What is Bio-Electrical Impedance Analysis (BIA)?

InBody devices use a method called Bio-electrical Impedance Analysis (BIA) to measure body composition, which divides your weight into different components such as lean body mass and fat mass to assess health and nutrition.Bioelectrical Impedance Analysis (BIA) measures impedance by applying alternating currents on the human body.


The Concept of Resistance

To better illustrate how this works, imagine the flow of cars in traffic. Your car is the voltage source or current, and the highway you’re on is body water. If there were no other cars, you could zoom past the highway, just as if the human body were full of body water and nothing else, there would be no resistance.

But water is not the only element in the human body, just like you’re not the only car on the freeway.  As more cars get onto the freeway, the longer it takes for you to get through the path, creating resistance. Other elements such as fat, muscle, bone, and minerals create resistance to the electrical current that is going through your body.

In BIA, the more water that is in your body, the lesser the resistance. The muscle in your body contains water, unlike fat, so the more muscle you have, the more body water. And the more body water you have, the lesser the resistance on the electrical current.



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8-Point Tactile

Electrode System


Direct Segmental Measurements


No Empirical



Multiple Frequencies


Other BIA Devices

The ability to distinguish between extracellular and total body water is critical to identify fluid imbalances related to acute inflammation or edema. Many BIA devices use only one frequency at 50 kHz to measure impedance, which does not fully pass through the body’s cells and makes the accurate measurement of total body water impossible. As a result, patients with increased extracellular water may have overlooked health risks.

InBody Devices

InBody uses a combination of low and high frequencies to accurately determine extracellular, intracellular, and total body water. The use of multiple frequencies allows InBody devices to achieve a high level of precision. Medical practitioners can use InBody for measurements of body composition and fluid status.

8-Point Tactile Electrode System

Other BIA Devices

Many BIA devices lack a thumb electrode or have hand electrodes positioned close together. These designs can cause measurements to start in the palm, which has a high impedance and can cause inaccuracies or lead to inconsistent measurement starting points, reducing the reliability of results.

InBody Devices

The anatomical design of the InBody hand electrode creates a simple holding position that is easy to reproduce. When an examinee grasps the handle, current flows from the palm electrode, and the electrical energy, or voltage, is initiated at the thumb electrode. The point of measurement remains consistent for highly reproducible results.


Direct Segmental Measurements

Other BIA Devices

Traditional BIA views the human body as one cylinder. However, the short length and large cross-sectional area of the torso mean that even a minor measurement mistake can lead to substantial error. For the most accurate results, BIA devices should measure the torso separately.

InBody Devices

Direct segmental measurement bioelectrical impedance analysis regards the human body as five cylinders: left arm, right arm, torso, left leg, and right leg. InBody independently measures each cylinder to provide accurate measurements for the entire body.


No Empirical Estimations

Other BIA Devices

Many BIA devices use empirical equations to compensate for technological flaws, including the lack of torso impedance (due to whole-body impedance measurement), single frequency measurements (which are unable to differentiate between water compartments), and lack of reproducibility (from electrode placement or positioning). These empirical equations utilize data, such as age, sex, and ethnicity, to calculate body composition based on common trends rather than relying solely on the individual’s actual body composition.

InBody Devices

InBody measures body composition without relying on empirical assumptions based on age, sex, ethnicity, or body shape, producing accurate and precise results validated to gold standard methods. Simply put, InBody provides individualized feedback for progress tracking to help you achieve your goals.