Advantages: Reasonably accurate; Quick and easy to do
Disadvantages: Subject to high variability; Inaccurate if individual has localized body fat
How it Works:
Calipers are used to measure the thickness of two layers of skin plus the subcutaneous (that right under the skin) fat at four to six locations around the body. The most common locations are triceps, shoulder blade, abdomen, calf and love handle area. These measurements are totaled to arrive at a sum of skinfolds which is put on a table which equates skinfold total to percent body fat.
Bio -- Impedance
Advantages: Quick and easy to do
Disadvantages: Readings are affected by hydration status and skin temperature; Inaccurate if individual has localized body fat
How it Works:
Subject either stands on a scale like device or holds an apparatus in outstretched hands and pushes a button. Button sends a very small current of electricity through that specific part of the body. Fat acts like the rubber insulation on a wire while muscle and bone and water all conduct electricity well. The larger the drop in current, the greater the body fat percentage.
*Special note: Since water and electrolytes both positively affect current flow, dehydration will cause body fat to be overestimated.
Be aware that since this machine only sends current through a specific part of the body, the accuracy of the readings are suspect. For example, most men do not store fat in their legs. If they are using a scale like device that send the electrical current through the legs, the overall body fat estimation will likely be low.
The following guidelines for recommended body fat levels for men and women are taken from the NHANES data gathered at the University of Arizona:
For females --
Basic health range: 14% to 38% fat
Optimal: 20% to 30%
Athletic performance: 17% to 25%
For males --
Basic health range: 5% to 25% fat
Optimal: 12% to 20%
Athletic performance: 8% to 15%
Remember that body mass index or BMI is not a body composition tool. BMI is a ratio of ones weight to height. Body mass index is not as precise for assessing ideal body weight as body composition testing is because it does not consider the ratio of fat to lean weight. The BMI scale penalizes people who have large bones and a larger amount of muscle mass. Using the BMI scale we would conclude every football player in the NFL is "overweight" or "obese" because their body weight to height ratio is very high. This of course is not true. Try to locate an exercise physiologist in your area who can measure your body composition and help you reach you optimum ratio of body fat to lean tissue.