Novel comparative analysis and equation development for body volume estimation using dual-energy x-ray absorptiometry in athletes.

Background/objectives: Dual-energy x-ray absorptiometry (DXA) has been suggested as an alternative method for estimating body volume (BV), a component of the reference four-compartment body composition model. This study reports the development and validation of DXA-BV_Silva, a novel DXA-derived BV equation. An additional aim was to develop an estimate of lean soft tissue density (D_LST), a key variable in the theory-based approach, by estimating total body protein with a six-compartment model.

Methods: A sample of 332 athletes (36.7% females) from several sports were randomly assigned to either the development (n = 232) or cross-validation group (n = 100). DXA-BV_Silva was developed via linear regression of DXA-measured fat, lean soft tissue, and bone mineral mass against BV measured with air displacement plethysmography (ADP). A D_LST estimate of 1.064 kg/L (SD = 0.006) was obtained from a subset of the development sample comprising 201 athletes (36.3% females) with available measurements of total-body water by deuterium dilution, bone mineral by DXA and BV by ADP, enabling total-body protein determination from a six-compartment model.

Results: DXA-BV_Silva provided the closest BV estimation (mean difference = 0.05 L, SD = 0.46 L; ES [95% CI] = 0.11 [-0.08; 0.31]) and the 95% limits of agreement (-0.86 to 0.96 L) were narrower than existing empirical equations.

Conclusion: We conducted the first comparative analysis of both empirical and theoretical BV estimation methods using DXA, demonstrating the validity of DXA-BV_Silva for BV estimation in athletes, presenting a robust alternative to ADP, with potential applications in multicomponent body composition models.