[Analysis of the prevalence of multimorbidity among adolescents aged 13-18 in Inner Mongolia Autonomous Region from 2019 to 2022 and its association with moderate to high-intensity physical activity].

<b>Objective:</b> To analyze the changes in the prevalence characteristics of multimorbidity among adolescents aged 13-18 in Inner Mongolia Autonomous Region from 2019 to 2022 and to explore the association between multimorbidity and moderate to high-intensity physical activity among them. <b>Methods:</b> A stratified random cluster sampling method was used to select students aged 13-18 in Inner Mongolia Autonomous Region every September from 2019 to 2022. Physical examinations, demographic characteristics, and depression-related surveys were conducted to analyze the multimorbidity of overweight, obesity, high blood pressure, myopia, spinal curvature abnormality, and depression. A logistic regression model was used to analyze the association between multimorbidity and moderate to high-intensity physical activity. <b>Results:</b> From 2019 to 2022, 70 972, 62 923, 80 254, and 78 288 study subjects were included, with the rates of multimorbidity being 56.4%, 55.4%, 57.2%, and 55.8%, respectively. The rates of multimorbidity remained relatively stable from 2019 to 2022 (<i>χ</i>²=0.06, <i>P</i>=0.950). The incidence of multimorbidity among girls was significantly higher than that among boys (<i>P</i><0.001). The incidence of multimorbidity among urban students was significantly higher than that among suburban students (<i>P</i><0.001). The incidence of multimorbidity among high school students was higher than that among middle school students (<i>P</i><0.001). The top three multimorbidity combinations were myopia and overweight/obesity (26.4%), myopia and high blood pressure (24.4%), and myopia and depression (19.8%), while the least common combination was depression and spinal curvature abnormality (1.1%). The multimorbidity patterns showed no significant differences between years (<i>χ</i>²=0.03, <i>P</i>=0.999). The multimorbidity status was significantly associated with the status of meeting the standard of moderate to high-intensity physical activity (<i>OR</i>=0.83, 95%<i>CI</i>: 0.80-0.86). The association was stronger in boys (<i>OR</i>=0.77, 95%<i>CI</i>: 0.73-0.81) compared with girls (<i>OR</i>=0.90, 95%<i>CI</i>: 0.85-0.96), with a significant interaction term (<i>P</i><0.001). <b>Conclusion:</b> From 2019 to 2022, the incidence of multimorbidity among adolescents aged 13 to 18 in Inner Mongolia Autonomous Region is relatively high, mainly due to the co-occurrence of myopia and other health problems. Adequate physical activity is an important factor in reducing multimorbidity.