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

Objective This study utilized opportunistic abdominal CT data to investigate age- and sex-related changes in muscle mass and quality at the third lumbar vertebra (L3) level in males over 50 and postmenopausal females. Methods Clinical and imaging data from 292 hospitalized patients (146 males, 146 females) admitted between July 2019 and July 2022 were retrospectively analyzed. Patients with musculoskeletal or other wasting diseases were excluded. Skeletal muscle area (SMA), skeletal muscle index (SMI), skeletal muscle density (SMD), intramuscular adipose tissue content (IMAC), and intermuscular adipose tissue (IMAT) were measured at the L3 level using Image J software. Sex- and age-stratified analyses were performed to delineate differential aging patterns. Inter-rater reliability was assessed using the intra-class correlation coefficient (ICC). Independent sample t-tests and one-way ANOVA were used for group comparisons, and univariate linear regression to analyze the impact of age. Results Measurements for all muscle parameters demonstrated excellent inter-rater reliability (ICC > 0.75). In males, SMA, SMI, and SMD declined significantly after age 70 (p < 0.05), accompanied by a significant increase in IMAT (p < 0.05). In females, SMD decreased significantly across all postmenopausal age groups (p < 0.05), while IMAT increased markedly after age 60 (p < 0.05). Notably, while the decline in muscle mass was more pronounced in males, the deterioration of muscle quality and fat infiltration occurred earlier and were more severe in females. Regression analysis showed that with each additional year of age, SMA decreased by 0.504 standard units in males vs. 0.267 in females, whereas the decline in SMD was similar between sexes. Conclusions Our findings reveal a sex-dimorphic pattern of skeletal muscle aging: males experience a more rapid loss of muscle mass, while females exhibit an earlier and more pronounced decline in muscle quality, driven by accelerated intermuscular fat infiltration. These insights underscore the need for sex-specific strategies in the assessment and management of sarcopenia and related musculoskeletal aging.