Standardized limb abduction for bioimpedance measurements using position restraints

Bioelectrical impedance analysis (BIA) measurements are widely used in the assessment of body hydration. However, there are many variables which can influence the impedance values obtained and their individual significance is not entirely clear. One such variable is limb position and it is possible to standardize this either by invoking subject cooperation or by the use of some form of mechanical constraint. This study evaluates these two approaches. BIA measurements were made on five healthy male volunteers both with the positioners and without. Additional variables including room temperature, prandial status, exercise, alcohol intake, bed surface for the test, and bladder status were controlled. The mean percentage difference between impedance values with and without positioners was (-0.37 +/- 0.69)%. The mean difference between occasions with and without mechanical fixing was (2.02 +/- 2.5)% and (2.58 +/- 3)% respectively. None of these differences is statistically significant. It was concluded that reproducibility of BIA measurements obtained with active subject cooperation in limb position is not significantly improved if mechanical positioners are used. This may not apply where subject cooperation is poor e.g. in very sick or very young people or in repeated measurements in different days.