What Is Body Composition and How Is It Measured?
Definition of Body Composition
In physical fitness, body composition is defined as the percentage of fat, muscle, and bone in the body. Usually its expressed as a ratio of lean mass to fatty mass. Lean mass includes muscle, bone, skin, internal organs and body water. Fatty mass is mostly composed of body fat (subcutaneous fat) as well as internal essential fat surrounding organs. Body composition will typically be displayed as either a percentage of fat (body fat percentage or %fat) or as a percentage of lean body mass (LBM).
Why Is Body Composition Important?
Body composition is a much more accurate representation of a persons leanness than scale weight or Body Mass Index (BMI), because it does not rely on height and weight alone to measure leanness. It measures the ratio of body fat to lean tissue and bone in the body, not scale weight.
This is important, because a person may have a high-scale weight (even for their height), yet have also have a high muscle-to-fat ratio which makes them extremely lean. That same person might be labeled overweight using the standard BMI calculation, which does not take into account body composition, only mass (weight) relative to your height, weight, age and gender.
Excess body fat, or a body composition with a high fat-to-muscle ratio is unfavorable because it increases the risk of cardiovascular disease, Type II diabetes, Metabolic Syndrome and certain cancers. Excess body fat, especially at levels considered obese, can also put stress on the joints and interfere with mobility and the ability to perform everyday activities.
Body Composition and Physical Performance
For athletes or even weekend warriors who participate in competitive or recreational sports excess body fat can impair physical performance. In general, the less body fat, the better the performance. Body fat contributes no strength advantage to a person (unlike muscle), and can interfere with endurance, speed and agility.
From a purely aesthetics perspective, two people can have the exact same height and weight, yet look completely different due to variations in their body composition. Since fat takes up more space on the body, a person who has a high body fat percentage but the same height and weight as a person with a low body fat percentage and more lean muscle will look larger and less lean. This is why its important to use body composition, and not scale weight, to determine overall physical fitness and leanness.
Measuring Body Composition
There are a number of techniques and devices for testing and measuring body composition, including:
- Body fat calipers (hand-held, manual or electronic) which measures subcutaneous fat using a single or multiple skin fold tests
- Bioelectrical Impedance Analysis (BIA), which measures body composition by passing a weak electrical current through the body. The most common BIA devices are electronic body fat scales, although there are also hand-held versions.
- Hydrostatic Weighing,which involves submerging the body in a tank of water and measuring the buoyancy of the body (more muscle mass causes the body to sink, while more body fat causes it to rise.)
- Air Displacement Plethysmography (ADP) which uses the same principle as hydrostatic weighing, but instead measures the displacement of air in a sealed chamber, verses water.
- Dual X-ray Absorptiometry (DXA) uses a low-level X-ray to give very precise measurements of bone mineral content (BMC), bone mineral density (BMD), lean tissue mass, fat tissue mass, and % of fat.
- Magnetic Resonance Imaging or Computed Tomography, which like DXA, provides very detailed and accurate body composition measures.
The most common, inexpensive and accessible forms of body composition testing for most people continue to be calipers and bioelectrical impedance analysis.
Of the two, calipers are considered to be the most accurate typically within four percentage points of a persons actual body fat percentage which is usually sufficient for most people. The difference in accuracy between single-point skin fold caliper tests and multiple-point tests is marginal, and research has shown that a single-point test, when properly done, can be almost as accurate as hydrostatic weighing.
Calculating Body Composition
Body composition is calculated by taking a persons body fat percentage, and subtracting it from a persons total scale weight.
For instance, a 200 lb man with 10% body fat would have 180 lbs of lean mass, and 20 lbs of body fat, or 90% lean mass. Unlike BMI, height, age and gender are not a factor in calculating body composition, although age and gender do come into play when determining ideal body composition targets.
Recommended Body Composition
The National Institutes of Health (NIH) recommends that healthy adult men should have between 13-17 percent body fat, while adult women should have between 20-21 percent body fat. Men who have a body fat percentage that exceeds 25% and women who have more than 30% body fat are considered obese.
However, athletes or people participating in competitive sporting activities may benefit from even lower body fat levels than recommended by the NIH.
Theideal body composition may also vary depending on the type of sport or activity.
For example, the typical body fat percentage for a male basketball player is 9% (13% for women), while the average Olympic cross-country skier has 5% (11% for women) body fat. This has to do with the type of activity and motion involved in cross-country skiing, where less body fat-to-greater lean tissue is advantageous to the competitor because it maximizes power, while reducing drag.
Most female fitness models will have body fat percentages in the mid-to-low teens, while competitive female bodybuilders or figure competitors will have body fat levels in the high single-digits. Male bodybuilders when preparing for a show will often have body fat levels in the low single digits. However, in both female and male bodybuilding, these low body fat percentages are typically not sustained year-round, and are usually only attained in the weeks leading up to a competition.
Can You Have Too Little Body Fat?
While having a body composition that favors more muscle and less fat is generally a good thing, it is possible to have too little body fat. The body needs a certain amount of essential body fat to cushion organs, regulate temperature, and regulate certain essential body nutrients as well as produce hormones.
For men the amount of essential body fat is around 3 percent, for women its considerably higher, about 12 percent. While it is possible for people to drop below those minimum levels for short periods of time, consistently maintaining body fat percentages below these essential body fat levels can have serious long-term health effects. For example, in women, maintaining very low body fat levels (sub 13%) can intefere with normal menstruation and cause hair-loss, skin disorders and organ damage in both genders.