Objective: To explore the association between mental health and muscle strength among Chinese adolescents aged 13- 18, providing a theoretical foundation and intervention strategies for mental health promotion. Methods: Data were obtained from the 2019 Chinese National Survey on Students Constitution and Health, including 98 631 Chinese adolescents aged 13- 18. Psychological distress was assessed by using the Kessler Psychological Distress Scale (K10), and mental well being was measured with the Warwick-Edinburgh Mental Well being Scale (WEMWBS). Based on the gender and age specific Z scores of various test items [grip strength, standing long jump, pull ups (for males), and sit ups (for females)], muscle strength index (MSI) was constructed to evaluate the comprehensive level of muscle strength in adolescents. According to the Dual factor Model (DFM) of mental health, participants were categorized into four groups:troubled, symptomatic but content, vulnerable, and complete mental health. Gender differences were analyzed by using Chi-square tests, trends were tested with Cochran-Armitage tests, and multinomial Logistic regression models were applied to assess associations between muscle strength and mental health among adolescents. Results: In 2019, 37.4% of Chinese adolescents aged 13-18 were reported of high mental distress, and 59.9% were reported of low mental well being. Boys had significantly lower rates of high mental distress (35.3%) and low mental well being (55.6%) compared to girls (39.4%, 64.3%), and the differences were of statistical significance ( χ 2=176.13, 780.42, both P <0.05). In 2019, the rate of complete mental health among adolescents showed a downward trend with increasing age ( χ 2 trend = 258.47) and a gradual upward trend with increasing muscle strength levels ( χ 2 trend =123.14)，and both boys and girls exhibited similar trends ( χ 2 trend =103.83, 168.46; 57.00 , 67.34) (all P <0.05). The results of the unordered multiclass Logistic regression model showed that after controlling for confounding factors such as age and gender, when the completely pathological group as a reference, for every 1 unit increase in MSI in adolescents, the likelihood of being in a completely mental health state increased by 29% ( OR = 1.29); for every unit increase in the Z-score for pull ups, the likelihood of being in a completely mental health state increased by 6% ( OR =1.06) among boys; for every 1 unit increase in sit up Z score, the likelihood of being in a completely mental health state increased by 19% ( OR =1.19) among girls (all P <0.05). Conclusions The mental health status of Chinese adolescents is not good enough. Muscle strength is positively associated with mental health.

Objective: To analyze physical fitness and health status and gender differences of middle school students among 5 minorities (Mongolian, Hui, Uyghur, Zhuang and Korean), and to provide the theoretical basis for the strategy formulation. Methods: The present data came from 3 waves of Chinese National Survey on Students Constitution and Health (2010, 2014, and 2019). According to National Standards for Students Physical Health (2014 Revision), excellent, and excellent good physical fitness and health status were defined. Cochran Armitage test was used to examine the trends of physical fitness and health status. Chi square test and Logistic regression were used to analyze the difference of physical fitness and health status by sex and survey year. Results: From 2010 to 2019, the excellent physical fitness and health status rate of Mongolian, Hui, Uyghur, Zhuang and Korean students increased from 1.8%, 0.7%, 0.3%, 0.5% and 1.3% to 4.3%, 2.8%, 1.2%, 1.3% and 3.5%, respectively. The excellent good physical fitness and health status rate of Mongolian, Hui, Uyghur and Zhuang students increased from 12.9%, 8.0%, 7.2 % and 8.4% to 24.7%, 20.1%, 12.6% and 19.8%( Z =6.15，6.71，4.12，3.06，5.26；11.88，13.42，6.70，11.08， P <0.05), respectively. In 2019, students aged 13 to 15 years showed higher proportion of excellent/excellent good physical fitness and health status than that of students aged 16 to 18. Boys were more likely to be in excellent/excellent good physical fitness and health status than girls from 2010 to 2019. The sex difference in excellent/excellent good physical fitness and health status narrowed during 2010 and 2019. Conclusion Physical fitness and health status of minority students improved while sex difference narrowed during last decade, but there is still a long way to reach the goal proposed by China. Targeted intervention should be proposed to promote physical fitness and health status in accordance with the developmental characteristics, especially for girls and students aged 16 to 18 years.

Objective:To analyze the association between the occurrence of spermarche and menarche and psychological distress among Chinese Han children and adolescents aged 9 to 18 years.Methods:Data were drawn from the 2019 Chinese National Survey on Students' Constitution and Health, and a total of 54 438 boys aged 11 to 18 years and 76 376 girls aged 9 to 18 years with psychological distress, spermarche/menarche records were included in the final analysis. The occurrence of spermarche/menarche was recorded by physicians, and psychological distress was classified according to the Kessler Psychological Distress Scale scores. The chi-square test was used to compare the difference between groups in the occurrence of spermarche/menarche, and the multinomial logistic regression model and stratification analysis was established to analyze the association between psychological distress and spermarche/menarche.Results:The incidence of spermarche/menarche in 2019 ranged from 6.3% to 96.5% for eight age groups of Chinese boys and 2.8% to 99.0% for ten age groups of girls. The rates of high psychological distress among boys and girls were 32.5% and 32.7%. Among boys aged 11 to 18 years, the rate of high psychological distress increased with age, with a trend test P<0.001, and the difference in the rate of high psychological distress between those who had and had not had their spermarche was not statistically significant in all age groups. Among girls aged 9 to 18 years, the rate of high psychological distress increased with age, with a trend P<0.001; the rate of high psychological distress was higher in the group with menarche at age 10 and 12 than in the group without menarche (all P<0.05). High psychological distress was positively correlated with spermarche among boys aged 13-15 years living in urban areas and hight level economic development areas ( OR=1.11, 95% CI: 1.02-1.21; OR=1.18, 95% CI: 1.06-1.32). Overall, high psychological distress was positively correlated with menarche in girls aged 9-12 and 13-15 years ( OR=1.33, 95% CI: 1.25-1.42; OR=1.22, 95% CI: 1.07-1.39). High psychological distress was positively correlated with menarche among girls aged 9-12 years living in different regions except for the Northeast region, in areas with different levels of economic development, and in urban and rural areas, in girls aged 13-15 years living in urban, central, and western regions, and in girls aged 16-18 years residing in the central region. Conclusions:This study found an association between the occurrence of spermarche/menarche and psychological distress among Chinese Han children and adolescents aged 9 to 18 years in 2019, which was particularly significant among girls aged 9 to 12 years and boys aged 13 to 15 years living in areas with higher levels of socioeconomic development.

Objective:To describe the status of physical fitness of children and adolescents aged 13-18 years in China in 2019 and analyze its association with psychological distress.Methods:Data were drawn from the 2019 Chinese National Survey on Students' Constitution and Health, and 90 633 Han children and adolescents aged 13-18 years were included. Physical fitness was evaluated by "National Students Constitutional Health Standards" (2014 revised edition). Psychological distress was classified according to the scores of the Kessler Psychological Distress Scale: ≤19, 20-24, 25-29, and ≥30 scores indicated no, mild, moderate, and severe psychological distress, respectively, with moderate and severe psychological distress collectively referred to as high psychological distress. The χ2 test was used to compare the distribution differences between boys and girls, the Cochran-Armitage test was used to analyze the trend, and the multinomial logistic regression in the mixed effect model was established to analyze the association between physical fitness and psychological distress. Results:In 2019, the unqualified rate of physical fitness among children and adolescents aged 13-18 years in China was 17.2%, and the prevalence of excellent and good physical fitness was 18.2%, which was lower among boys (15.9%) than girls (20.5%) with a statistically significant difference ( P<0.05). The excellent and good physical fitness rate showed a significantly decreasing trend with age (trend test P<0.05). The rate of high psychological distress among children and adolescents aged 13-18 years in China in 2019 was 39.3%, with boys (37.0%) having a lower prevalence than girls (41.6%), supported by a statistically significant difference ( P<0.05), and a decreasing trend with the degree of physical fitness was observed both in boys and girls (trend test P<0.05). The multinomial logistic regression model showed that the prevalence of moderate ( OR=0.83, 95% CI: 0.79-0.88, P<0.001) and severe ( OR=0.81, 95% CI: 0.77-0.86, P<0.001) psychological distress were both lower in children and adolescents with excellent and good physical fitness. Conclusion:The status of physical fitness and psychological distress of Chinese children and adolescents aged 13-18 in 2019 was not optimistic, with physical fitness showing a significantly negative association with psychological distress.

Objective:To analyze the regional inequality of height among Chinese Han students aged 7 to 18 years from 1985 to 2014.Methods:The Chinese Han students aged 7 to 18 years with complete basic information and height data from 30 mainland provinces (excluding Hong Kong, Macao, Taiwan and Tibet in China) were extracted as participants from 6 successive cross-sectional surveys of the Chinese National Survey on Student′s Constitution and Health (CNSSCH). After excluding extreme and illogical cases, a total of 1 495 182 students were included in the analysis. The data of gross domestic product (GDP) per capita of each province at each survey year were collected from the website of National Bureau of statistics of China. Mann-Kendall trend test was used to analyze the trend of mean height across years. Weighted linear regression model was used to analyze the association between mean height of students aged 7 to18 years and GDP per capita at provincial level. Height difference, height ratio, slope index of inequality (SII) and relative index of inequality (RII) were used to measure the height inequality by gender and age groups.Results:The mean height of Chinese Han students aged 7 to 18 years increased from 144.9 cm in 1985 to 151.8 cm in 2014 ( P<0.05). The height difference between urban and rural students in all age groups was reducing ( P<0.05). The height difference between urban and rural boys aged 13 to 15 years decreased from 5.3 cm in 1985 to 2.5 cm in 2014, and the difference between urban and rural girls aged 7 to 12 years decreased from 4.6 cm in 1985 to 2.4 cm in 2014. The mean height of students aged 7 to 18 years was positively associated with GDP per capita in all survey years for both genders ( P<0.001). Taking Shanghai and Guizhou as the representatives of economically developed and underdeveloped provinces, from 1985 to 2014, the height differences between two provinces were 6.8-9.2 cm, 8.0-12.4 cm and 6.3-8.8 cm for boys aged 7 to 12 years, 13 to 15 years and 16 to 18 years, respectively, and the height ratios were stable at 1.05-1.07, 1.05-1.08 and 1.04-1.05 respectively. From 1985 to 2014, the SII of mean height for boys in three age groups were 4.4-6.2, 4.9-6.7 and 2.5-4.7, respectively. The RII of mean height of boys in three age groups were 1.03-1.05, 1.03-1.04 and 1.01-1.03, respectively. In the same period, the SII of mean height for girls in three age groups were 4.2-6.2, 2.8-4.5 and 2.5-3.9, and the RII were 1.03-1.05, 1.02-1.03 and 1.02, respectively. Conclusion:From 1985 to 2014, the urban-rural inequality of height development among Chinese Han students aged 7 to 18 years was narrowing, but the socio-economic inequality of height persisted and remained at a relatively stable level.

Objective:To analyze the gender difference in secular trends of body height in Chinese Han adolescents aged 18 years from 1985 to 2014.Methods:Data were extracted from 1985, 1995, 2000, 2005, 2010 and 2014 Chinese National Surveys in Students' Constitution and Health. A total of 124 099 Chinese Han adolescents aged 18 years were included in the analysis. ANOVA test was used to compare the body height between different subgroups stratified by gender and the mean difference and ratio in body height were calculated. Quantile regression model was used to assess the association between body height and gender over time in the adolescents stratified by region or area.Results:The mean body height of adolescents aged 18 years increased significantly from 1985 to 2014 with the rate of 1.3 cm/decade in male adolescents and 0.8 cm/decade in female adolescents, and the highest increment occurred from 1995 to 2005 in both groups. Male adolescents were taller than female adolescents at each subgroup ( P<0.05). Gender difference in body height increased from 11.1 cm in 1985 to 12.6 cm in 2014 and ratio remained to be 1.07-1.08. The body height was taller in adolescents in urban area than in rural area ( P<0.05) and in northeastern China than in other regions ( P<0.05) in both male and female adolescents. The body height of obese male adolescents had been taller since 2000 and the body height of obese female adolescents had been taller since 2010 than other groups. When adjusted for urban-rural areas, region, socioeconomic status and nutritional status, the body height increased over time at P 5, P 25, P 50, P 75 and P 95 in both male and female adolescents, and the increments of gender difference in body height at different percentile ranged from 0.45 cm/decade to 0.57 cm/decade. When stratified by region, the gender difference in body height showed similar trend with total sample except P 5 and P 95 in northeastern China, the difference of increments were not significant. Conclusions:From 1985 to 2014, the gender difference in body height of Chinese Han adolescents aged 18 years increased, and male adolescents showed greater increase than female adolescents. Moreover, the adolescents in northeastern and eastern China had larger increment in body height. It is necessary to paid more attention to the adolescents in central and western China to promote their physical development.

Objective:To analyze the regional inequality of height among Chinese Han students aged 7 to 18 years from 1985 to 2014.Methods:The Chinese Han students aged 7 to 18 years with complete basic information and height data from 30 mainland provinces (excluding Hong Kong, Macao, Taiwan and Tibet in China) were extracted as participants from 6 successive cross-sectional surveys of the Chinese National Survey on Student′s Constitution and Health (CNSSCH). After excluding extreme and illogical cases, a total of 1 495 182 students were included in the analysis. The data of gross domestic product (GDP) per capita of each province at each survey year were collected from the website of National Bureau of statistics of China. Mann-Kendall trend test was used to analyze the trend of mean height across years. Weighted linear regression model was used to analyze the association between mean height of students aged 7 to18 years and GDP per capita at provincial level. Height difference, height ratio, slope index of inequality (SII) and relative index of inequality (RII) were used to measure the height inequality by gender and age groups.Results:The mean height of Chinese Han students aged 7 to 18 years increased from 144.9 cm in 1985 to 151.8 cm in 2014 ( P<0.05). The height difference between urban and rural students in all age groups was reducing ( P<0.05). The height difference between urban and rural boys aged 13 to 15 years decreased from 5.3 cm in 1985 to 2.5 cm in 2014, and the difference between urban and rural girls aged 7 to 12 years decreased from 4.6 cm in 1985 to 2.4 cm in 2014. The mean height of students aged 7 to 18 years was positively associated with GDP per capita in all survey years for both genders ( P<0.001). Taking Shanghai and Guizhou as the representatives of economically developed and underdeveloped provinces, from 1985 to 2014, the height differences between two provinces were 6.8-9.2 cm, 8.0-12.4 cm and 6.3-8.8 cm for boys aged 7 to 12 years, 13 to 15 years and 16 to 18 years, respectively, and the height ratios were stable at 1.05-1.07, 1.05-1.08 and 1.04-1.05 respectively. From 1985 to 2014, the SII of mean height for boys in three age groups were 4.4-6.2, 4.9-6.7 and 2.5-4.7, respectively. The RII of mean height of boys in three age groups were 1.03-1.05, 1.03-1.04 and 1.01-1.03, respectively. In the same period, the SII of mean height for girls in three age groups were 4.2-6.2, 2.8-4.5 and 2.5-3.9, and the RII were 1.03-1.05, 1.02-1.03 and 1.02, respectively. Conclusion:From 1985 to 2014, the urban-rural inequality of height development among Chinese Han students aged 7 to 18 years was narrowing, but the socio-economic inequality of height persisted and remained at a relatively stable level.

Objective:Using the Chinese National Survey on Students′ Constitution and Health data from 1985 to 2014 to analyze the trend of excellent and good physical fitness and health status among Chinese Han students aged 13 to 18 years and the related influencing factors.Methods:738 523 students aged 13 to 18 years with completed data of gender, age, urban and rural, physical form, vital capacity and physical fitness were selected from the six Chinese National Surveys on Students′ Constitution and Health. According to National Standards for Students′ Physical Health (2014 revision), the comprehensive scores and the prevalence of excellent and good physical fitness and health status were calculated (90.0-120.0 was classified as excellent, and 80.0-89.9 was classified as good). The trend of prevalence of excellent and good physical fitness and health status in different years and the corresponding differences among students with different characteristics were analyzed and compared. The log-binomial regression model was used to analyze related factors of physical fitness and health status.Results:From 1985 to 2014, the overall prevalence of excellent and good physical fitness and health status increased from 27.6% in 1985 to 35.6% in 1995, and then declined to 13.9% in 2005. In the 2010 and 2014 cycles, the prevalence increased steadily, at 16.5% and 19.1% respectively. Except for 1995 and 2014, the prevalence of boys was higher than that of girls ( P<0.001). The prevalence of students aged 13 to 15 was higher than that of students aged 16 to 18 ( P<0.001). Log-binomial regression model analysis showed that girls ［ PR（95% CI）=1.03（1.00-1.05）, P=0.021］, rural area ［ PR（95% CI）=1.09（1.07-1.12）, P<0.001］, 13-15 years old［ PR（95% CI）=1.89（1.84-1.94）, P<0.001］, eastern region［ PR（95% CI）=1.94（1.88-2.00）, P<0.001］, middle region［ PR（95% CI）=1.15（1.11-1.20）, P<0.001］, Exercise time ≥1 h/d［ PR（95% CI）=1.41（1.37-1.45）, P<0.001］, parents support participation in sports activities after school［ PR（95% CI）=1.10（1.06-1.15）, P<0.001］, TV time ≤1 h/d［ PR（95% CI）=1.26（1.21-1.30）, P<0.001］, playing video games, watching videos or e-books ≤1 h/d［ PR（95% CI）=1.05（1.02-1.09）, P<0.001］ were all related to the high prevalence of excellent and good physical fitness and health status. Conclusion:The prevalence of excellent and good physical fitness and health status among students aged 13 to 18 was changing between 1985 and 2014. Gender, age, area, physical exercise time, screen time for non-learning purposes, and parents′ attitudes toward students′ participation in physical activities were all related to the excellent and good physical fitness and health status of students.

Objective To analyze the secular trends and geographic disparities of all-cause mortality among Chinese adolescents aged 10-24 years over the period of 1953-2010.Methods Data were extracted from the Chinese National Census in 1953-2010.We calculated the all-cause mortality and annualized rates of the changes.Using the provincial gross domestic product (GDP) per capita as an indicator of regional socio-economic development level,we calculated the Wagstaff normal concentration indices for adolescent mortality.Results Over the period of 1953-2010,the general patterns of Chinese adolescent mortality appeared higher in males than those in females,higher in the 20-24-year-old than those in the 15-19 year-old and in the 10-14 year-old groups,higher in adolescents from the western than those in the eastern regions.The mortality of adolescents decreased from 554.6/100 000 in 1953-1964 to 55.7/100 000 in 2010 in males and decreased from 488.4/100 000 to 26.7/100 000 in females,respectively.The percentage of decrease for females (94.5％) was higher than that for males (90.0％).In 1981-2010,the highest annualized rate of decline for males was seen in Beijing (4.4％),with the lowest seen in Qinghai (0.1％).For girls,Hubei showed the highest annualized rate of decline (6.4％) while Qinghai the lowest (0.8％).Provinces that with higher mortality tended to have lower annualized rate of decline.The concentration indices for boys were-0.07 (95％ CI:-0.11--0.03),-0.13 (95 ％ CI:-0.18--0.08),and-0.16 (95 ％ CI:-0.22--0.10) in 1990,2000,and 2010,respectively,and were-0.07 (95％CI:-0.13--0.02),-0.18 (95％CI:-0.24--0.12),and-0.18 (95％CI:-0.26--0.09) respectively in girls.The indices among 1990,2000,and 2010 did not show statistically significantly differences,both for boys and girls (P＞0.05).Conclusions Over the half century,the mortality of Chinese adolescents showed dramatic decreasing trend.However,in terms of death rates,gender and geographic disparities were consistently seen in the adolescents.

Objective:To compare the probability of physical activity (PA) time ≥1 hour at school and influencing factors in students in China between 2010 and 2014.Methods:We used the data of 2010 and 2014 Chinese National Survey on Students’ Constitution and Health (CNSSCH). The surveys covered the Han students aged 9-22 years and Tibetan students aged 9-18 years (Tibet). The participants were primary school students (9-12 years old), junior high school students (13-15 years old), senior high school students (16-18 years old) and college students (19-22 years old). The probability of PA time ≥1 hour at school was compared using χ2 tests between 2010 and 2014 survey years. Log-binomial Regression was used to estimate the relative risk ( RR) for the probability of PA time ≥1 hour at school in different age groups. Results:The overall probability of PA time ≥1 hour at school in students aged 9-22 years was 20.5 % in 2010, and 23.8 % in 2014. The difference between 2010 and 2014 was significant ( P<0.001). On the whole, the probability of PA time ≥1 hour at school increased in the eastern, central and western areas in 2014 compared with 2010 ( P<0.05), and the increase range was highest in eastern area, followed by western area and central area ( P<0.05). The probability of PA time of 1 hour at school in all age groups increased in 2014 compared with 2010 ( P<0.05). The increase in the probability of PA time ≥1 hour at school was larger in primary school students than that in high school students and college students ( P<0.05). The probability of PA time ≥1 hour at school increased in all age groups in three areas, except in junior and senior high school students in the central area where the probability of PA time ≥1 hour at school decreased. The probability of PA time ≥1 hour at school in primary and junior/senior high school students in the eastern area had the greatest increase, but in college students it had the smallest increase in the three areas. From 2010 to 2014, the changes in the probability of PA time ≥1 hour at school in students in different provinces were quite different, especially in primary school students. The probability of PA time ≥1 hour at school in four age groups increased in only three provinces. With the probability of PA time ≥1 hour at school in primary school students as the reference, the RR in junior high students had no significant change between 2010 and 2014. The RR in senior high school increased from 0.34 (0.33-0.35) in 2010 to 0.36 (0.36-0.37) in 2014, and the RR in college students increased from 0.33 (0.32-0.34) in 2010 to 0.43 (0.42-0.44) in 2014. Conclusions:The probability of PA time ≥1 hour at school in all age groups increased in 2014 compared with 2010, but there were great differences among provinces. The findings of our study suggests that although the national policy played a certain role, the provinces should take specific measures to improve the probability of PA time ≥1 hour at school in students according to their own conditions. In addition, more attention should be paid to PA of older students.