Hydrostatic weighing accuracy:
Comparison of methods
Underwater Weighing |
Body Mass Index (BMI) |
| If you lose 5 lbs of fat and gain 5 lbs of muscle, then your body will weigh more underwater. Fat floats in water but muscle sinks. |
If you lose 5 lbs of fat and gain 5 lbs of muscle, your BMI does not change. BMI can’t tell fat weight from muscle weight. |
Underwater Weighing |
Skin Folds |
| Results are valid for lean or fat subjects. Different testers consistently get the same result. Calculates actual body density from body volume. |
Only possible on lean subjects with loose skin. Different testers seldom get the same result. Body density is estimated by prediction equations. |
Underwater Weighing |
Body Impedance Analyzer (BIA) |
| Body water content has little effect on results. Different equipment => Similar results. Fat % estimated directly from calculated density. |
Strongly affected by body water content. Different equipment => Different results. Fat % is not directly related to BIA measurement. |
Underwater Weighing |
Air Displacement Plethysmography |
| Simple to calibrate in seconds with known weights. Air temperature does not affect the results. No gaskets to leak. |
Calibration with test volume is time consuming. Air temperature change in chamber => Error. Leaky gasket => Large error. |
Underwater Weighing |
Dual Emission X-Ray Absorptiometry (DEXA) |
| Low cost for equipment acquisition. Subjects are not exposed to X-Ray radiation. Testers do not need a special certification or license. Measures both subcutaneous & internal body fat. |
High cost for equipment acquisition. Subjects are exposed to X-Ray radiation. Specialized training and certification required. Does not measure internal body fat. |