Near Infrared Interactance (NIR or simply Infrared for short) uses the principle of light absorption and reflection to measure body composition. The measurement is taken by placing a fiber optic wand on the belly of the biceps muscle. The wand sends a beam of infrared light into the muscle where shifts in the reflections of the wavelengths are used to estimate total body fat percentage.
The Futrex machine is the most common of the Infrared devices. Data on height, weight, age, sex, frame size, and activity level are entered into the Futrex machine and the machine prints out the results. The advantages of this method are that it's fast, simple, and noninvasive. The disadvantages include the high cost of the machine (a couple grand), and the questionable accuracy and reliability.
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