-2000), reform and exploration stage (2001-2012), and deepening and improvement stage (2013-2022), with the attention intensity was rising as a whole. The government s policy on life safety and health education focused on health behavior and lifestyle (39.5% of the total reference point), safety emergency and risk avoidance (36.2% of the total reference point), mental health ( 11.9 % of the total reference point).The two fields of growth and adolescent health (8.1% of the total reference point),infectious disease prevention and public health emergency response (4.3% of the total reference point) paid less attention. The government had paid attention to 20 core points in the field of life safety and health education, and there were still 10 core points that had not been paid attention to. Conclusion The attention intensity of school safety and health education policy in China has been improved as a whole, and there are deviations in the policy attention at each stage.Limitations also include the inbalance of policy attention, lack of dynamic policy and the passivity of policy response;Life safety and health education in various fields of content and policy attention allocation direction is not comprehensive.It is suggested to stabilize the total amount of attention allocation on life safety and health education policy, to ensure balanced allocation, dynamic adjustment and pre judgment;More attention should paid on the comprehensiveness of contents in each aspects in policy optimization and adjustment.