Body fat percentage
The percentage of essential body fat for women is greater than that for men, due to the demands of childbearing and other hormonal functions.
A number of methods are available for determining body fat percentage, such as measurement with calipers or through the use of bioelectrical impedance analysis.
The widely used body mass index (BMI) provides a measure that allows the comparison of the adiposity of individuals of different heights and weights.
As such, BMI is a useful indicator of overall fitness for a large group of people, but a poor tool for determining the health of an individual.
This graph from the National Health and Nutrition Examination Survey (NHANES) in the United States charts the average body fat percentages of Americans from samples from 1999 to 2004: In males, mean percentage body fat ranged from 23% at age 16–19 years to 31% at age 60–79 years.
But it is important to recognise that women need at least 9% more body fat than men to live a normal healthy life.
[2] Data from the 2003–2006 NHANES survey showed that fewer than 10% of American adults had a "normal" body fat percentage (defined as 5–20% for men and 8–30% for women).
Certified personal trainers will suggest competitors keep that extremely low level of body fat only for the contest time.
[7] Irrespective of the location from which they are obtained, the fat cells in humans are composed almost entirely of pure triglycerides with an average density of about 0.9 kilograms per litre.
Most modern body composition laboratories today use the value of 1.1 kilograms per litre for the density of the "fat free mass".
Whole-body air displacement plethysmography (ADP) is a recognised and scientifically validated densitometric method to measure human body fat percentage.
Air-displacement plethysmography offers several advantages over established reference methods, including a quick, comfortable, automated, noninvasive, and safe measurement process, and accommodation of various subject types (e.g., children, obese, elderly, and disabled persons).
[13] Prior to the adoption of DXA, the most accurate method of estimating body fat percentage was to measure that person's average density (total mass divided by total volume) and apply a formula to convert that to body fat percentage.
Alternatively, an electrode may be held in each hand; calculation of fat percentage uses the weight, so that must be measured with scales and entered by the user.
Instruments require details such as sex and age to be entered, and use formulae taking these into account; for example, men and women store fat differently around the abdomen and thigh region.
Consequently, the body fat percentage calculated from skin folds or other anthropometric methods carries the cumulative error from the application of two separate statistical models.
The chief problem with all statistically derived formulas is that in order to be widely applicable, they must be based on a broad sample of individuals.
The accuracy of these estimates is more dependent on a person's unique body fat distribution than on the number of sites measured.
However, older, highly athletic individuals might not fit this assumption, causing the formulas to underestimate their body density.
[22] A-mode and B-mode ultrasound systems are now used and both rely on using tabulated values of tissue sound speed and automated signal analysis to determine fat thickness.
There is limited information, however, on the validity of the "rope and choke" method because of its universal acceptance as inaccurate and easily falsified.
When making calculations, the relationship between densitometrically determined body fat percentage (BF%) and BMI must take age and sex into account.
Internal and external cross-validation of the prediction formulas showed that they gave valid estimates of body fat in males and females at all ages.
[27] However – contrary to the aforementioned internal and external cross-validation –, these formulae definitely proved unusable at least for adults and are presented here illustratively only.
