THE EFFECTS OF VARIOUS LEVELS OF HYDRATION ON AIR DISPLACEMENT PLETHYSMOGRAPHY AND DUAL ENERGY X-RAY ABSORPTIOMETRY

Abstract

PURPOSE The purpose of this study was to examine the effects of hydration status on the estimation of body composition by Air Displacement Plethysmography (ADP) and Dual Energy X-ray Absorptiometry (DEXA). METHODS Twenty healthy normal-weight college age males (n=10) and females (n=10) were assessed for urine specific gravity (USG) via refractometer, and percent body fat (%BF) by ADP and DEXA at euhydration and following 1%, 2% and 3% dehydration induced by physical exercise in a climate control chamber. Assessments followed procedures delineated by manufacturer's specifications. Assessment of heart rate, skin temperature, and respiratory rate were made at euhydration and following each dehydration condition to insure subjects' return to baseline prior to ADP and DEXA. Mean differences among hydration conditions were assessed by a one between (Gender) by two within (Body Composition Methods, Hydration status) multiple factors repeated measures ANOVA. Post Hoc procedures with Bonferroni correction were employed to assess the significance of selected treatment comparisons. Significance levels for ANOVA and family-wise error rates were set at 0.05. RESULTS %BFADP, following 1%, 2% and 3% dehydration, for both males and females were significantly different from euhydration, while %BFDEXA did not significantly change across hydration conditions. %BFADP significantly underestimated %BFDEXA by 8.2% (females) and 11.3% (males) at euhydration and increased to 13.7% to 20.8% underestimation following dehydration for both genders. CONCLUSIONS Accepting DEXA as the reference standard, it is concluded that ADP underestimates %BF in both genders and this underestimation increases during periods of dehydration. This study demonstrates that hydration status should be controlled when assessing %BF by ADP.