HYDROSTATIC WEIGHING WITH HEAD ABOVE WATER IN OBESE AFRICAN AMERICANS: A VALIDATION STUDY 1161

Abstract

Hydrostatic weighing with head above water (HWhaw) allows estimation of body density (Db) in individuals who are unwilling to perform full submersion. The purpose of this study was to determine the validity of HWhaw in obese African American utilizing Db formulas validated in a non-obese population (Donnelly et al., 1988). Twenty-seven subjects(47±1 yr, mean±SE), 22 females (45±1%fat) and 5 males(35±1%fat), performed HWhaw at total lung capacity, and hydrostatic weighing fully submerged (HW). HW was performed at partial lung capacity to minimize the subjects' anxiety of performing a maximal exhalation during full submersion. Residual volumes were determined by oxygen dilution. Vital capacity was measured by spirometry. Subjects performed 5 trials using each method. Paired t-tests indicated that HWhaw overestimated Db relative to HW in women (1.009±0.001 vs. 0.996±0.001 g/cc, p<0.01) and men (1.058±0.031 vs. 1.017±0.003 g/cc, p<0.05). When these data were translated to%fat via the Brozek et al. equation, HWhaw underestimated%fat by 6.2±0.4 and 3.3±0.8 units for women and men, respectively (p<0.01). Despite these differences, the correlation coefficient for Db between methods was significant for women(r=0.81, p<0.01), suggesting a sensitivity to inter-individual variation in Db. No correlation was observed for men, likely due to the small sample size. In conclusion, HWhaw equations developed in a non-obese population systematically overestimated Db in the obese. HWhaw however, is a promising method that will be quite useful if population-specific equations are developed.