Abstract Depression severely affects the healthy development of adolescents and has become a major public health challenge in China. The outbreak and normalization of COVID-19 have posed a serious challenge to the prevention and treatment of depression in adolescents. Given the characteristics of adolescent physical and mental development and depression pathology, the prevention and control of depression in adolescents should be shifted to an earlier stage. "Screening and dynamic monitoring" should be an important way to shift the focus of prevention and control of depression in adolescents. "Population based prevention" should be an important guarantee for achieving the shift toward early prevention and control of depression in adolescents, which builds a solid barrier for the mental health protection and promotion among Chinese adolescents.

Objective: To understand physical activity status and its relation with cardiopulmonary endurance among Chinese children and adolescents, so as to provide reference for cardiopulmonary endurance improvement and intervention of Chinese children and adolescents. Methods: During September to November 2018, a stratified cluster sampling method was used to select 4 269 children and adolescents aged 7-18 years in six major regions of China, 20 m shuttle run test and physical activity were assessed. Results: Average duration for daily lowintensity physical activity among boys was (31.49±30.01) min, for moderate to vigorous physical activity (68.37±46.50) min. Average duration for low intensity physical activity among girls was (34.02±31.58) min, for moderate to vigorous physical activity was (63.02±44.91) min. The number of 20 m shuttle run test for boys reached ( 36.17 ±21.94) times, and the maximal oxygen uptake per minute was (44.51±5.05) mL/kg; the number of 20 m shuttle run test for girls reached (26.59±12.56) times, and the maximal oxygen uptake per minute was (41.99±5.29) mL/kg. There were statistically significant differences in the number of 20 m shuttle run test and maximal oxygen uptake across age groups in boys ( F= 589.37 , 152.79, P <0.01), as well as that in girls ( F=305.21, 1 032.46, P <0.01). The proportion of boys and girls who met moderate to vigorous physical activity standard was 49.24% and 42.92%, respectively. Linear regression analysis showed that there was a significant positive correlation between the duration of moderate to vigorous physical activity and maximal oxygen uptake ( β=0.11, P ＜ 0.01). Conclusion There is a significant correlation between moderate to vigorous physical activity with cardiorespiratory endurance among Chinese children and adolescents. Higher level of moderate to vigorous physical activity is important to help improve cardiopulmonary endurance among children and adolescents.

Objective: To understand the relationship between family environment and depressive symptoms among adolescent, and to provide a reference for adolescent mental health promotion and intervention. Methods: From September to December in 2021, a questionnaire survey on family environment and depressive symptoms was conducted among 8 102 middle school students by random cluster sampling method in Shanghai, Urumqi, Changsha and Kunming. The Chi square test was used to compare the depression status of students in different family environments. Multivariate Logistic regression analysis was used to explore the relationship between family environment and depressive symptoms. Results: The detection rates of possible depression, likely depression and severe depression in adolescents were 11.2%, 5.9% and 8.4%, respectively. There were significant differences in the detection rate of depression by gender, academic period, urban and rural areas, family forms and only child statu( χ 2=87.60, 27.19, 6.65, 45.59, 4.78, P <0.05). Logistic regression analysis showed that adolescents in single parent families ( OR =1.45) and reorganized families( OR =1.69) were positively correlated with the occurrence of depressive symptoms compared with those in nuclear families( P <0.01). Conclusion Compared with nuclear families, the risks of adolescent depressive symptoms in single parent families and reorganized families are higher. Attention should be paid to the mental health education of teenagers from single parents and reorganized families to ensure the development of their physical and mental health.