Regional skeletal muscle measurement: evaluation of new dual-energy X-ray absorptiometry model

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Abstract
Although there is growing interest in studying muscle distribution, regional skeletal muscle (SM) mass measurement methods remain limited. The aim of the present study was to develop a new dual-energy X-ray absorptiometry (DEXA) model for estimating regional adipose tissue-free skeletal muscle mass (AT-free SM). Relationships were derived from Reference Man data between tissue-system- level components (i.e., AT-free SM, AT, skeleton, and skin) and molecular-level components including fat-free soft tissue, fat, and bone mineral. The proposed DEXA-SM model was evaluated by multiscan computerized axial tomography (CT). Twenty-seven male subjects [age, 36 ± 12 (SD) yr; body mass, 73.2 ± 12.4 kg; 20 were healthy, and 7 had acquired immunodeficiency syndrome] completed DEXA and CT studies. Identical landmarks for DEXA and CT measurements were selected in three regions, including calves, thighs, and forearms. There was a strong correlation for AT-free SM estimates between the new DEXA and CT methods (e.g., sum of three regions, r= 0.86, P < 0.001). Regional AT-free SM measured in the 27 subjects by DEXA and CT, respectively, were 3.44 ± 0.60 and 3.47 ± 0.55 kg (difference 0.9%,P > 0.05) for calves, 10.49 ± 1.77 and 10.05 ± 1.79 kg (difference 4.4%,P < 0.05) for thighs, 1.36 ± 0.49 and 1.20 ± 0.41 kg (difference 13.3%,P < 0.01) for forearms, and 15.29 ± 2.33 and 14.72 ± 2.33 kg (difference 3.9%,P < 0.05) for the sum all three regions. Although the suggested DEXA-SM model needs minor refinements, this is a promising in vivo approach for measurement of regional SM, because DEXA is widely available, relatively inexpensive, and radiation exposure is low.