Good read on BF testing methods besides the conventional ones (hydro and skinfold).
DEXA (Dual Energy X-ray Absorptiometry) - A relatively new technology that is very accurate and precise, DEXA is based on a three-compartment model that divides the body into total body mineral, fat-free soft (lean) mass, and fat tissue mass. This technique is based on the assumption that bone mineral content is directly proportional to the amount of photon energy absorbed by the bone being studied.
DEXA uses a whole body scanner that has two low dose x-rays at different sources that read bone and soft tissue mass simultaneously. The sources are mounted beneath a table with a detector overhead. The scanner passes across a person's reclining body with data collected at 0.5 cm intervals. A scan takes between 10-20 minutes. It is safe and noninvasive with little burden to the individual, although a person must lie still throughout the procedure.
DEXA is fast becoming the new "gold standard" because it provides a higher degree of precision in only one measurement and has the ability to show exactly where fat is distributed throughout the body. It is very reliable and its results extremely repeatable; in addition, the method is safe and presents little burden to the subject. Although this method is not as accurate in measuring the extremely obese and the cost of equipment is high, DEXA is quickly moving from the laboratory setting into clinical studies.
NIR (Near Infrared Interactance) - A fiber optic probe is connected to a digital analyzer that indirectly measures the tissue composition (fat and water) at various sites on the body. This method is based on studies that show optical densities are linearly related to subcutaneous and total body fat. The biceps is the most often used single site for estimating body fat using the NIR method. The NIR light penetrates the tissues and is reflected off the bone back to the detector. The NIR data is entered into a prediction equation with the person's height, weight, frame size, and level of activity to estimate the percent body fat.
This method has become popular outside of the laboratory because it is simple, fast, noninvasive, and the equipment is relatively inexpensive. However, the amount of pressure applied to the fiber optic probe during measurement may affect the values of optical densities, and skin color and hydration level may be potential sources of error. To date, studies conducted with this method have produced mixed results; a high degree of error has occurred with very lean and very obese people; and the validity of a single-site measurement at the biceps is questionable. Numerous sources report that more research is needed to substantiate the validity, accuracy and applicability of this method.
Magnetic Resonance Imaging (MRI) - An x-ray based method in which a magnetic field "excites" water and fat molecules in the body, producing a measurable signal. A person lies within the magnet as a computer scans the body. High-quality images show the amount of fat and where it is distributed. MRI takes about 30 minutes and is very safe as it uses no ionizing radiation, but use is limited due to the high cost of equipment and analysis.
Total Body Electrical Conductivity (TOBEC) - This method is based on lean tissue being a better conductor of electricity than fat. A person lies in a cylinder that generates a very weak electromagnetic field. The strength of the field depends on the electrolytes found in the person's body water. In about 10 seconds, TOBEC makes 10 conductivity readings that estimate lean body mass. Although very accurate, its use is limited due to the high cost of the equipment.
Computed Tomography (CT) - CT produces cross-sectional scans of the body. An x-ray tube sends a beam of photons toward a detector. As the beam rotates around a person, data is collected, stored, and applied to complex algorithms to build images that determine body composition. CT is particularly useful in giving a ratio of intra-abdominal fat to extra-abdominal fat. It is noninvasive, but potential is limited by exposure to radiation and high equipment cost.
BOD POD (Air Displacement) - Based on the same principle as underwater weighing, the BOD POD used computerized sensors to measure how much air is displaced while a person sits for 20 seconds in a capsule. It uses a calculation to determine body density, then estimated body fat. The equipment is very expensive and limited in availability.
BIA (Bioelectrical Impedance) - The only method that is based on measuring something, not estimating anything, is Bio-Impedance measurement. Bio-Impedance is a means of measuring electrical signals as they pass through the fat, lean mass, and water in the body. Through laboratory research we know the actual impedance or conductivity of various tissues in the body, and we know that by measuring current between two electrodes and applying this information to complex proven scientific formulas accurate body composition can be determined. The fact that the measurement is based on a reading of lean mass and not an estimate of fat mass, lends to a much more comprehensive testing method and results.
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