Near Infrared Interactance

Near-infrared interactance (NIR), although originally designed by the agriculture industry to asses the composition of grains and seeds, is used today by nutritionists and exercise scientists alike to provide estimates of %BF in patients and/or athletes [52]. This field technique operates on the principles of light absorption and reflection. By comparing the light absorption of two different wavelengths in combination with anthropometric data (weight and height), and the use of appropriate regression equations, %BF is estimated.

Some of the main advantages of this device are its speed, ease of use, high degree of portability and low cost. The test is performed in a matter of minutes (approximately 3 min) by placing an infrared probe over the biceps muscle and measuring optical densities of the underlying tissue. To standardize testing, two specific wavelengths based on the absorption of fat and water are used, and the instrument is calibrated by measuring a signal from a reference block made of Teflon [53]. Additionally, specific equations catered to individual patient populations can be used to help reduce variance [54].

Despite the appeal of this method, controversy exists regarding its validity. While some studies have claimed good reliability and validity in young athletes, others have shown poor correlation in specific patient populations, such as the obese [49]. The reviewed research consistently shows that NIR underestimates %BF, and this error is accentuated with increasing body fatness [55].

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