This study aimed to investigate the relationship between homeostatic model assessment of insulin resistance(HOMA-IR), body composition and physical exercise of adolescents.

A total of 264 students aged 10-16 from No. 7 middle school(ordinary middle school group) and Jining Sports Training Center(sports school group) were randomly selected as the research subjects. During the baseline period, height, weight, blood pressure, heart rate, waist circumference, hip circumference and other data were collected through physical examination. Fasting blood glucose(FBG) and insulin(INS) levels were measured, self-reported dietary information(frequency of sweets, carbonated drinks, and milk intake), time spent using electronic devices, and nighttime sleep time were collected through questionnaires. During the follow-up period after 1 year, the data of body composition weight, skeletal muscle mass, body fat mass and body fat percentage were measured. The correlation between HOMA-IR and body composition was analyzed by single factor linear regression model. The Regression analysis of long-term physical activity and physical activity in general secondary schools of both groups were taken as the dependent variable, and the group was taken as the independent variable, age, sex at follow-up and data at baseline were included as covariates in the model.

A total of 264 students participated in the data collection in the baseline period and the follow-up period. Among them, 154 students in the ordinary middle school group participated in physical exercise activities inside and outside the school freely; 110 students in the physical education school group, strictly participate in different types of school physical training, from the baseline period to follow-up period to maintain regular physical exercise. The body mass index(BMI), INS level and HOMA-IR of the students in the sports school group were lower than those of the students in the ordinary middle school group at the baseline and follow-up periods(all P < 0.005). HOMA-IR was positively correlated with BMI, waist circumference and body fat rate in both groups(all P < 0.001). Models of HOMA-IR, INS level, BMI, waist circumference, and body fat percentage were used to evaluate the effects of age, gender, and body fat percentage on the outcome of the two groups of students, and self-reported diet(frequency of sweets, carbonated drinks, and milk intake), screen time, and night-time sleep, adjusted for body fat percentage, the remaining models also need to be adjusted for baseline dependent variables. The results showed that long-term regular physical exercise was negatively correlated with HOMA-IR, INS level, BMI, waist circumference and body fat rate during follow-up period(all P < 0.005). Students in the general secondary school group were further divided into a physical activity subgroup of 27 and a non-physical activity subgroup of 127 based on self-reported physical activity in questionnaires during the baseline and follow-up periods, after adjusting the influencing factors, it was found that physical exercise was also negatively correlated with HOMA-IR, INS level, BMI, waist circumference and body fat rate during the follow-up period(all P < 0.005).

Long-term regular physical exercise can improve BMI and insulin sensitivity in adolescents, which may help to prevent and improve excessive fat accumulation and insulin resistance.

To investigate body composition and associated factors in adolescents undergoing long-term regular sports training.

This prospective longitudinal cohort study employed convenience sampling to recruit adolescents receiving structured athletic training at Jining Sports Training Center in June 2023. Baseline measurements included height, weight, body mass index (BMI), blood pressure, heart rate, waist circumference, and hip circumference. Questionnaires assessed sleep duration, screen time, and household income. Follow-up measurements in June 2024 repeated these assessments while adding bioelectrical impedance analysis for body composition (lean mass, skeletal muscle mass, fat mass, and body fat percentage). Linear regression models examined associations between training type (direct-contact vs. non-contact sports) and follow-up body fat percentage, BMI, and waist circumference as dependent variables, adjusting for covariates.

The study included 110 adolescents (39 female, 71 male) with median age 13.21 years (IQR: 12.46-14.33). Participants comprised 65 direct-contact and 45 non-contact athletes. Baseline prevalence rates were 27.27% for overweight/obesity, 24.55% for elevated waist circumference, and 16.36% for elevated blood pressure. At follow-up, corresponding rates were 24.55%, 26.36%, and 13.64% respectively. The elevated blood pressure subgroup showed significantly higher waist circumference (P=0.034), elevated waist circumference rate (P=0.011), and body composition weight (P=0.049) compared to normotensive peers. Longitudinal analysis revealed 56.36% of participants increased BMI and 63.64% increased waist circumference. Adjusted linear regression demonstrated significant inverse associations between direct-contact training and body fat percentage (β=-6.57, 95% CI: -9.37 to -3.78, P < 0.001), BMI(β=-1.30, 95% CI: -2.50 to -0.11, P=0.036), and waist circumference(β=-2.31, 95% CI: -4.40 to -0.22, P=0.034).

Despite regular athletic training, substantial proportions of adolescents exhibited overweight/obesity, abdominal obesity, and elevated blood pressure, warranting clinical attention. Training modality appears to influence body composition changes, with direct-contact sports associated with more favorable adiposity-related outcomes.

To investigate the mediating role of vitamin D in the association between exerciseand triglyceride among adolescents, as well as its potential molecular mechanisms.

This prospective cross-sectional study utilized convenience sampling, enrolling 2021-grade students from Jining No. 7 Middle School on June 5, 2023. Moderate-intensity exercise frequency was assessed via standardized questionnaires, serum 25-hydroxyvitamin D levels were measured using chemiluminescence, and triglyceride levels were determined via fully automated biochemical analysis. Spearman's rank correlation analysis was employed to examine the relationships among moderate-intensity exercise, triglyceride, and vitamin D. A mediation model was constructed using the Baron & Kenny causal steps approach, adjusting for confounders including age, sex, body mass index (BMI), dairy intake, sweet food consumption, and fast-food intake. Subgroup analyses were performed based on BMI. The significance of the mediation effect was confirmed using both the Bootstrap and Sobel tests.

A total of 354 adolescents meeting the inclusion criteria were enrolled, including 142 females (40.11%) and 212 males (59.89%), with a median age of 13.25(12.83, 13.83)years. Spearman's analysis revealed a significant negative correlation between moderate-intensity exercise and triglyceride levels (r=-0.21, P < 0.001), a significant negative correlation between vitamin D and triglyceride (r=-0.30, P < 0.001), and a significant positive correlation between moderate-intensity exercise and vitamin D levels (r=0.26, P < 0.001). The mediation model indicated that vitamin D partially mediated the triglyceride-lowering effect of exercise (52.22%, 95% CI: -0.027 to -0.009, P < 0.001), with the effect remaining significant after confounder adjustment (47.83%, 95% CI: -0.019 to -0.005). Subgroup analysis showed that in adolescents with BMI < 24 kg/m², vitamin D accounted for 82.01% of the mediation effect between exercise and triglyceride (95% CI: -0.022 to -0.005, P=0.005), which remained significant after adjustment (81.20%, 95% CI: -0.022 to -0.005, P=0.005). In contrast, among adolescents with BMI ≥24 kg/m², the mediation effect was nonsignificant before (3.38%, 95% CI: -0.014 to 0.009, P=0.760) and after adjustment (7.51%, 95% CI: -0.019 to 0.012, P=0.621).

Vitamin D serves as a key mediator in the triglyceride-lowering effect of exercise among adolescents, independent of age, sex, and dietary habits. This mediation effect is particularly pronounced in adolescents with BMI < 24 kg/m². The underlying mechanism may involve vitamin D-regulated lipid metabolism-related gene expression and suppression of inflammatory pathways, suggesting that targeting vitamin D signaling could be a potential molecular strategy for early intervention in adolescent dyslipidemia.