A More Comfortable Method For Hydrostatic Weighing: Head Above Water At Total Lung Capacity

Body composition is an important indicator of overall health, and hydrostatic weighing (HW) is one of the many methods of determining body composition. The gold standard of HW requires full submersion with the lungs at residual volume (RV) which is uncomfortable and unnatural. PURPOSE: Therefore, the purpose of this study was to find a more comfortable way to complete hydrostatic weighing. To accomplish this, three tests were done: 1) the concordance of HVPRED equations, 2) the validity of TLC using RV, and 3) the validity of HAW@TLC using HBW@RV. METHODS: A convenience sample of participants self-reported age, sex, gender, and physical activity level. Height, weight, head girth, and face girth were taken prior to HW. A HW system was used to complete three different techniques: head above water (HAW) at total lung capacity (TLC), head below water (HBW) at TLC, and HBW at RV. Three consistent trials of each technique within 100 g were used for analysis. RESULTS: Data of all 122 participants was separated by males (n = 64) and females (n = 58). Three comparisons were formed from the three techniques: Comparison 1 (HBW@TLC vs HAW@TLC), Comparison 2 (HBW@RV vs HBW@TLC), and Comparison 3 (HBW@RV vs HAW@TLC). Comparison 1: HAW@TLC resulted in higher mean percent body fat (PBF) than HBW@TLC (4.5% total, 3.8% in males, 5.4% in females, p < 0.05). Comparison 2: HBW@TLC resulted in lower mean PBF than HBW@RV (5.1% total, 5.3% in males, 4.8% in females, p < 0.05). Comparison 3: HAW@TLC resulted in lower (1.5% lower, p = 0.003) mean PBF for males but not females and the total (0.6% higher, p = 0.39, 0.6% lower, p = 0.18, respectively) compared to HBW@RV. Bland-Altman plots showed proportional bias in comparisons 2 and 3, both overall and for females, but not males. Lin’s Concordance Correlation Coefficient showed high concordance in Comparisons 1 and 3, but moderate concordance in comparison 2. CONCLUSION: In conclusion, HW is the gold standard method, but it can cause physical and psychological discomfort which deters participation. The results show that both head position and lung volume affect PBF results. Comparison 3 results suggest that HW can still be accurate and more comfortable, especially for people who dislike full submersion or cannot perform it, such as children and people with obesity and pulmonary disease.