Predicting composition of leg sections with anthropometry and bioelectrical impedance analysis, using magnetic resonance imaging as reference

Magnetic resonance imaging (MRI) was used to evaluate and compare with anth ropometry a fundamental bioelectrical impedance analysis (BIA) method for p redicting muscle and adipose tissue composition in the lower limb. Healthy volunteers (eight men and eight women), aged 41 to 62 years, with mean (S.D .) body mass indices of 28.6 (5.4) kg/m(2) and 25.1 (5.4) kg/m(2) respectiv ely, were subjected to MRI leg scans, from which 20-cm sections of thigh an d IO-cm sections of lower leg (calf) were analysed for muscle and adipose t issue content, using specifically developed software. Muscle and adipose ti ssue were also predicted from anthropometric measurements of circumferences and skinfold thicknesses, and by use of fundamental BIA equations involvin g section impedance at 50 kHz and tissue-specific resistivities. Anthropome tric assessments of circumferences, cross-sectional areas and volumes for t otal constituent tissues matched closely MRI estimates. Muscle volume was s ubstantially overestimated (bias: thigh, -40%; calf, -18%) and adipose tiss ue underestimated (bias: thigh, 43%; calf, 8%) by anthropometry, in contras t to generally better predictions by the fundamental BIA approach for muscl e (bias:thigh, -12%; calf, 5%) and adipose tissue (bias:thigh, 17%; calf, - 28%). However, both methods demonstrated considerable individual variabilit y (95% limits of agreement 20-77%). In general, there was similar reproduci bility for anthropometric and fundamental BIA methods in the thigh (inter-o bserver residual coefficient of variation for muscle 3.5% versus 3.8%), but the latter was better in the calf (inter-observer residual coefficient of variation for muscle 8.2% versus 4.5%). This study suggests that the fundam ental BIA method has advantages over anthropometry for measuring lower limb tissue composition in healthy individuals.