Abstract
Background: The rising prevalence of childhood overweight/obesity (OWOB) and elevated blood pressure (EBP) parallels a global decline in muscular fitness. However, evidence linking whole-body muscular strength to the comorbidity of these cardiometabolic risks remains scarce. Methods: Data were obtained from five nationally representative waves of the Chinese National Survey on Students' Constitution and Health (CNSSCH, 2000-2019), including 1,072,404 children and adolescents aged 7-18 years. A novel Muscle Strength Index (MSI) was developed by integrating handgrip strength (HGS) and standing broad jump (SBJ), standardized for body weight and height, respectively. Generalized linear mixed-effects models (GLMMs) with restricted cubic splines (RCS) were first applied to characterize dose-response associations. Subsequently, categorical analyses and forest plots were conducted to quantify risks of OWOB, EBP, and their comorbidity across five waves and subgroups. Sex-specific normative reference curves were established using the LMS method, and population-attributable fractions (PAFs) were estimated to assess the potential public health benefits of improving muscular strength. Results: Between 2000 and 2019, the prevalence of OWOB, EBP, and comorbidity increased markedly, reaching 25.80%, 12.23%, and 4.83% in 2019, and are projected to rise further to 37.88%, 20.16%, and 10.01% by 2030. Over the same period, mean MSI increased from 2000, peaked in 2005, and subsequently declined by 2019 with the values for boys and girls, being 1.73, 1.75, 1.63 and 1.46, 1.49, 1.41, respectively. Dose-response analyses revealed consistent L-shaped associations, with the greatest risk reductions observed when moving from low to moderate MSI levels. In 2019, participants with low MSI had higher odds of OWOB (OR 4.81, 95% CI 4.65-4.97), EBP (OR 1.42, 95% CI 1.36-1.49), and comorbidity (OR 3.49 95% CI 3.26-3.73) compared with those at middle levels. PAF analyses indicated that improving MSI to at least the 40th percentile could potentially avert 43.5% of OWOB cases, 12.3% of EBP cases, and 48.2% of comorbidity cases. The highest potential benefits were observed in northern and northeastern provinces, particularly Tianjin and Heilongjiang. Conclusions: Chinese children and adolescents face a dual burden of rising cardiometabolic comorbidity and declining muscular strength. Muscular strength demonstrates a strong nonlinear protective association with OWOB, EBP, and their co-occurrence. Targeted improvement among those with low muscular strength may substantially reduce future cardiometabolic burden.