Rapid Four-Compartment Models in Athletes Using Alternative Solutions for Body Volume and Water

The criterion four-compartment (4C) model combines dual-energy x-ray absorptiometry (DXA), deuterium dilution, and air displacement plethysmography (ADP), but its complexity limits practicality. This study aimed to externally validate a DXA-derived body volume (BV) equation (DXA-BV_Silva) and assess the accuracy of a rapid 4C model replacing deuterium dilution total body water (TBW) with bioelectrical impedance spectroscopy (BIS) alongside DXA-derived BV in athletes. A total of 143 athletes (27.3% females) validated DXA-BV, with 115 (33.9% females) assessed for FM. Criterion 4C used DXA for bone mineral content, ADP for BV, and deuterium dilution for TBW. Several rapid 4C models were tested. DXA-BV_Silva and DXA-BV_Heymsfield reliably estimated BV, showing minimal mean differences and narrow 95% limits of agreement (LOA) compared to ADP. Among rapid 4C models, 4CTBW_BIS, 4C BV_SilvaTBW_BIS, and 4C BV_HeymsfieldTBW_BIS provided the most accurate FM estimates with small, nonsignificant differences to the criterion (MD [SD]: -0.18 [1.25] kg; -0.23 [1.82] kg; 0.18 [1.87] kg, respectively) and narrow 95% LOA (-2.62 to 2.27, -3.79 to 3.33 and - 3.48 to 3.83 kg, respectively) with no proportional bias. This research supports the implementation of rapid 4C models in settings where the criterion 4C model is impractical. By improving accuracy in body composition assessment, our findings have implications for sports nutrition, sports science, and academic research, offering a viable alternative to traditional 2C and 3C models (DXA).