Bioelectrical impedance analysis (BIA) has been reported to
be insensitive to changes in water volumes in individual subjects.
This study was designed to investigate the effect on the intra-
and extracellular resistances (Ri and Re) of the segments of
subjects for whom body water was changed without significant
change to the total amount of electrolyte in the respective
fluids. Twelve healthy adult subjects were recruited. Ri and
Re of the leg, trunk, and arm of the subjects were determined
from BIA measures prior to commencement of two separate studies
that involved intervention, resulting in a loss/gain of body
water effected either by a sauna followed by water intake (study
1) or by ingestion (study 2). Ri and Re of the segments were
also determined at a number of times following these interventions.
The mean change in body water, expressed as a percentage of
body weight, was 0.9% in study 1 and 1.25% in study 2. For each
study, the results for each subject were normalized for each
limb to the initial (prestudy) value and then the normalized
results for each segment were pooled for all subjects. ANOVA
of these pooled results failed to demonstrate any significant
differences between the normalized mean values of Ri or Re of
the segments measured through the course of each study. The
failure to detect a change in Ri or Re is explained in terms
of the basic theory of BIA.
