Distribution of subcutaneous fat and muscle thicknesses in young and middle-aged women.

Thicknesses of subcutaneous fat tissue at 13 sites (triceps, biceps, forearm, subscapular, abdomen, suprailiac, axilla, chest, quadriceps, suprapatellar, hamstrings, posterior calf, medial calf), and muscle tissue at nine sites (triceps, biceps, forearm, subscapular, abdomen, quadriceps, suprapatellar, hamstrings, posterior calf) were determined by using the B-mode ultrasound technique. Subjects were 36 young (18-29 years) and 44 middle-aged women (45-64 years). Body density averaged 1.047 ± 0.007 g · ml-1 (SD) for the young, and 1.022 ± 0.005 g · ml-1 for the middle-aged women. The middle-aged women showed significantly thicker subcutaneous fat than the young at all sites, and the relative differences between the two groups were larger on the trunk and adjacent sites. Muscle thicknesses on the trunk and quadriceps were significantly higher in the young women than in the middle-aged, but values for the upper extremities and calf were not significant between the two groups. The sum of subcutaneous fat thicknesses at 13 sites was significantly correlated with fat mass relative to the second power of stature (FM · St-2 ) in both groups, r = 0.766 (P < 0.05) for the young and r = 0.803 (P < 0.05) for the middle aged women. For subcutaneous fat thickness per unit FM · St-2 , the young women showed significantly higher values than the middle-aged on both the upper and lower extremities. The sum of muscle thicknesses at nine sites was significantly correlated with fat-free mass per unit stature2 (FFM · St-2 ) in both groups, r = 0.764 (P < 0.05) for the young and r = 0.636 (P < 0.05) for the middle-aged. The relative values of muscle thicknesses to FFM · St-2 were significantly lower on the abdomen and quadriceps in the middle-aged women than in the young. Thus compared with the young, the middle-aged women have thicker subcutaneous fat thicknesses along the whole body and thinner muscle thicknesses on the trunk and quadriceps regions. Moreover, it appears that in middle-aged women, the relative distribution of subcutaneous fat and muscle thicknesses to FM and FFM, respectively, show disproportionately higher fat stores internally than subcutaneously, and more rapid atrophy of muscle tissues at the anterior sites of the trunk and thigh than at other body sites. Am. J. Hum. Biol. 9:247-255, 1997. © 1997 Wiley-Liss, Inc.