Validity of mid-arm muscular area measured by anthropometry in nonobese patients with increased muscle atrophy and variation of subcutaneous fat thickness

Background: The anthropometric measurement of mid-arm muscular area (MAMA) involves overestimation because of various assumptions, this overestimation being progressive with increasing adiposity. However, the effects of muscle atrophy and variation of the subcutaneous fat thickness have remained uncertain. Objectives: The validity of MAMA estimated by anthropometry was examined by comparing with MAMA measured by computed tomography (CT) in a nonobese population. The effects of muscle atrophy and variation of the subcutaneous fat thickness on the validity of MAMA were examined by new indices. Subjects/Methods: The relative MAMA was compared between the anthropometric and CT methods in 45 patients. New indices were introduced for assessing muscle deformity (muscle deformity index, MDI) and subcutaneous fat variation (SFVI). The effects of MDI, SFVI and age on the difference of MAMA between the anthropometric and CT methods were investigated. Results: MDIs were positively correlated with age in males (r = 0.47, P < 0.05) and females (r = 0.66, P < 0.001). SFVI was positively correlated with age only in females (r = 0.54, P < 0.01). Even in these patients, the relative MAMA estimated by anthropometry was significantly associated with that measured by CT (r = 0.85, P < 0.0001 in males and r = 0.90, P < 0.0001 in females). A Bland-Altman plot indicated that the difference between both methods was relatively small, although increased adiposity might be a source of overestimation for anthropometric MAMA measurement. Conclusions: MAMA estimated by anthropometry was a reliable indicator of muscle mass in patients with muscle atrophy and varying thickness of subcutaneous fat in lean patients. European Journal of Clinical Nutrition (2010) 64, 899-904; doi: 10.1038/ejcn.2010.87; published online 26 May 2010