To develop age- and sex-specific physical fitness reference standards and express the age- and sex-related differences using standardized effect sizes for Chinese children and adolescents. A total of 85,535 children and adolescents (48.7% girls) aged 7–18 years were recruited from six geographical divisions of China using a stratified randomized cluster sampling method. Seven physical fitness items including grip strength, standing long jump, 30-s sit-ups, sit and reach, 50-m dash, 20-s repeated straddling, and 20-m SRT were measured following a standardized procedure. Percentile curves for each physical fitness test were calculated using the LMS. Age- and sex-related differences were expressed as standardized effect sizes. We observed that the performance improved with age along with the analyzed percentiles in all tests. Boys had higher values compared to girls in all the physical fitness items except for sit and reach test, where girls showed better performance in all analyzed percentiles. Also, the sex differences increased with ages except sit and reach. There is a need for a differentiated approach in the physical education class in terms of adjustment of physical activity based on sex, level of fitness abilities in China.

To assess the association between body mass index (BMI) and physical fitness index (PFI) among children and adolescents in Xinjiang Uyghur Autonomous Region, China. In total, 17,618 children and adolescents aged 7–18 years from the selected region were enrolled in this cross-sectional study (8,800 boys and 8,818 girls). Participants were stratified by age and sex and divided into five groups by BMI percentiles: very low (BMI <5th percentile); low, (5th ≤ BMI < 15th percentile); normal (15th ≤ BMI < 85th percentile); high (85th ≤ BMI < 95th percentile); and very high (BMI ≥95th percentile). PFI was assessed by height, weight, and five health-related fitness indicators (grip strength, standing long jump, sit and reach, 50 m dash, and endurance run). BMI was significantly associated with PFI during adolescence (13–18 years) in boys and pre-adolescence (7–12 years) in girls. Between the ages of 13 and 18 years, an increase in BMI had a greater impact on PFI in boys than girls. PFI showed a parabolic curvilinear relationship with BMI. Children and adolescents in China’s Xinjiang Uyghur Autonomous Region with a normal BMI demonstrated good physical fitness. A BMI below or above the normal range may contribute to poor physical fitness. The relationship between BMI and PFI shows an inverted U-shaped curve.

We assessed trends in physical fitness by age group and nutrition status among children and adolescents in Xinjiang during 1985–2014. The data of 49,357 participants aged 7–18 were extracted in 1985, 1995, 2005, and 2014. Growth and nutritional status were defined using World Health Organization definitions. A physical fitness indicator (PFI) was calculated as the sum of six components measured in every survey. The relationship between body mass index (BMI) and PFI was investigated using nonlinear regression. Taking 1985 as a reference, PFI increased to 2 in 1995 and then fell sharply to −2.8 in 2005 and −3.8 in 2014. The prevalence of normal weight increased from 87.5% in 1985 to 89.4% in 1995 and then decreased to 75.2%, consistent with the change in PFI. The relationship between BMI and PFI showed an inverted U-shaped curve. The largest increment occurred in boys aged 13–15 and girls aged 16–18 during 1985–1995; the largest decline occurred in boys and girls aged 10–12 during 1995–2005. Our research provides a reference for local governments providing nutrition subsidies and projects in southern Xinjiang, indicating that greater attention is needed for children aged 7–12.

Background: Mental disorders among adolescents have become a worldwide public health problem. This study aimed to estimate the best combination of exercise time and screen time to promote the mental health of Chinese adolescents. Methods: Participants included 7200 Chinese adolescents aged 13–18 years from six regions of China. Screen and exercise time data were collected via a self-rated questionnaire. Psychological symptoms (e.g., often feeling depressed, school-weary) were evaluated with the “Multidimensional Sub-health Questionnaire of Adolescents”. Chi-squared tests and logistic regression analysis were conducted to investigate the differences in and correlations among screen time, exercise time, and psychological symptoms. Results: The overall detection rate of psychological symptoms among Chinese adolescents was 21.4% (22.1% for boys and 20.6% for girls). Psychological symptom detection rates were lowest among adolescents with 1–2 h/d of screen time (19.5%) and those with 30–60 min/d of exercise time (17.3%). Screen time > 2 h/d (OR = 1.38, P < 0.001) and exercise time < 30 min/d (OR = 1.62, P < 0.001) were positively correlated with psychological symptoms. Conclusion: Screen and exercise time are associated with psychological symptoms in Chinese adolescents. A combination of 1–2 h/d of screen time and 30–60 min/d of exercise time is provided as a reference for better mental health.

Background: The outbreak of COVID-19 has seriously threatened the health of people around the world. To prevent the spread of the epidemic, Chinese universities have implemented closed management of campuses. The implementation of restrictive measures has gradually caused changes in the quality of sleep and the psychological state of college students. In addition, college students are faced with the dual pressure of employment and study, and the psychological pressure is huge. Therefore, it is necessary to investigate sleep and depressive symptoms among college students. Methods: Using the method of stratified cluster sampling, 6695 college students were selected from three universities in Jiangxi, Anhui, and Xinjiang provinces from April to May 2022. The Chinese version of the Pittsburgh sleep quality index (PSQI) and the self-rating depression scale (SDS) were used for the survey. Hierarchical logistic regression analysis was used to analyze the relationship between the PSQI and the SDS. Results: Overall, during the outbreak of COVID-19, 69.0% of males and 73.5% of females had poor sleep quality among Chinese college students and the detection rate of depressive symptoms was 43.6% for males and 47.8% for females, respectively. Taking students with good sleep quality as references, after controlling for covariates, hierarchical logistic regression shows that Chinese college students with poor sleep quality have a higher OR value (OR = 12.0, 95%CI: 10.2~14.1, p < 0.001), especially in males (OR = 43.8, 95%CI:30.2~63.6, p < 0.001). For both males and females, the OR value of college students with the following characteristics was higher: rural college students (males, OR = 50.32, 95%CI: 32.50–77.93; females, OR = 8.03, 95%CI: 6.45–9.99), overweight college students (males, OR = 62.17, 95%CI: 19.47–198.53; females, OR = 16.67, 95%CI: 6.48–42.88), and college students drinking sugar-sweetened beverages (males, OR = 59.00, 95%CI: 36.96–94.18; females, OR = 8.16, 95%CI: 6.63–10.05) (p < 0.001). Conclusions: Poor sleep quality is associated with depressive symptoms among Chinese college students, especially college males. Our research suggests that it is necessary to consider the improvement of sleep quality and depressive symptoms among college students during the COVID-19 epidemic.