Intermuscular adipose tissue affected muscle density more than intramuscular adipose tissue content with opportunistic screening at abdominal CT

This study aimed to determine whether intermuscular adipose tissue (IMAT) or intramuscular adipose tissue content (IMAC) has a greater effect on skeletal muscle density (SMD) and to explore the underlying mechanisms. We recruited 292 inpatients without musculoskeletal system disease, all of whom underwent abdominal CT. Muscle parameters, including skeletal muscle area (SMA), skeletal muscle index (SMI), SMD, IMAC, and IMAT, as well as fat parameters-subcutaneous fat area (SFA) and subcutaneous fat density (SFD) in the abdominal wall-were measured by two musculoskeletal radiologists using ImageJ software at the third lumbar vertebra (L3) level. One-way ANOVA with LSD (chi-square test for group comparisons where p > 0.05) or Dunnett's T3 test (p < 0.05) was employed to compare muscle parameters between genders and across age groups. The relationship between SMD and muscle measurements was analyzed using Spearman's correlation coefficient. Multiple regression analysis identified and compared factors influencing SMD. SMD was highly correlated with IMAT and IMAC (p < 0.05), moderately correlated with gender, age, and SFA (p < 0.05). Multiple linear regression analysis indicated that IMAC, IMAT, and age significantly affected SMD (p < 0.05), with the order of influence being IMAT (beta = -0.616), IMAC (beta = -0.429), and age (beta = -0.098). SFA and gender did not significantly affect SMD (p > 0.05). The findings revealed that age, IMAT, and IMAC influence SMD, with IMAT exerting the most significant impact.