Comparing Dual X-Ray Absorptiometry to Anthropometry to Determine the Lean Mass-to-Bone Ratio

The muscle-to-bone ratio (MBR) is a body composition metric that examines the weight placed on the bone from muscle. Currently, two methods are used for calculating MBR: 1) dual X-ray absorptiometry (DXA), and 2) anthropometrics. This study compared these two methods of determining MBR. A total of 31 (n=16 male, n=15 female) had their body composition assessed via a whole-body DXA and anthropometrics, which consisted of 43 measurements (i.e., skinfolds, girths, lengths, and breaths). Anthropometric measures were analyzed using the five-way fractionation method. Anthropometric-derived muscle mass, residual mass, and skin mass were combined to obtain a comparable measure of DXA-derived lean mass (LM). The lean mass-to-bone ratio (LMBR) for DXA and anthropometrics was determined by dividing LM by bone mass (BM). Statistical significance was determined at an alpha value of p≤0.05. DXA- and anthropometric-derived LMBR (22.8±3.1 vs. 5.2±1.0) were significantly different. This difference was due to significant differences in both DXA- and anthropometric-derived measures of LM (56.7±13.0 vs. 42.6±11.7 kg), and BM (2.5±0.5 vs. 8.2±2.0 kg). Bland-Altman analysis revealed a negative bias between DXA- and anthropometrics-derived LMBR that increased with rising anthropometric-derived BM and LM. Therefore, the LMBR determined by DXA and anthropometrics cannot be used interchangeably.