Total-body skeletal muscle mass: development and cross-validation of anthropometric prediction models

Background: Skeletal muscle (SM) is a large body compartment of biological importance, but it remains difficult to quantify SM with affordable and practical methods that can be applied in clinical and field settings. Objective: The objective of this study was to develop and cross-validate anthropometric SM mass prediction models in healthy adults. Design: SM mass, measured by using whole-body multislice magnetic resonance imaging, was set as the dependent variable in prediction models. Independent variables were organized into 2 separate formulas. One formula included mainly limb circumferences and skinfold thicknesses [model 1: height (in m) and skinfold-corrected upperarm, thigh, and calf girths (CAG, CTG, and CCG, respectively; in cm)]. The other formula included mainly body weight (in kg) and height (model 2). The models were developed and cross-validated in nonobese adults [body mass index (in kg/[m.sup.2]) [is less than] 30]. Results: Two SM (in kg) models for nonobese subjects (n = 244) were developed as follows: SM = Ht x (0.00744 x [CAG.sup.2] + 0.00088 x [CTG.sup.2] + 0.00441 x [CCG.sup.2]) + 2.4 x sex - 0.048 x age + race + 7.8, where [R.sup.2] = 0.91, P [is less than] 0.0001, and SEE = 2.2 kg; sex = 0 for female and 1 for male, race = -2.0 for Asian, 1.1 for African American, and 0 for white and Hispanic, and SM = 0.244 x BW + 7.80 x Ht + 6.6 x sex - 0.098 x age + race - 3.3, where [R.sup.2] = 0.86, P [is less than] 0.0001, and SEE = 2.8 kg; sex = 0 for female and 1 for male, race = - 1.2 for Asian, 1.4 for African American, and 0 for white and Hispanic. Conclusion: These 2 anthropometric prediction models, the first developed in vivo by using state-of-the-art body-composition methods, are likely to prove useful in clinical evaluations and field studies of SM mass in nonobese adults. Am J Clin Nutr 2000;72:796-803. KEY WORDS Limb circumference, skinfold thickness, body composition, skeletal muscle, nonobese adults