X-rays of two different energies are used to scan the body, one of which is absorbed more strongly by fat than the other. Body fat may be estimated from the body mass index by formulae derived by Deurenberg and co-workers. For convenience, an instrument which must be stepped on will also measure weight. A computer can subtract one image from the other, and the difference indicates the amount of fat relative to other tissues at each point. This estimate is distorted by the fact that muscles and bones have different densities:
Older individuals are found to have a lower body density for the same skinfold measurements , which is assumed to signify a higher body fat percentage. Methods using circumference have little acceptance outside the Department of Defense due to their negative reputation in comparison to other methods. Navy circumference method compares abdomen or waist and hips measurements to neck measurement and height and other sites claim to estimate one's body fat percentage by a conversion from the body mass index. Although it may not give an accurate reading of real body fat percentage, it is a reliable measure of body composition change over a period of time, provided the test is carried out by the same person with the same technique. March Learn how and when to remove this template message The bioelectrical impedance analysis BIA method is a lower-cost from less than one to several hundred US dollars in  but less accurate way to estimate body fat percentage. Some formulas require as few as three measurements, others as many as seven. The method is safe, noninvasive, rapid and easy to use. For example, the U. There is little scope for technician error as such, but factors such as eating, drinking and exercising must be controlled  since hydration level is an important source of error in determining the flow of the electric current to estimate body fat. A computer can subtract one image from the other, and the difference indicates the amount of fat relative to other tissues at each point. One way to regard these methods is that they trade accuracy for convenience, since it is much more convenient to take a few body measurements than to submerge individuals in water. Marine Corps also rely on the height and circumference method. Whole-body air displacement plethysmography[ edit ] Body composition measurement with whole-body air displacement plethysmography ADP technology Whole-body air displacement plethysmography ADP is a recognised and scientifically validated densitometric method to measure human body fat percentage. X-rays of two different energies are used to scan the body, one of which is absorbed more strongly by fat than the other. The two methods may give different percentages, without being inconsistent, as they measure fat in different parts of the body. Body fat may be estimated from the body mass index by formulae derived by Deurenberg and co-workers. Some, referred to as multicompartment models, can include DXA measurement of bone, plus independent measures of body water using the dilution principle with isotopically labeled water and body volume either by water displacement or air plethysmography. Unsourced material may be challenged and removed. From this data, a formula relating the body measurements to density is developed. Ultrasound[ edit ] Ultrasound is used extensively to measure tissue structure and has proven to be an accurate technique to measure subcutaneous fat thickness. Air-displacement plethysmography offers several advantages over established reference methods, including a quick, comfortable, automated, noninvasive, and safe measurement process, and accommodation of various subject types e. Expansions[ edit ] There are several more complicated procedures that more accurately determine body fat percentage. However, older, highly athletic individuals might not fit this assumption, causing the formulas to underestimate their body density. Because most anthropometric formulas such as the Durnin-Womersley skinfold method,  the Jackson-Pollock skinfold method, and the US Navy circumference method, actually estimate body density, not body fat percentage, the body fat percentage is obtained by applying a second formula, such as the Siri or Brozek described in the above section on density. Instruments require details such as sex and age to be entered, and use formulae taking these into account; for example, men and women store fat differently around the abdomen and thigh region. These measurements are then looked up in published tables, with the individual's height as an additional parameter. The general principle behind BIA:
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