Time Course Of Postural Fluid Shifts In A Sample Of Healthy Adults: Preliminary Data Findings

This study investigated the time required for ECW and ICW to stabilize in standing and supine positions. Forty-five healthy volunteers (36 + or - 16 yrs, 169.6 + or - 9.1 cm, 68.2 + or - 10.2 kg) followed standard pretest guidelines for body composition assessment. ECW and ICW were measured via MFBIA (Xitron Hydra 4200) every 5 minutes for 30 minutes per position. A 2-min seated period preceded assumption of each posture. FFM was calculated in accordance with the MFBIA analyzer manual (FFM = 1.106*ECW = 1.521*ICW). There were significant within-group main effects over time for supine ECW, ICW, TBW, FFM, and standing ECW (p < .05). There was no significant main effect for posture. Pairwise comparisons revealed significant differences between each 5-min increment (5 - 10, 10 - 15, 15 - 20, 20 - 25, 25 - 30 min) for supine ECW and ICW; supine FFM differed between 10 and 15 min (p < .01).