Your body fat can be measured in a couple of ways. When you measure body fat you are trying to determine the amount of your body weight that is made up of fat (as opposed to other tissues such as muscle, bone, and body organs). The best methods are called laboratory measures and require experts who use expensive machines or equipment. DEXA is an X-ray technique that is considered the best way to measure body fat. It provides an X-ray picture that shows the bones and the fat and provides a measure of the percentage of the body tissue that is fat. Another very good laboratory measure is called underwater weighing. It uses the buoyancy of the body to calculate the percentage that is fat. For most people these are not practical because of the cost and time involved in having them done. Scientists have used these measures of body fat to create formulas that calculate estimates of body fat based on more practical methods.
More practical methods include skinfold measurements, body mass index, body measurements, and bioelectrical impedance. The following is an explanation of each of these.
Skinfold measurements use an inexpensive device called a skinfold caliper. The caliper is used to measure the thickness of folds of fat under the skin. A formula is then used to predict body fat from the skinfolds. To be accurate, the measurements must be made by a person who knows how to use the caliper and who has experience with testing. See page 95 in your text for more information.
Body mass index (BMI) estimates body fat based on the ratio of your height to your weight. To calculate your body mass index, first you measure your height and weight. Then you use a formula to calculate BMI using your height and weight. BMI does not determine body fatness, but it does give you a general indication about whether you are likely to be high in body fat. It has some limitations but is easy to measure. See pages 94 to 96 in your text for more information.
Body measurements of your waist size and hip size and other similar measurements can be used to estimate body fatness. You will learn more about these in high school. If you are interested in learning more, you can consult the high school version of the text Fitness for Life.
Bioelectrical impedance (BIA) machines have been shown to be accurate when used properly and when steps are taken to ensure that the machine is working properly. BIA uses a very, very low electrical current and measures how quickly it travels through your body. The current travels at different speeds in different types of body tissue. Calculations based on the speed of travel estimate the amount of body fat it traveled through. Like a scale for measuring weight, there may be some differences in measurement from machine to machine, so it is best to use the same machine each time you measure. Some schools and many doctors’ offices now have BIA for measuring body fatness.
For more information on body composition check Lesson 8.1 of the middle school textbook and Lesson 13.1 of the high school textbook.