Measurement Tools — Near Infrared Interactance


What It Is

NIR
NIR

Near infrared interactance (NIR) is based on a method developed by the United States Department of Agriculture to measure the body composition of livestock and the fat content of various grains. It uses the principles of light absorption and reflection to measure body fat. It is popular in some health clubs and weight loss centers and was

  • A light "wand" sends out a low-energy beam of near-infrared light into the biceps.
  • The energy is reflected, absorbed, or transmitted depending on the scattering and absorption properties of the biceps.
  • A detector within the wand measures the intensity of the re-emitted light.
  • Shifts in the wavelength of the reflected beam and a prediction equation are used to compute the percent body fat.

Equipment Used

Computerized spectrophotometer with a single, rapid scanning monochromator and fiber optic probe.

How It's Done

  • The probe sends out electromagnetic radiation from the monochromator to the surface of the biceps of a person's dominant arm.
  • The signal penetrates the underlying tissue to a depth of one centimeter.

Pros

  • The measurement is safe and the equipment is portable, and lightweight.
  • It requires little training to use.

Cons

  • This technique still lacks validation in humans.
  • It may not accurately predict body fat across a broad range of fat levels.
  • It may be less accurate than skinfold measures.
  • It assumes fat is the arm is proportional to total body fat. This may not be true.

Illustration courtesy Tanita Corporation of America Inc.

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