Body Composition Scale – Measurement Techniques Part 3 (Bioelectrical Impedance Analysis)

This is the third article in our series on body composition scales and measurement techniques. In Part 1 we introduced the concept of body composition measurement and early methods of estimating body fat percentages relative to total body weight. In part 2 we explored pre DXA average body density measurement. In this article, we will explore bioelectrical impedance analysis, commonly referred to as BIA.

Bioelectrical impedance scales for body composition analysis

The Bioelectrical impedance analysis (BIA) method is a more affordable but less accurate way to estimate body fat percentage. The general principle behind BIA: two conductors are attached to a person’s body and a small electrical current is sent through the body. The resistance between the conductors will provide a measure of body fat, since the resistance to electricity varies between adipose, muscular and skeletal tissue.

Fat-free mass (muscles) is a good conductor as it contains a large amount of water (approximately 73%) and electrolytes, while fat is anhydrous and a poor conductor of electrical current. Factors that affect the accuracy and precision of this method include instrumentation, subject factors, technician skill, and the prediction equation formulated to estimate the Fat Free Mass.

Criticiams Of Bio-electrical Impedance Analysis Body Composition Scale Measurement Methodology

Criticism of this methodology is based on where the conductors are placed on the body; typically they are placed on the feet, with the current sent up one leg, across the abdomen and down the other leg. As technician error is minor, factors such as eating, drinking and exercising must be controlled since hydration level is an important source of error in determining the flow of the electrical current to estimate body fat.

As men and women store fat differently around the abdomen and thigh region, the results can be less accurate as a measure of total body fat percentage.

Variables Affecting Accuracy of BIA Body Composition Scale Readings

Another variable that can affect the amount of body fat this test measures is the amount of liquid an individual has consumed before the test. As electricity travels more easily through water, a person who has consumed a large amount of water before the test will measure as a lower body fat percentage. Less water will increase the percentage of body fat.

Also reducing the reliability of this method is the variation between models of the BIA devices: for instance when comparing outputs from a Tanita scale to an Omron Body Logic handheld device the Tanita scale overestimated the percentage body fat in college-aged men by 40% and in college aged women by 55%.

Availability of BIA Body Composition Measuring Devices

Bioelectrical impedance analysis is available in a laboratory, or for home use in the form of body fat scales and hand held body fat analyzers.