About Bioelectrical Impedance Analysis (BIA)

What is BIA?

Bioelectrical impedance analysis is the study of the electrical properties of biological material and its change over time. This includes humans, animals, fish, plants, vegetables, fruits and anything living. Even human circulation and breathing can be quantified with a real-time BIA instrument that has enough sensitivity and a short sampling interval[1].

The most popular application for BIA is predicting human body composition as a total body measurement from hand to foot where resistance and reactance are evident from a biological circuit that conducts alternating current. The source electrodes introduce an alternating current (50 Khz) at the base of the toes and fingers. The detecting electrodes measure the voltage drop due to this circuit at the anatomical land marks of the ankle and wrist bones. This is a four electrode, or tetrapolar measurement, which is optimal to eliminate electrode and field distribution problems associated with two electrode measurements. The conducting media has a resistive and capacitive electrical path. These two values are independently measured and resolve the cellular and ionic components of the material. The cellular volume is measured as capacitive reactance and the resistive volume as ionic resistance, both of which are expressed in ohms. Modeling these two values as their series or parallel equivalent circuits is important when comparing them to criterion methods.

1. Nyboer, J.: Electrical Impedance Plethysmography. Second Edition. Charles C. Thomas, Springfield, IL, 1970.


The very first BIA, developed for the Mount McKinley project in 1981, measured electrical resistance and reactance at 50 Khz, and used rechargeable batteries. The basic specifications of today’s Bioelectrical Impedance Analyzers are fundamentally the same as those of the original project. Every instrument manufactured by RJL Systems incorporates passive isolation for safety, accuracy and repeatability. Some BIA-101 analyzers are still in use after more than 20 years.

About BIA:

BIA, or bioelectric impedance analysis, is a fast, accurate and safe way to measure six key body composition elements. Through the study of the electrical properties of the body and their changes over time, health professionals can easily measure clients’ overall health and quickly chart their progress. BIA analysis is quick, painless and completely non-invasive, using four electrodes placed on the body: no needles or bloodwork required.

BIA can be performed on any living thing: humans, animals and even plants. It can be used in clinical, educational or research settings. Body composition assessment provides healthcare professionals and their clients with a powerful, accurate window into disease and health.

RJL Systems is an ISO 13485 registered company.

Abstracts of Papers written about BIA