GLOSSARY

BIA Reference Table

BIA estimates compartments from impedance and a prediction model; the same reading can imply different composition under different assumptions.

Bioelectrical Impedance Analysis (BIA) uses electrical impedance measurements with prediction models to estimate body water and composition. The measured electrical signal should be distinguished from the modeled fat or lean output.

Bioelectrical impedance methods measure the body's opposition to an applied electrical current and use models to estimate water and body-composition compartments. Hydration, recent food, exercise, skin temperature and electrode placement can change the result. Extra frequencies or additional displayed compartments do not eliminate modeling assumptions. Compare measurements under standardized conditions on the same validated system. A consumer scale's apparent daily change in muscle or body-fat percentage should not be read as a direct tissue measurement.

Resistance reflects the resistive component of electrical opposition, while reactance reflects capacitive behavior. Impedance combines these components, and phase angle describes their relationship at a specified frequency. Interpretation depends on device and protocol as well as the individual. Phase angle is not a direct measure of muscle strength, hydration or a universal cellular-health score. Changes require context, and a single number cannot identify the exact nutritional problem or prove that a supplement has improved cell function.

Fat-free mass includes water, protein, minerals and other nonfat constituents. It therefore includes organs and bone as well as skeletal muscle. Lean body mass, fat-free mass and lean soft tissue can have different technical meanings, although terms are sometimes used loosely. A short-term rise in a device's lean-mass estimate can reflect hydration or glycogen rather than new contractile protein. Check the device definition and testing conditions before calling a change muscle growth.