<P> Intracellular fluid may then be estimated by subtracting extracellular fluid from total body water . </P> <P> Another method of determining total body water percentage (TBW%) is via Bioelectrical Impedance Analysis (BIA). In the traditional BIA method, a person lies on a cot and spot electrodes are placed on the hands and bare feet . Electrolyte gel is applied first, and then a weak current of frequency 50kHz is introduced . This AC waveform allows the creation of a current inside the body via the very capacitive skin without causing a DC flow or burns, and limited in the ~ 20mA range current for safety . </P> <P> BIA has emerged as a promising technique because of its simplicity, low cost, high reproducibility and noninvasiveness . BIA prediction equations can be either generalized or population - specific, allowing this method to be potentially very accurate . Selecting the appropriate equation is important to determining the quality of the results . </P> <P> For clinical purposes, scientists are developing a multi-frequency BIA method that may further improve the method's ability to predict a person's hydration level . New segmental BIA equipment that uses more electrodes may lead to more precise measurements of specific parts of the body . </P>

Which of these fluids constitutes the largest proportion of body fluids