InBody Technology

Proving that Total Body Water is Highly Correlated with Impedance

In 1969, Hoffer et al. conducted a series of experiments to prove that total body water and impedance were highly correlated, suggesting that impedance measurements could be used for determining total body water.

The impedance of the right half of the body was measured and yielded promising results—the squared value of this length measurement divided by impedance highly correlated with total body water (r = 0.92).

RJL Systems and the First Impedance Meter

In 1979, RJL Systems made the first commercialized impedance meter that helped popularize the BIA method. The device measured impedance using a 50kHz current applied to the right half of the subject’s body via electrodes attached to the back of the right hand and on top of the right foot.

Previous body composition methods like calipers or underwater weighing were uncomfortable, required skilled technicians to install or operate, and could not test a wide variety of populations. Alternatively, BIA was easy, fast, less expensive, and non-invasive, making it popular with many researchers, nutritionists, and medical experts.

Development of Empirical Equations

In the 1980s, studies proved BIA had high correlations with standard methods, such as underwater weighing and DEXA; however, some technical limitations began to surface. Two limitations of BIA were its assumption of the human body as a single cylinder and its use of a single frequency (50 kHz). This method might work for users with standard body types, but it was inaccurate for certain populations. To improve accuracy, researchers derived various population-specific equations based on empirical data such as age, sex, and physical activity level for determining body composition.

While empirical estimations may be reliable for generally estimating an individual’s body composition, there are significant problems when they are used for medical purposes. These empirical estimations may deliver inaccurate results and oversimplify health risks in populations like obese young individual.

Consumer BIA Device

In the late 80s, Japanese manufacturers released several BIA devices for personal use, which gradually became more popular than professional medical models due to technological constraints mentioned earlier.

Some of these BIA devices were scales that measured the impedance between the user’s feet, while other models were handheld and measured the impedance between the user’s hands.
Both types of models potentially produced inaccurate results because they measured the arms or legs directly and estimated everything else.

Kushner and the Proposal of Multi-Frequencies With Segmental Analysis

In 1992, Dr. Robert Kushner proposed that the technical limitations of BIA could be improved by measuring the human body as five separate cylinders instead of one. Each cylinder has a different length and cross-sectional area resulting in varying impedance values.

With the single-cylinder model, the thinness and smaller cross-sectional area of the limbs reduce their impact on whole-body impedance. However, since the torso makes up 50% of fat-free mass, it is crucial to measure the torso separately for accurate results. Kushner emphasized that it is crucial to measure the torso separately for accurate results.

Dr. Cha Creates the InBody Professional Body Composition Analyzer

In 1996, Dr. Kichul Cha developed the world’s first 8-point tactile electrode system with direct segmental analysis to measure impedance in the five body cylinders using multiple frequencies (DSM-MFBIA technology).

Many BIA products provide segmental muscle and fat mass measures but not impedance, particularly in the torso.

The InBody device measured impedance in the limbs and torso separately, yielding highly accurate results without using empirical data based on age, sex, ethnicity, athleticism, and body shape. This innovative DSM-MFBIA technology makes the InBody a highly accurate and precise tool ideal for medical, fitness, and clinical applications.