3D Body Scanning-Derived Normative Values of Appendicular Circumferences: A Novel Tool for Sarcopenia Screening in Chinese Adults.

<p><b>BACKGROUND</b></p><p>Appendicular circumferences (ACs) are critical predictors of skeletal health, cardiovascular disease risk and mortality. Currently, comprehensive reference values and associated factors for thigh (TC), calf (CC), upper arm (UAC) and forearm (FC) circumferences remain unestablished in Chinese adults.</p><p><b>METHODS</b></p><p>This community-based cross-sectional study (China National Health Survey, April 2023-November 2024) enrolled 8915 adults (≥20 years) for reference value development and 10 632 for association analysis.

ACs were measured via 3D scanning, body composition via bioelectrical impedance analysis and handgrip strength using a Jamar dynamometer. Sex-specific centile curves (P2.5-P97.5) were generated using lambda-mu-sigma methods.

Propensity score matching balanced age distributions for sex and menopause subgroup comparisons. Multivariate logistic regression was used to examine factors associated with low appendicular circumference (lowest 5th percentile).</p><p><b>RESULTS</b></p><p>Median (25th and 75th) values for men were TC: 59.27 cm (55.09, 64.18), CC: 39.20 cm (37.17, 41.59), UAC: 28.31 cm (26.75, 30.10) and FC: 27.02 cm (25.67, 28.29); for women, TC: 52.45 cm (49.50, 55.74), CC: 35.71 cm (33.95, 37.76), UAC: 27.71 cm (25.74, 30.10) and FC: 24.64 cm (23.33, 26.07).

Age trajectories showed sex-specific patterns: TC, CC and UAC peaked at 20-29 years with subsequent decline, while FC peaked at 40-49 years. BMI-adjusted circumferences exhibited divergent aging trajectories by sex.

Postmenopausal women had significantly lower appendicular skeletal muscle mass (ASM), appendicular skeletal muscle mass index (ASMI), handgrip strength and CC than age-matched premenopausal women (all p values < 0.05). All ACs strongly correlated with muscle mass, fat mass and muscle strength (all p values < 0.001), with UAC and FC showing the strongest ASM and ASMI correlations in men (correlation coefficient: 0.757 and 0.735).

Factors associated with low ACs included rural residence, lower education, low BMI, elevated body fat (positively linked to low CC, especially ≥ 60 years) and cardiometabolic disorders (diabetes, hypertension, hyperuricemia, dyslipidemia).</p><p><b>CONCLUSIONS</b></p><p>This study establishes the first age- and sex-stratified percentile references for ACs in Chinese adults. These results reveal significant sex disparities in absolute and BMI-adjusted measures, providing essential tools for sarcopenia screening, lifestyle intervention evaluation and high-risk population identification.</p>