• What is assessed?
• How is the measurement conducted?
• When is this method used?
• How are estimates of body composition derived?
• Strength and limitations
• Populations
• Further considerations
• Resources required
• Instrument library
• Development of new tool/method
• References

1. The near infrared interactance (NIR) method of assessing body composition is based on the principles of light absorption reflectance, and near infrared spectroscopy.
2. More specifically it is based on the ability of fat tissues to "absorb" more infrared light than lean tissue which can then be measured as a change in the infrared level.
3. The use of infrared (IR) light to measure fat was developed by the US Department of Agriculture to measure the fat contained in beef and pork carcasses after slaughter.
4. At approximately 928 nanometers, a direct measure of how much fat exists is provided by the absorption of the infrared portion of the spectrum.

A mono-chromator or light "wand" (see Figure 1), sends a low-energy beam of near-infrared light at about 900 nanometers into the biceps area that penetrates the underlying tissue to a depth of one centimetre. The energy is either 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.

This measure is rarely used for the assessment of body composition. Although it has good repeatability, it lacks validity in humans and its inability to accurately predict body fat across a broad range of fat levels is problematic. It assumes fat in the arm is proportional to total body fat, and research suggests that NIR may overestimate body fatness in lean people and underestimate it in people who are overweight.

The NIR data (density measurements) are entered into a prediction equation with the person's height, weight, age, gender, frame size, and level of physical activity. A digital read out including percentage body fat and lean tissue are displayed.

Figure 1 Example of Near Infrared Interactance.
Source: wikiHow.

An overview of the characteristics of near infrared interactance is outlined in Table 1.

Strengths

1. NIR measurement is safe and the equipment is portable and lightweight.
2. It requires little training to use.
3. The tool has a high level of repeatability.

Limitations

1. The amount of pressure applied to the fiber optic probe, skin color and hydration levels may cause results to differ and be inaccurate.
2. Some instruments have been shown to underestimated body fat by more than 4% in subjects greater than 30% fat and overestimated body fat by 4% in subjects less than 8% fat.
3. Poor validity.

Table 1 Characteristic of near infrared interactance.

Considerations relating to the use of NIR are summarised by population in Table 2.

There are no specific population for whom NIR cannot be implemented. It is easily administered and has shown a high level of repeatability. However, there is no research to support this method of body composition assessment in some populations and in the remainder, evidence highlights its poor accuracy and validity levels when compared to other more well established techniques such as hydrostatic weighing.

Table 2 Anthropometry by near infrared interactance in different populations.

*Based on poor validity.

The only known possible restriction on NIR is to avoid measurements on an extremely black tattooed location. The low energy NIR light might be totally absorbed by a very black tattoo.

Refer to section: practical considerations for objective anthropometry

1. NIR (Futrex) Body Composition Analyser
2. NIR (SCiO consumer physics) scanners with supporting devise requiring application with web interface

A method specific instrument library is being developed for this section. In the meantime, please refer to the overall instrument library page by clicking here to open in a new page.

The NIR (SCiO consumer physics) scanner is a new device. However, no validation work has been carried out to date to assess its use in the assessment of body composition.

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