ASSESSMENT OF THE COMPOSITION OF MAJOR BODY REGIONS BY DUAL-ENERGY X-RAY ABSORPTIOMETRY (DEXA), WITH SPECIAL REFERENCE TO LIMB MUSCLE MASS

Dual-energy X-ray absorptiometry (DEXA) has been used to assess and compare the composition of whole body and major body regions in 12 female (weight, 56.9 +/- 6.2 kg; BMI, 17-25 kg M-2 ) and 16 male (weight, 73.1 +/- 9.6 kg; BMI, 20-28 kg m-2 ) healthy subjects. Standard deviations (and % coefficients of variation) of the differences between repeated measurements of fat ranged from 0.11 kg (9.0%) for arms to 0.42 kg (3.0%) for whole body; for arm bone mineral, 0.01 kg (2.0%), and for fat-free soft tissue of the whole body, 0.42 kg (0.8%). Limb muscle mass was estimated using a new theoretical model of body composition, and the corresponding precision ranged from 0.15 kg (3.8%) to 0.27 kg (1.5%) for arms and total limb muscle mass, respectively. Proportions of each region consisting of fat were greater in females than in males (range, 20-31% vs. 16-18%), respectively, but the ratio of trunk to leg fat was lower (34:49% vs. 46:38%, respectively). Regional proportions of bone were similar between the sexes (all in the range 2.9-5.6%, for both females and males). Mean total limb muscle masses were 14.2 kg (arms, 2-8 kg; legs, 11-4 kg) for females and 22.2 kg (arms, 4.8 kg; legs, 17.4 kg) for males, which were 33.6% and 36.0% of fat-free mass, respectively. The correlation coefficients between limb muscle (DEXA) and other indices of muscle mass were: for DEXA vs. total body potassium, 0.90 (SEE 1.1 kg muscle mass) to 0-94 (1.6 kg); and for DEXA vs. anthropometry, 0-43 (1-2 kg) to 0.85 (1-3 kg). Those for limb volume (DEXA) vs. anthropometric volume, 0.91 (0.78 1) to 0.94 (1.91 1). It is concluded that DEXA enables the valid and reproducible estimation of fat, fat-free soft tissue, bone, and limb muscle mass.