Body composition

 

Body composition

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This article is about fat, bone, water and muscle content of the human body. For the body's chemical composition, see Composition of the human body. For the general composition of all organisms, see Biological organisation.

In physical fitness, body composition is used to describe the percentages of fat, bone, water and muscle in human bodies. Because muscular tissue takes up less space in our body than fat tissue, our body composition, as well as our weight, determines leanness. Two people of equal height and body weight may look completely different from each other because they have a different body composition.

Measuring body composition[edit]

Body composition (particularly body fat percentage) can be measured in several ways. The most common method is by using gun calipers to measure the thickness of subcutaneous fat in multiple places on the body. This includes the abdominal area, the subscapular region, arms, buttocks and thighs. These measurements are then used to estimate total body fat with a margin of error of approximately four percentage k points.

Another method is bioelectrical impedance analysis (BIA), which uses the resistance of electrical flow through the body to estimate body fat.

Assessment of somatic (skeletal) protein is typically determined by simple measurements and calculations including mid arm circumference (MAC), mid arm muscle circumference (MAMC), and creatinine height ratio (CHI). Creatinine height ratio is calculated as 24 hour urine creatinine multiplied by 100 over the expected 24 hour urine creatinine for height. This calculation results in a percentage which can indicate protein depletion.

Body composition measurement withWhole-Body Air Displacement Plethysmography (ADP) technology

Body composition measurement with Dual energy X-ray absorptiometry (DEXA) is used increasingly for a variety of clinical and research applications. DEXA Scan is a medical grade test and considered the Gold Standard in body composition testing over 99% accurate. Total body or estimated total body scans using DEXA give accurate and precise measurements of BMD and body composition, including bone mineral content (BMC), bone mineral density (BMD), lean tissue mass, fat tissue mass, and fractional contribution of fat.^[1]

A technique for measuring body composition has been developed using the same principles as under water weighing. The technique uses air, as opposed to water and is known as Whole-Body Air Displacement Plethysmography (ADP). Subjects enter a sealed chamber that measures their body volume through the displacement of air in the chamber. Body volume is combined with body weight(mass) in order to determine body density. The technique then estimates the percentage of body fat and lean body mass (LBM) through known equations (for the density of fat and fat free mass).

These measurements are extremely reproducible, making them excellent for monitoring pharmaceutical therapy, nutritional or exercise intervention, sports training and or other body composition altering programs. They are also fast, simple, non-invasive, and expose the subject to a level of x-rays less than that of a cross-country flight. DEXA exams provide both total body and up to 14 regional (trunk, individual arms & legs, android, gynoid, etc.) results.

Body Composition is also estimated using cross-sectional imaging methods like magnetic resonance imaging (MRI) and computed tomography(CT). Since MRI and CT give the most precise body composition measures to-date, many pharmaceutical companies are very interested in this new procedure to estimate body composition measures before and after drug therapy especially in drugs that might change body composition.

Ultrasound has also been used to measure subcutaneous fat thickness, and by using multiple points a measurement of body composition can be made. Ultrasound has the advantage of being able to also directly measure muscle thickness and quantify intramuscular fat.

Body Composition can also be measured using the skinfold test, this is done using a tool called a caliper. You can do this in nine steps,

1. Take measurements on the right side of the body.
2. Mark client up.
3. Pinch skin (KM) above mark
4. Pull fat away from muscles
5. Place caliper halfway between top and bottom of mark
6. Allow caliper to settle (1–2 seconds)
7. Take reading — repeat 15 seconds
8. Add up total (4) — average
9. Calculate body fat %

See also[edit]

• Body volume index
• Body mass index

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Typical body fat amounts[edit]

There is no single ideal percentage of body fat for everyone. Levels of body fat are epidemiologically dependent on sex and age.^[2] Different authorities have developed different recommendations for ideal body fat percentages. The table below from the American Council on Exercise (not an official government agency) shows how average percentages differ according to the specified groups and categories:^[1]

Description	Women	Men
Essential fat	10–13%	2–5%
Athletes	14–20%	6–13%
Fitness	21–24%	14–17%
Average	25–31%	18–24%
Obese	32%+	25%+

Essential fat is the level below which physical and physiological health would be negatively affected. Controversy exists as to whether a particular body fat percentage is better for one's health; athletic performance may also be affected. The leanest athletes typically compete at levels of about 6–13% for men or 14–20% for women. Bodybuilders may compete at ranges even lower than these levels. Certified personal trainers will suggest to male bodybuilders that they aim for a body fat percentage between 2% and 4% by contest time. However it is unclear that such levels are ever actually attained since (a) the means to measure such levels are, as noted below, lacking in principle, are inaccurate, and (b) 4–6% is generally considered a physiological minimum for human males.^[3]===