The body fat percentage ( BFP ) of humans or other living creatures is the total fat mass divided by total body mass, 100 times; Body fat includes essential body fat and body fat storage. Essential body fat is needed to sustain life and reproductive function. The percentage of body fat essential for women is greater than that for men, because of the demands of childbirth and other hormonal functions. The storage of body fat consists of fat accumulation in adipose tissue, which partially protects the internal organs in the chest and abdomen. The minimum recommended total body fat percentage exceeds the percentage value of the essential fat reported above. A number of methods are available to determine the percentage of body fat, such as measurement with calipers or through the use of bioelectric impedance analysis.
The percentage of body fat is a measure of fitness level, because it is the only body measurement that directly calculates the composition of a person's relative body regardless of height or weight. The widely used body mass index (BMI) provides a measure that allows for comparison of individual adiposity with different heights and weights. While BMI largely increases with increased adiposity, due to differences in body composition, other indicators of body fat provide more accurate results; for example, individuals with larger muscle mass or larger bones will have a higher BMI. Thus, BMI is a useful indicator for overall fitness for a large group of people, but a poor tool for determining one's health.
Video Body fat percentage
Common body fat amount
Epidemiologically, the percentage of body fat in individuals varies according to gender and age. Theoretical approaches exist in the relationship between body fat percentage, health, athletic capacity, etc. Different authorities have developed different recommendations for the ideal body fat percentage.
This graph of the National Health and Nutrition Examination Survey in the United States charts the percentage of average body fat of Americans from samples from 1999-2004:
In men, the average body fat percentage ranged from 22.9% at the age of 16-19 years to 30.9% at the age of 60-79 years. In women, the average body fat percentage ranges from 32.0% at 8-11 years old to 42.4% at the age of 60-79 years.
The table below of the American Council on Exercise shows how the average percentage varies according to the groups and categories specified:
Essential fat is the rate at which physical and physiological health will be negatively affected, and underneath definite death. Controversy exists, whether the percentage of certain body fat is better for one's health; Athletic performance may also be affected. Lean athletes usually compete at a rate of about 7-13% for men or 14-20% for women; Normal people, who do not have such huge muscle mass, should stay in the range of fitness on the table to be healthier. Bodybuilders can compete in various essential body fat, even certified personal trainers will advise them to keep the body fat level very low just for the time of the contest. It is not clear, however, that such levels have actually been achieved because (a) the means of measuring such levels, as mentioned below, are less than principally and inaccurately, and (b) 4-6% is generally regarded as the physiological minimum for men. man.
Maps Body fat percentage
Measurement techniques
Underwater weighing
Regardless of the location from which they were obtained, fat cells in humans are composed almost entirely of pure triglycerides with an average density of about 0.9 kilograms per liter. Most modern body composition laboratories currently use a value of 1.1 kilograms per liter for "fat free mass" density, a theoretical network of 72% water (density = 0.993), 21% protein (density = 1,340) and 7% mineral (density = 3,000) by weight.
With a well-designed weighing system, the body density can be determined with high accuracy by immersing a person in water and calculating the volume of water removed from the weight of the removed water. The correction is made for the buoyancy of air in the lungs and other gases in the body space. If there is no error whatsoever in measuring body density, the uncertainty of fat estimation will be approximately  ± 3.8% of body weight, mainly because of the normal variability in the body's constituents.
Pletimography whole-body air movement
Plethysmography of full body air movement (ADP) is a recognized and scientifically validated densitometry method for measuring the percentage of human body fat. ADP uses the same principle as the gold-standard method of weighing underwater, but represents a densitometric method based on air movement rather than on water immersion. Air-displacement plethysmography offers several advantages over existing reference methods, including a rapid, convenient, automated, non-invasive and safe measurement process, and accommodation of various types of subjects (eg children, obese people, parents, and people disabled). However, its accuracy decreases in the extreme percentage of body fat, tending to slightly shrink the percentage of body fat in overweight and obese people (by 1.68-2.94% depending on the method of calculation), and to exaggerate to a much more extent a large percentage of body fat on a very lean subject (with an average of 6.8%, with up to 13% exaggerated statements of reported body percentage of one individual - 2% body fat by DXA but 15% by ADP).
Near-infrared interactance
The infrared light rays are transmitted into the biceps. Light is reflected from the underlying muscle and absorbed by the fatileur. This method is safe, noninvasive, fast and easy to use.
X-ray energy absorber
Dual energy X-ray absorptiometry, or DXA (formerly DEXA), is a newer method for estimating body fat percentage, and determining body composition and bone mineral density.
X-rays from two different energies are used to scan the body, one of which is absorbed more strongly by fat than others. Computers can reduce one image from another, and the difference shows the amount of fat relative to other networks at each point. The total number of images allows the composition of the body as a whole.
Expansion
There are several more complicated procedures that more accurately determine the percentage of body fat. Some, referred to as multicomponent models, may include bone DXA measurements, plus independent measures of body water (using dilution principles with isotope-labeled water) and body volume (either by water movement or air plethysmography). Various other components can be measured independently, such as total body potassium.
Activation of in-vivo neutrons can measure all elements of the body and use mathematical relationships among elements measured in various components of the body (fat, water, protein, etc.) To develop a simultaneous equation to estimate the total body composition, including the body. fat.
Measurement of body-weight density
Prior to the adoption of DXA, the most accurate method for estimating body fat percentage was to measure the average density of the person (total mass divided by total volume) and apply a formula to convert it to body fat percentage.
Because fat tissue has a lower density than muscle and bone, it is possible to estimate the fat content. This estimate is distorted by the fact that muscles and bones have different densities: for someone with more than average bone mass, the estimate would be too low. However, this method gives highly reproducible results for individuals (Â ± 1%), unlike the methods discussed below, which can have uncertainties of 10%, or more. The percentage of body fat is usually calculated from one of two formulas (? Represents density in g/cm 3 ):
- Brozek formula: BF = (4.57/? - 4,142) ÃÆ'â € "100
- Siri formula is: BF = (4.95/? - 4.50) ÃÆ'â € "100
Analysis of bioelectric impedance
The Bioelectrical Impedance Analysis (BIA) method is a lower cost (from less than one to several hundred dollars in 2006) but a less accurate way to estimate the percentage of body fat. The general principle behind BIA: two or more conductors attached to one's body and a small electric current sent through the body. The resistance between the conductors will give a measure of body fat between a pair of electrodes, because resistance to electricity varies between adipose, muscle and skeletal tissue. Fat free mass (muscle) is a good conductor because it contains large amounts of water (about 73%) and electrolytes, while fat is anhydrous and poor conductor of electricity. Factors affecting the accuracy and accuracy of this method include instrumentation, subject matter, technician skills, and predictive equations formulated to estimate fat-free mass.
Each foot (bare) can be placed on the electrode, by now sending one foot, crossing the stomach and down the other. (For convenience, the instrument to be stepped on will also measure the weight.) Or, the electrodes can be held in each hand; calculation of fat percentage using weight, so it should be measured by scale and entered by the user. Both methods can provide different percentages, without inconsistencies, because they measure fat in different parts of the body. More sophisticated instruments for domestic use are available with electrodes for both feet and hands.
There is little scope for such technician error, but factors such as eating, drinking and exercising should be controlled because hydration levels are an important source of error in determining the flow of electric current to estimate body fat. Instructional instructions are usually advised not to take measurements immediately after drinking or eating or exercising, or when dehydrated. Instruments require details such as gender and age to be included, and use formulas that take this into account; for example, men and women store fat differently around the abdomen and thigh area.
Different BIA analyzes may vary. For example, when comparing the output of the Omega Body Logic Tanita scale to the Omron Body Logic , the Tanita scale estimates the percentage of body fat 40% higher in college-age men and 55% higher in women school age when compared to hydrostatic weighing. Population-specific equations are available for multiple instruments, making them more reliable.
Anthropometric method
There are various anthropometric methods for estimating body fat. The term anthropometric refers to measurements made from various parameters of the human body, such as the circumference of various body parts or the thickness of the skin folds. Most of these methods are based on statistical models. Some measurements are selected, and applied to population samples. For each individual in the sample, measurement methods are recorded, and individual body density is also recorded, which is determined by, for example, underwater weight, in combination with the multi-compartment body density model. From this data, a formula that connects body measurements with density is developed.
Since most anthropometric formulas such as the Durnin-Womersley skinfold method, the Jackson-Pollock skinfold method, and the US nose method, actually estimate the body density, not the percentage of body fat, the percentage of body fat is obtained by applying a second formula, such as Siri or Brozek described at the top of the density. As a result, the percentage of body fat calculated from skin folds or other anthropometric methods carries cumulative errors from the application of two separate statistical models.
Therefore, this method is lower than the direct measurement of body density and the application of only one formula to estimate the percentage of body fat. One way to consider these methods is that they trade accuracy for convenience, because it is much more convenient to measure multiple bodies rather than immersing an individual in water.
The main problem with all statistical derivative formulas is that in order to be widely applicable, they should be based on a large sample of individuals. However, it makes them inherently inaccurate. The ideal statistical estimation method for an individual is based on a sample of the same individual. For example, skin-based density formulas developed from men's rowers samples tend to be much more accurate to estimate the body density of a male rower's college than methods developed using samples from the general population, since the sample is narrowed down by age, the type sex, physical fitness level, type of exercise, and lifestyle factors. On the other hand, such formulas are not suitable for general use.
Skin fold method
The skin fold estimation method is based on a skin-fold test, also known as a pinch test, in which a pinch of skin is actually measured by calipers at some standard point on the body to determine the thickness of the subcutaneous fat layer. This measurement is converted to the estimated body fat percentage by equation. Some formulas require at least three measurements, others of seven. The accuracy of this estimate is more dependent on a person's unique body fat distribution than on the number of sites measured. In addition, it is important to test in the right location with fixed pressure. Although it may not provide an accurate reading of the percentage of real body fat, it is a reliable measure of changes in body composition over a period of time, provided the test is performed by the same person with the same technique.
Fat-based fat-based body fat is sensitive to the type of caliper used, and techniques. This method also only measures one type of fat: subcutaneous adipose tissue (fat under the skin). Two people may have almost the same size in all the skin fold sites, but differ greatly in their body fat levels due to differences in other body fat deposits such as visceral adipose tissue: fat in the abdominal cavity. Some models partially overcome this problem by including age as a variable in statistics and the resulting formula. Older people were found to have lower body densities for the same skinfold measurements, which are assumed to indicate a higher percentage of body fat. However, older, very athletic people may not fit this assumption, causing formulas to underestimate their body density.
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Ultrasound is widely used to measure tissue structure and has proven to be an accurate technique for measuring subcutaneous fat thickness. A-mode and B-mode ultrasound systems are now used and both rely on the use of tabulated values ​​of network voice speed and automatic signal analysis to determine the thickness of fat. By making measurements of thickness in some sites in your body can calculate the estimated percentage of body fat. Ultrasound techniques can also be used to measure muscle thickness directly and measure intramuscular fat. Ultrasound equipment is expensive, and is not only effective for body fat measurements, but if equipment is available, as in hospitals, the additional cost for measuring body fat is minimal.
Methods of height and circumference
There is also a formula to estimate the percentage of body fat from individual weight and thickness measurements. For example, the US Navy's peripheral method compares abdominal or hip and hip measurements with neck and height measurements as well as other sites claiming to estimate the percentage of a person's body fat with the conversion of a body mass index. In the US Navy this method is known as "string and choke." However, there is limited information, about the validity of the "string and choke" method because of its universal acceptance as inaccurate and easily falsified.
The US Army and the US Marine Corps are also dependent on altitude and circumference methods. For men, they measure the neck and waist just above the navel. Women are measured around the hips, waist, and neck. These measurements are then searched in published tables, with individual heights as additional parameters. This method is used because it is a cheap and convenient way to apply body fat tests throughout the service.
The roving method has little reception outside the Department of Defense because of their negative reputation compared to other methods. The accuracy of this method becomes a problem when comparing people with different body compositions, those with larger necks artificially result in lower body fat percentage calculations than those with smaller necks.
From BMI
Body fat can be estimated from body mass index (BMI), a person's mass in kilograms divided by the square of height in meters; If weight is measured in pounds and inches in height, the result can be converted to BMI by multiplying it by 703. There are a number of proposed formulas that link body fat to BMI. These formulas are based on work done by researchers published in peer-reviewed journals, but their correlation with body fat is only an estimate; body fat can not be inferred accurately from BMI.
Body fat can be estimated from body mass index with formulas derived by Deurenberg and co-workers. When making calculations, the relationship between the percentage of body fat determined by densitometry (BF%) and BMI should take into account age and gender. Internal and external validation of the prediction formula shows that they provide valid body fat estimates in men and women of all ages. However, on the subject of obesity, the prediction formula slightly exaggerates BF%. Predictive error is proportional to the prediction error obtained by other methods estimating BF%, such as measurement of skin fold thickness and bioelectrical impedance. The formula for children is different; the association between BMI and BF% in children was found to be different from that in adults because of the associated high BMI increase in children aged 15 years and younger.
Body fat child% = (1.51 ÃÆ'â € "BMI) - (0.70 ÃÆ'â €" Age) - (3,6 ÃÆ'â € "sex) 1,4
Lemak tubuh dewasa% = (1.20 ÃÆ'â € "BMI) (0.23 â €" Usia) - (10.8 ÃÆ'â € "seks) â €" 5.4
where sex is 1 for males and 0 for females.
Other indices can be used; the body's adiposity index is said by its developers to provide a direct estimate of the percentage of body fat, but statistical studies found this did not happen.
See also
- Adipose network
- Andreas MÃÆ'¼nzer
- Body fat gauge
- Body water
- Obesity classification
- Lizzie VelÃÆ'¡squez, a woman with "zero percent body fat"
References
External links
-
Gallagher, D; Heymsfield, SB; Heo, M; Jebb, SA; Murgatroyd, PR; Sakamoto, Y (2000). "Percentage of healthy body fat: An approach to developing guidelines based on body mass index". The American Journal of Clinical Nutrition . 72 (3): 694-701. PMIDÃ, 10966886.
Source of the article : Wikipedia
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