Body Composition 411

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A scale may tell you how much you weigh, but it can't decipher between body fat and lean body mass (muscle, bone, organs, etc.) and that's the same with the old standby formula to determine your body mass index (BMI). Keep in mind that in general, though, with most individuals, having too much muscle isn't an issue; 65% of Americans are currently overweight or obese, so too much muscle would actually be a good thing!

However, though, what that means is, if you've been training hard and you want to know how much muscle you've gained and how much fat you've lost, you're going to need to do a proper body composition test. There are several different ways to do it. Here are some of the most basic ones.

Bioelectrical Impedance Analysis (BIA)
This technique, which uses a low-level electrical signal that passes through the body, is based on the concept that lean tissue and water conduct electricity better than fat. As the signal shoots through your body (you won't feel a thing), it calculates the amount of resistance to determine total body water. The value is then used to estimate your percentage of body fat.

The signal can be conducted by standing on a scale where the signal is passed through each foot and extrapolated to the upper body. Another method is to pass the signal from electrodes placed on the hands and feet. This second assessment method tends to be more accurate of the two. The accuracy of BIA ranges from 5 to 7 percent, according to a study published in the International Journal of Sports Medicine, and is dependent on a variety of factors such as hydration status, race, time and duration of last workout, among others.

Pros: It's fast, easy and can be inexpensive (as low as $100), if you buy a less expensive machine.
Cons: It's crucial to maintain normal hydration status (water conducts electricity), meaning you can't participate in vigorous exercise within 12-24 hours of taking the test. And, you have to refrain from eating 4 hours before the test. Some machines can cost up to $1,400.

Skinfold Measurements
Skinfolds are an estimate of total body density made from a measure (or measures) 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 overweight, 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 body fat, it will increase the reliability of the measurement.

Pros: It's easy to use, sometimes doesn't cost very much (as low as 14.99 and requires minimal training to operate-not no training, minimal training.
Cons: Doesn't work for everyone (if overweight, calipers will not be accurate). And it requires the same trainer to perform measurement to increase reliability. Some of the more reliable tools are upwards of $239.00.

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.

Pros: It's convenient, easy to use, portable, and your hydration status does not affect the results.
Cons: At around $4,000 per unit, it's more expensive than many methods.

Hydrostatic Densiometry (also known as underwater weighing-UWW)
This is a common tool used in research laboratories. It was considered the "gold standard" of body composition assessment tools, but new techniques, such as DEXA, 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. You can think of this method like one of those tanks at the fair, where you throw a ball at a circle and hope it knocks the person in the tank. It's obviously a bit more technical, but that's the general principle.

Pros: It is reliable and valid.
Cons: It is time consuming, uncomfortable for many individuals to undergo and requires special equipment, typically "housed" in a university or hospital.

Bod Pod
This is a relatively new and promising method to estimate body composition. It looks like a giant egg and is technically know as "Air Displacement Plethysmography." It is similar to UWW described above, but instead of displacing water by getting dunked in a tank, you displace air in this egg-like chamber.

Pros: Research has shown it's reliable and valid.
Cons: It requires special training and equipment. You would like only find these at Universities, hospitals, or select training facilities.

Body Composition Summary
The current average percentages of body fat for U.S. males is 15 percent to 18 percent and 22 percent to 25 percent for females. A "good range" for athletic individuals is 11 percent to 14 percent for males and 16 percent to 23 percent for females.