Body Composition - Fat - Weight

Body composition is the term used to describe the different components that, when taken together, make up a person's body weight. The human body is composed of a variety of different tissue types including lean tissues (muscle, bone, and organs) that are metabolically active, and fat (adipose) tissue that is not.

Body Weight Measurements

Standard body weight scales provide a measure of total weight, but don't determine the lean-to-fat ratio of that weight. Standing on most scales can tell you only if you weigh more than the average person, but not if that weight is fat or muscle. Based only on scale weight, a 250-pound athlete with 8% body fat may be considered "overweight" by a typical weight chart. Such charts are not a good indication of ideal body weight for general health or for athletic performance.

Body Composition | Body Fat Measurement

There are many methods of assessing a person's fat and lean mass. The most common methods include the following.

Underwater Weighing - Hydrostatic Weighing

One method of body composition analysis in which a person is weighed while submerged in a large tank of water is called underwater or hydrostatic weighing This method of determining body composition relies on Archimedes' Principle of displacement which states:

1. The density of fat mass and fat-free mass are constant
2. Lean tissue is more dense than water
3. Fat tissue is less dense than water.
4. Therefore person with more body fat will weigh less underwater and be more buoyant.

Underwater weighing has been considered the gold standard for body composition assessment, however new, more sophisticated methods may make underwater weighing obsolete in the future.

Skinfold Thickness Measurements

Because underwater weighting it is complicated and cumbersome and requires special equipment, most exercise physiologists use simple skinfold measurements to determine body fat percent. The American College of Sports Medicine says that when performed by a trained, skilled, tester, they are up to 98% accurate.

Bioelectrical Impedance

Bioelectrical Impedance is another method of assessing body fat percentage. There are a variety of body composition and body fat analyzers and scales available for home use that provide more than just total weight measurements. These devices determine total weight, the percent and amount of body fat, muscle mass, water, and even bone mass. While the readings can be affected by hydration levels, food intake, skin temperature, and other factors, if you follow the directions and take the reading under similar conditions, you will obtain the best results.