Development of an anthropometric equation to estimate muscle mass in healthy Brazilian adults

Introduction: anthropometry is a practical and low-cost method for assessing body composition, capable of estimating body compartments. Skeletal muscle mass (SMM) is an important tissue for decision-making in clinical practice and for monitoring the health status of individuals. However, anthropometric equations that estimate SMM have limitations according to the specificities of the samples from which they were developed. Objective: the objective of this study was to develop a predictive anthropometric equation capable of estimating SMM in a sample of healthy Brazilian adults. Method: cross-sectional study using anthropometric and bioelectrical impedance analysis (BIA) data from 499 volunteers. To develop the equation, linear regression method was used, calculating adjusted R2 and standard error of estimate (SEE), in addition to the intraclass correlation coefficient (ICC) and the Bland-Altman test. Results: the final equation was: SMM (kg) = Height (cm) x (0.219 + 0.00001 x corrected thigh circumference2 [cm] + 0.00005 x corrected arm circumference2 [cm] + 0.00002 x corrected calf circumference2 [cm]) + 1.96 x Sex (Women = 0; Men = 1) + 0.079 x Weight (kg) - 26.98 (R2adj = 95.4 % and SEE = 1.522), which presented high agreement with SMM by BIA and the highest ICC, compared to other equations from literature (CCI = 0.988, 95 % CI [0.986-0.990]). The Bland-Altman analysis showed that the equation presented good agreement with the values obtained by BIA. Conclusion: the equation presented satisfactory diagnostic performance for estimating SMM in relation to BIA and uses parameters commonly collected in clinical practice.