Bio-Electrical Impedance Analysis
My interest in BIA took root very early in my life. This led me to conjoined research in engineering and medical streams. I reached a point where I just had to make this machine, as it could improve the quality of human life.
— Dr. Kichul Cha, CEO, InBody
Behind the Scenes
InBody devices use BIA to measure body composition dividing your weight into components such as lean body mass and fat mass to assess health and nutrition.
The Science
Bioelectrical Impedance Analysis measures impedance by applying alternating currents through the human body.
Concept 01
Imagine the flow of cars on a highway your car is the electrical current, and the road is body water. Without other cars, you'd move freely. But as more cars enter, resistance grows. Similarly, elements like fat, muscle, and bone resist electrical current in the body.
The more water (and thus muscle) in your body, the lower the resistance to electrical current.
Concept 02
Reactance also known as capacitive resistance is the opposition to the instantaneous flow of electric current caused by capacitance. It measures a cell's ability to store energy and provides an indirect measure of cellular strength and integrity.
Concept 03
Impedance is the vector sum of resistance and reactance. BIA applies a cylinder model to relate impedance to the human body, using two fundamental formulas calculating cylinder volume and the relationship between impedance and body water.
Because impedance is inversely proportional to cross-sectional area and directly proportional to length, we can calculate total body water simply by knowing impedance and height making accurate height measurement essential.
The History of BIA Technology
From Hoffer's foundational experiments to Dr. Cha's breakthrough trace the evolution that made InBody possible.
Hoffer proved that total body water and impedance are highly correlated, showing that height² ÷ impedance correlated 0.92 with total body water the foundational impedance index used in BIA today.
RJL Systems commercialized the first BIA device using a 50kHz current. BIA was fast, affordable, and non-intrusive compared to calipers or underwater weighing.
Lukaski and Kushner developed equations using age, gender, and weight. While useful for general populations, these estimations introduced bias for atypical body types.
Japanese manufacturers released consumer BIA scales measuring impedance hand-to-hand or foot-to-foot. Easy to use but limited in clinical precision.
Kushner argued the body is five cylinders each arm, each leg, and the torso. The torso alone accounts for ~50% of lean body mass yet was largely ignored by whole-body measurement.
Harvard's Dr. Kichul Cha invented the world's first 8-point tactile electrode system with direct segmental multi-frequency analysis measuring all five body segments independently, without empirical equations.
Four Pillars of InBody Technology
InBody's medical-grade analyzers rely on four core technologies to deliver results highly correlated to gold-standard methods.
01
Strategically placed electrodes control contact resistance, ensuring consistent and reproducible measurements every time.
02
Independent measurements for each of the body's 5 cylinders including the critical torso for unmatched accuracy.
03
Currents at varying frequencies provide the most precise body water analysis, distinguishing intracellular and extracellular water.
04
Your results are based solely on your body's actual impedance unaffected by age, ethnicity, or gender assumptions.
Technical Deep Dives
BIA Problem
Changing measurement position changes impedance, introducing error.
InBody Solution
8-Point Tactile Electrode System with Thumb Electrodes ensures fixed measurement points.
The thumb electrode ensures that voltage measurement always starts at the wrist — regardless of how the user holds the device. The anatomical design creates a simple, easily reproduced holding position with exceptionally high reproducibility.
The 8 contact points: two thumb electrodes, two palm electrodes, two sole electrodes, and two heel electrodes — measurement is always taken at the ankle level for the feet.
Traditional BIA treats the body as a single cylinder, ignoring the torso — which comprises ~50% of lean body mass. A 5-ohm change in torso impedance appears as less than 1% in whole-body measurement, causing massive underestimation.
InBody directly measures each of the five body segments — left arm, right arm, left leg, right leg, and torso — at multiple frequencies. Because each ohm of torso impedance represents a large amount of lean body mass, separate torso measurement is critical for clinical accuracy.
The impedance values for all five cylinders appear directly on your InBody Result Sheet, offering full transparency into your body composition data.
Traditional BIA Problem
Whole-body single-cylinder measurement ignores the torso — effectively overlooking half the body.
InBody DSM-BIA Solution
Five segments × multiple frequencies = the most accurate, granular body composition data available without invasive procedures.
Empirical equations use population averages — plugging your age, gender, and weight into a preset formula. Your result is predetermined, not measured. An elderly female bodybuilder will be calculated as having average elderly-female muscle mass, regardless of reality.
InBody measures impedance for each of the five body segments independently. Your height and those impedance values alone determine your body composition — no age, gender, or ethnicity variables involved. Your body is measured as yours.
Test any device: run the same person twice, switching the entered gender. If results differ, the device uses empirical estimations.
Sample Empirical Formula
TBW = 0.377 H²/R + 0.14 weight – 0.08 age + 2.9 gender + 4.65
InBody Formula
Body composition derived purely from impedance values × height — for each of the five segments.
Why InBody
Every InBody device is engineered around four non-negotiable principles that set it apart from any other BIA on the market.
98.4% correlation with DEXA the gold standard. Used in hospitals, sports medicine clinics, and research institutions worldwide.
Each limb and the torso measured independently giving you muscle imbalances, not just totals. The torso alone accounts for 50% of lean body mass.
Low and high frequency currents distinguish intracellular from extracellular water enabling phase angle, ECW/TBW ratio, and other advanced biomarkers.
Learn More
More from InBody India to help you understand and choose the right body composition solution.
10,000+ peer-reviewed studies on DSM-BIA across clinical specialties and diverse populations.
ReadWhat every metric means ECW/TBW ratio, phase angle, visceral fat level, segmental lean analysis.
ReadThe 4 components of body composition and why tracking them matters more than weight alone.
ReadHow InBody DSM-BIA compares to DEXA gold-standard: 98.4% correlation, 60-second scan, no radiation.
ReadExperience DSM-BIA
Direct Segmental Multi-frequency BIA is what powers every InBody scan. Find a verified test centre near you and experience your full body composition report in 60 seconds.
