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Evaluating & Measuring Fitness

How is body fat calculated?

A Answers (4)

  • AJay Morgan, NASM Elite Trainer, Fitness, answered

    There are many different ways to calculate body fat. Three common tests that are administered by a professional trainer are:

    Bioelectrical Impedance: For this test, a low electric current is sent throughthe body. Muscle contains a lot of water, and water is a good conductor for electricity, so the current will sail through muscle until it gets to fat, which is not a good conductor. The machine takes this information to calculate your body fat percentage.

    Skinfold Measurements: This test is the only one that depends on a human. A professional will use a set of calipers to take measurements from certain sites on your body. Some tests require three sites, while others can require seven sites. Typical sites for measurements are usually thighs, stomach, and arms. The person administering the test will take a fold of skin and fat and measure with calipers. These measurements get plugged into a formula, which computes your body fat percentage.

    Hydrostatic Weighing: Of the three tests, this one is the most accurate. A person sits in a tub of water on a scale and submerges their entire body. All of the air in the lungs is blown out to give the most accurate reading. This test takes your underwater weight, and from that number your body fat percentage is calculated.

    There are also popular at home weight scales for individuals to do on their own, but I would advise having a professional administer one of the above techniques.

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  • AJoan Roth , NASM Elite Trainer, Fitness, answered
    There are several way to calculate body fat.  The most common methods include skin-fold calipers (measures fat based on the size of skins folds), bioelectrical impedance (sends an electrical current through the body to measure fat) and underwater or hydrostatic weighing (the proportion of fat to lean tissue is determined by weighing the person on land and then under water and figuring the difference).  It is best to be measured by a qualified fitness professional who has experience with one or more particular techniques.  If using the caliper method, you may also want to have the same person measure you each time as variation in the results can occur if someone positions a caliper in even a slightly different location.
  • There are seveal methods for calculating body fat.  Skin fold calipers are the most common. Also you have hydorstatic weighing which is the most accurate.  Bioelectrical impedance which is either a hand held device or scale.  If you belong to a gym it would be great to see a qualified fitness professional to measure it for you.  Otherwise most people buy scales that measure body fat.  These are not as accurate but it will help track your progress if you can't see any fitness professionals.
  • Body fat is calculated through several methods such as hydrostatic weighing, bioelectrical impedance, and skin fold calipers.

    Hydrostatic weighing requires a specialized location with access to a pool designed for this type of measurement. An individual is submerged into the pool and weighed; they are then the weighed on dry land. Since lean body mass is more dense, it will sink and the fat will float. The difference in the dry and wet weight is calculated to determine the amount of body fat the individual has. This is the most accurate form of measuring body fat.

    Bioelectrical impedance works by sending a low voltage electrical current through the body to measure fat. Since muscles are composed of a high percentage of water (which is a conductor of electricity) the current will pass through at a higher rate. This yields the percentage of body fat. Due to the electrical current, the accuracy of this method can be affected by levels of hydration.

    The skin fold method is a very common method of calculating body fat. This test estimates the percentage of body fat by using a caliper to measure the skin fold thickness at specific points on the body. The Durnin-Womersley formula is commonly used to calculate body fat. This formula uses four specific spots on the body for the calculation. These spots are the front of the upper arm (biceps), back of the upper arm (triceps), below the shoulder blade (subscapular), and just above the hipbone (iliac crest). The results of each measurement are added together and the sum is found on a Durnin-Womersley body fat percentage calculation table under the appropriate category and recorded. Although there is some error associated with this method, finding a skilled professional to perform it increases the accuracy.

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