Objective To evaluate the correlation between ultrasound ossification ratio(OR) and exercise intensity among adolescents.

Methods This cross-sectional study used stratified sampling to select adolescents aged 11-15 years from a sports school and some ordinary middle schools in Shandong Province in June 2023. The participants were divided into two groups: competitive sports group (high exercise intensity), and general sports group (moderate exercise intensity), based on their exercise intensity. Ultrasound images of long bones from nine body regions (including 3 upper limb bones and 6 lower limb bones) were collected for both groups. Two sonographers interpreted the images and calculated the ultrasound OR values (the ratio of ossification center length to epiphyseal length on the standard ultrasound section). The intraclass correlation coefficient (ICC) was used to assess the consistency of image interpretation between the observers. Differences in ultrasound OR values between the two groups were compared, and multivariate Logistic regression analysis was performed to assess the correlation between ultrasound OR values and exercise intensity.

Results A total of 252 adolescents who met the inclusion and exclusion criteria were included, with 154 in the competitive sports group (97 males and 57 females) and 98 in the general sports group (52 males and 46 females). The median height and average daily exercise duration were significantly higher in the competitive sports group than in the general sports group (all P < 0.001). The overall ICC for the interpretation of ultrasound OR values of long bones at 9 sites in 50 adolescents by the two sonographers was 0.930 (range: 0.853-0.964), indicating excellent inter-observer consistency. The medial femoral ultrasound OR values were higher in the competitive sports group than in the general sports group for both males and females (males: 0.87±0.07 vs. 0.84±0.04, P=0.025; females: 0.90±0.06 vs.0.85±0.14, P=0.027). Additionally, the differences in ultrasound OR values between the groups were observed in the lateral femoral and fibular bones in males and the radial bone in females (all P < 0.05). Multivariate Logistic regression analysis showed that the reciprocal of the medial femoral ultrasound OR value was correlated with exercise intensity (OR=0.046, 95% CI: 0.012-0.145, P=0.043), indicating that a decrease of 0.1 in the reciprocal of the medial femoral ultrasound OR value (equivalent to an increase of approximately 0.05-0.10 in the ultrasound OR value) was associated with a 2.17-fold increase in the likelihood of high-intensity exercise.

Conclusions The medial femoral ultrasound OR value was correlated with exercise intensity among adolescents. This indicator may serve as an objective imaging parameter for assessing whether adolescent exercise meets recommended standards.