Body Composition 411.

A scale does not decipher between body fat and lean body mass. Therefore it is most important to understand what your body composition is to make good judgments. Learn more here!

Individuals are usually most concerned with optimizing body composition. A scale accurately measures body weight, but a scale does not decipher between body fat and lean body mass (muscle, bone, organs, etc).

The body mass index (BMI) is a common tool used to classify various levels of obesity; the BMI, like a scale, does not decipher between adipose and lean tissue either, though.

What this means is after practicing all you've learned from, those firm, lean bodies may provide a "false" sense of overweight or obesity, when in reality your body is healthy and lean. Body composition is the only option, then, to separate your lean body mass from your fat mass.

It is obviously healthier to have more muscle than fat; this is not only true for health and wellness, but physical performance as well. Therefore, scientists have developed a variety of techniques to measure various body components.

Body Components

The body can essentially be broken up into four major components:

  1. Total Body Fat: Consists of both essential fat and storage fat. Essential fat is necessary for optimal functioning whereas storage fat is simply a place (or places) for excess energy.

  2. Fat-Free Mass: Consists primarily of protein and water. Skeletal muscles are the main component of fat-free mass, but organs such as the heart, kidneys, liver, etc. are also included.

  3. Bone Mineral: Bone is crucial for body structure and some metabolic processes. This can be accounted for through various body composition assessment techniques.

  4. Body Water: Average adult body weight is roughly 60 percent water. This too is accounted for in a variety of body composition techniques.

Body Analyzation

There are over a dozen different methods to analyze body composition. We will uncover some of the more popular ones that may be available at a fitness center near you.


Bioelectrical Impedance Analysis (BIA)

This technique uses the concept that lean tissue and water conduct electricity better than fat. A low-level electrical signal (that the person does not feel) is passed through the body. Based on the resistance to the signal, total body water is calculated and the value can be used to estimate percent body fat.

The signal can be conducted by standing on a scale where the signal is passed from one foot to the other and extrapolated to the upper body. Another method is to pass the signal from electrodes placed at the hand and foot. This second assessment method tends to be more accurate of the two. The accuracy of BIA ranges from 3 to 5%, and is dependent on a variety of factors.


  • Fast
  • Easy
  • Can be inexpensive (as low as $100)


  • Crucial to maintain normal hydration status (water conducts electricity), meaning you can not participate in vigorous exercise within 12-24 hours.
  • Refrain from eating within 4 hours of measure.

Skinfold Measurements

Skinfolds are an estimate of total body density made from a measure(s) of subcutaneous fat. There are a number of different measurement sites that can be used and there are a variety of formulas used with skin calipers.

There is some associated measurement error with skinfolds, so it is important to relay this information to the client; the value they obtain typically has a 3 to 5% error margin because it is an estimate, based on assumptions, and many factors are taken into account.

If someone is overfat, skinfold calipers will not be accurate because the average thickness of their subcutaneous tissue is too large for an accurate reading. If the same trainer is doing the measurements consistently and using the same formulas and sites to measure bodyfat, it will increase the reliability of the measurement.


  • Ease of use.
  • Low cost involved.
  • Minimal training necessary.


  • Limited population (if overfat, calipers will not be accurate).
  • Requires the same trainer to perform measurement to increase reliability.

Near Infrared Reactance (NIR)

This method of body composition analysis is based on the principles of light absorption and reflection. A fiber optic probe is placed in the middle of the biceps and it emits an infrared light beam, which painlessly penetrates fat and muscle, but reflects off of bone.


  • Convenience
  • Ease of use
  • Portability
  • Hydration status does not affect results


  • More expensive than many methods

Hydrostatic Densiometry

This is a common tool used in research laboratories. It was considered the "gold standard" of body composition assessment tools, although new techniques are being developed and researched continually. The typical UWW assumes the body is comprised of fat mass and fat free mass and the calculations are formulated from this assumption.


  • It is reliable.
  • It is valid.


  • It is time consuming.
  • Uncomfortable for many individuals to perform.
  • Requires special equipment, typically "housed" in a University or hospital.

Body Composition Summary

The current average percentages of body fat for U.S males is 15 to 18% and 22 to 25% in females. In the OC, body fat percentages average 3% for males and 10% for females (OK, OK, just kidding). A "good range" for athletic males and females is considered 11 to 14% for males and 16 to 23% for females.