The body composition or  fat percentage is the relative amount of bodyfat. Although the fat percentage is more difficult to assess than for exmaple the BMI, it does give a more information about someone’s bodycomposition and wheter this person has a healthy weight or is over- or underweight.

Classification Men Women
Dangerously low <5% <12%
Athlete 5-7% 12-14%
Excellent 7-10% 14-18%
Good 10-16% 18-22%
Acceptable 16-19% 22-26%
Borderline 19-24% 26-31%
Overweight >24% >32%

When the fat percentage is used to determine whether someone has a healthy weight or not, there’s no risk of labeling someone with a large amount of muscle mass as overweight, while in reality this person has no increased risk on developing complications attributed to being overweight.

Body fat percentage can be estimated with the aid of a skinfold caliper or a bioelectric impedance scale. The skinfold caliper is used to assess the thickness of skinfolds on several locations of the body and adding these. The added value can then be looked up in a reference table which gives a corresponding fat percentage. There are several methods which use different skinfold locations and tables but one of the most used method is the method described by Durnin & Womersley and uses 4 skinfold sites. The advantage of this measurement is that it is cheap, valid and reliable if performed correctly.

A bioelectric impedance scale is widely used in fitness and health centers and personal trainers worldwide. It measures the electric resistance of the body with the aid of a small current and calculates a fat percentage based on this value. This method is easy to perform but it has its’ problems. There are large diferences in accuracy between different scales. In addition, this method is very sensitive for hydration, seeing as water conducts current more easily than fat, which affects reliability greatly.

There are more precise methods, but most of them are only available in hospitals or research centers, very expensive and/or unpractical and therefore of little use for most people. Examples of these are MRI-scan, BodPod or DEXA scan.

References:
-ACSM Guidelines for Exercise Testing and Prescription; 6th Ed., 2000.

-ACSM’s Resource Manual for Guidelines for Exercise Testing and Prescription, 4th Ed., 2001.

-Durnin J.V.G.A., Womersley, J. (1974). Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged 16-72 years. British Journal of Nutrition, 32, 77-97.