Sex-specific patterns of skeletal muscle aging at the L3 level: a quantitative study based on opportunistic CT

This opportunistic CT-based study aimed to investigate age- and sex-related changes in muscle mass and quality at the L3 vertebral level in men aged ≥ 50 years and postmenopausal women.

Clinical and abdominal CT data from 292 hospitalized patients (146 men, 146 women) were retrospectively analyzed. At the L3 level, skeletal muscle area (SMA), skeletal muscle index (SMI), skeletal muscle density (SMD), intermuscular adipose tissue (IMAT), and intramuscular adipose tissue content (IMAC) were measured using Image J. Two-way ANOVA was used to test for sex-by-age interactions. Univariate linear regression and LOESS smoothing were additionally applied to quantify and visualize age-related trajectories, respectively.

All CT-derived measurements showed excellent inter-rater reliability (ICC > 0.75). Two-way ANOVA revealed significant sex-by-age interactions for SMA and SMI (p = 0.001 and p = 0.003, respectively), but not for SMD or IMAT. Men exhibited a more rapid age-related decline in muscle mass: each additional year of age was associated with a decrease in SMA of 1.331 cm² in men versus 0.465 cm² in women. Women demonstrated an earlier onset of muscle quality deterioration. Compared with younger postmenopausal women, older postmenopausal women had significantly lower SMD (p < 0.05), and IMAT increased significantly after age 60 (p < 0.05). IMAT was a more sensitive imaging biomarker of age-related myosteatosis than IMAC.

Opportunistic CT-based assessment reveals a distinct sexual dimorphism in skeletal muscle aging: men lose muscle mass more rapidly, whereas women experience an earlier onset of muscle quality decline, driven predominantly by intermuscular fat infiltration. Opportunistic CT effectively captures these sex-specific differences, supporting its application in opportunistic screening and sex‑specific management of sarcopenia.