Sex differences in the muscle volume of the iliopsoas in the elderly

The purpose of this study was to investigate sex differences in the muscle volume (MV) of the iliopsoas, psoas major, and iliacus muscles, normalized by fat free mass (FFM), in the elderly. The subjects were 15 males and 15 females 65 years of age or over. Serial transverse 1.5T magnetic images (10 mm slice) of each subject were taken between the 12^th thoracic vertebrae and the lesser trochanter. FFM was measured with a bioelectrical impedance analyzer. The mean MV of each muscle on the right and left sides were calculated and used for regression analysis of the relationship between MV and FFM. A significant correlation was observed between MV and FFM of the iliacus in both sexes (p<0.01), but not between the MV and FFM of the psoas major. MV normalized by FFM and cross-sectional area (CSA) normalized by FFM^2/3 showed significantly greater values for the psoas major in the males than in the females (p<0.001), but there was no sex difference in the MV or CSA normalized by FFM of the iliacus. These results suggest that elderly males tend to have a greater muscle volume and crosssectional area of the iliopsoas than elderly females, and that these sex differences are attributable to differences in the psoas major.