PURPOSE: The purpose of the study was to derive prediction equations for head volume (HV) from head girths and diameters and to use the equations for hydrostatic weighing (HW).
METHODS: HW was performed with and without head submersion of subjects using a computerized, 4 load cell weighing system. Forty-four males and 46 females comprised the experimental groups from which equations were derived to predict HV by water displacement. HW was then performed on 46 additional subjects (21 males and 25 females) to compare body density (BD) and body fat percent (BF%) for head below water (HBW) and head above water (HAW) immersion using the HV prediction equations. Subjects exhaled to residual volume and maintained the same lung volume during the HAW phase and the HBW phase of each immersion trial.
RESULTS: Head girths showed higher correlations and smaller SEEs than head diameters for the prediction of HV. Regression analysis indicated that the equations with the highest R² and the lowest SEE were from head girth (HG), face girth (FG) and body mass in air (MA). The equation for males was HV = 0.1294·HG + 0.0299·FG + 0.0055·MA - 5.7506 (R² = 0.57, SEE = 0.26 L). The equation for females was HV = 0.1314·HG + 0.0504·FG + 0.0094·MA - 8.9008 (R² = 0.73, SEE = 0.21 L). The validation groups showed no significant differences (p < 0.05) in BD between HAW immersion and HBW immersion for either males (R² = 0.98, SEE = 0.0028 g·ml^-1) or females (R² = 0.90, SEE = 0.0054 g·ml^-1). There were no significant differences (p < 0.05) in BF% between HAW immersion and HBW immersion for either males (R² = 0.98, SEE = 1.16%) or females (R² = 0.90, SEE = 2.24%). Fluctuations in weight scale readings were significantly lower (p < 0.05) for HAW immersion than for HBW immersion in both males (SD_HAW= 0.31 kg, SD_HBW=0.40 kg) and females (SD_HAW=0.22 kg, SD_HBW=0.30 kg).
CONCLUSIONS: Weight readings are more stable and BD and BF% are not significantly different when HW is performed without head submersion using predicted HV.