Bioelectric impedance analysis: A seemingly simple method for determining the lean body mass. Abbreviated BIA. There are two methods of the BIA. One involves standing on a special scale with footpads. A harmless amount of electrical current is sent through the body, and then the percentage of body fat is calculated. The other type of BIA involves electrodes usually placed on a wrist and an ankle and on the back of the right hand and on the top of the foot. The change in voltage between electrodes is measured. The person's body fat percentage is then calculated from the results of the BIA.