Body Fat Measurements That Are Most Accurate And Reliable

By examining the scientific literature, the percentage of body fat considered acceptable (normal range) is found between 10% and 18% for men and between 18% and 26-28% for women. The different percentage of body fat between men and women is determined by the greater quantity of ‘essential’ fat of women (12% against 3-5% of man) and by the different hormonal material (which favors a greater accumulation of lean mass in ‘man). In the female population, fat mass is typically concentrated in the breasts and hips; this is why it is functional for pregnancy and breastfeeding. By measuring the body fat percentage correctly, doctor will be able to determine the severity of condition and appoint a more suitable treatment combined with appropriate lifestyle changes.

Body fat percentage

Primary or essential fat represents the amount of fat contained in the central nervous system, in the bone marrow, in the mammary glands, in the kidney, in the spleen and in other tissues. Given the particular anatomical localization, essential fat has a physiological role of primary importance, to the point of being considered the minimum percentage of fat mass compatible with a state of good health.

When the percentage of body fat decreases until it is reduced only to the amount of essential fat or slightly more, the body suffers; for example, there is a greater susceptibility to infections in humans and amenorrhea, often accompanied by osteopenia, in women.

The deposit fat – which added to the primary fat gives us the total body fat – is concentrated at the subcutaneous, thoracic – abdominal (visceral), intra and intermuscular levels. Compared to the general population, the percentages of body fat desirable for physically active subjects, and even more so for high-level athletes, are generally lower.

Normal values

Percentage of total body fat for the different categories of subjects

Physical formMenWomen
Athletes5,0 – 13,012,0 – 22,0
Physically active persons12,0 – 18,016,0 – 25,0
Slightly overweight19,0 – 24,026,0 – 31,0
Obese> 24,0> 31,0

To measure the percentage of body fat different methods have been developed:

  • plicometry
  • bioimpedance
  • body surface and body fat calculation
  • BMI and percentage of body fat

Plicometry is one of the most accurate methods for assessing body composition. Among the various methods of measuring the percentage of body fat, plicometry is one of the simplest, most accurate and with the purchase costs of the instruments contained.

Plicometer is an instrument that can be compared to a mechanic’s caliber as it consists essentially of a caliper and a graduated scale that measures the distance between the tips. Plicometer should exert a constant pressure between the folds of 10g / mm ² (if the pressure is different, the non-optimal compression of plicometer will cause errors in the detection phase). It is therefore advisable to periodically check the gauge according to the manufacturer’s instructions (pressure, distance from the tips). As we saw in the introductory part there are various types ranging from the cheapest plastic, not suitable for scientific surveys, to the more professional metal. The latter are the most used in the anthropometric field and are essentially three: Lange USA, 65mm; Harpenden GB 55 mm, Holtain 50 mm (1 mm is the measure of maximum opening of the clamps).

The type of gauge used introduces an error in the measurement:

CaliberJackson-PollockDurin-Womersley
Lange23,4%26,9%
Harpeden19,6%23,8%
Note

The calculation of fat mass was done using the Lohman equations

Analyzing the following table we can appreciate how between one type of caliber and the other (to note that both are scientific gauges) there is an error of about 15%. This data is a further confirmation that there are no 100% precise methods in assessing body composition; in fact only the dissection of the body would give correct results but we believe that none of you want to undergo this method!

The correct detection technique is fundamental in order not to introduce further measurement errors. Therefore the following guidelines must be respected:

Make measurements on the left side of the body by convention (without taking into account the side of preference of the subject, unless the left is not impossible or you want to detect both or only the right for rehabilitation problems). On the other hand, there are also authors in the literature who advise to make the measurements on the right side of the body.

1. Locate the site and mark with dermographic lapis

2. Hold the caliber with the right hand and grab a fold between the thumb and forefinger of the left hand, trying to unstick the underlying muscle tissue.

3. The fingers must be 8 cm apart, on a line perpendicular to the longitudinal axis of the panniculus.

4. Exercise with the right hand a pressure to separate the branches of the caliber, apply the caliber to the base holding it at 90 °.

5. Always keep the fold between your fingers and release the gauge pressure slowly.

6. Perform the reading after 2 seconds.

7. Open the gauge, remove it and close it slowly.

8. Repeat the measurement 2 times (with at least 2 minutes interval to allow the fold to return to the incompressed form) and then average. If the two measurements vary more than 10%, a third must be performed.

The measurement of adipose folds can be performed in different locations, the most used are the fold sites:

The measurement of adipose folds> Chest: the fold is taken in a diagonal direction between the armpit and the nipple;

> Subscapularis: the fold is taken diagonally, at the lower corner of the scapula;

> Axillary: the fold is taken horizontally below the area covered with hairs;

> Suprailliac: the fold is taken obliquely, just above the iliac crest;

> Abdominal: the fold is taken vertically (or horizontal depending on the authors), 2 cm lateral to the navel;

> Triceps: the fold is taken vertically, in the middle of the measured flexed arm;

> Biceps: the fold is taken vertically, halfway across the measured arm;

> Thigh: the fold is taken vertically, at the center of the distance between the inguinal fold and the patella;

> Calf: the fold is taken vertically, at the point of greatest development of the part and in its medial portion;


The errors that can be committed during the survey

Are very many and it is important to know them in order to reduce them as much as possible. The following are all the possible causes of errors.

 1. Operator’s skill

Operator’s skillThe incorrect location of the plots causes errors in the measure:

  • Intra-observer error: error associated to the same detector on repeated measurements on the same subject. It varies with the site and is greater for abdomen (8.8%) and thigh (7.1%) because in these sites the quantity of subcutaneous adipose tissue is greater. Amount of fat in the subject: the more a subject is fat and the more difficult the detection becomes; in fact, in obese and very muscular individuals the subcutaneous adipose tissue does not easily separate from the underlying muscle. Moreover, in the obese the thickness of the folds exceeds the maximum opening of the caliber. The only alternative is to take sites where the subcutaneous adipose tissue is minimal (biceps).
  • Inter-observer error: error associated with different detectors. The objectivity of the measures improves when the detectors follow standardized procedures, they practice together and mark the sites.

2. Type of caliber

Check: Accuracy, measuring range and pressure. Use the same gauge for repeated measurements on the same subject.

Thickness of the skin (0.5-2 mm). Compressibility of adipose tissue. Hydration level. Do not measure after workout, sauna, Turkish bath, swimming or shower because exercise, hot water and heat produce hyperaemia (increased blood flow) in the skin with consequent increase in skin thickness.

4. Predicting equations used: there are two classes of equations:

  • specific population equations, derived from a limited and homogeneous sample and applicable exclusively to a specific population (for example in the assessment of body composition of cyclists).
  • generalized equations, derived from large heterogeneous samples that vary in age and adiposity (e,g. assessment of body composition of Americans)

Jackson and Pollock equations: they developed two different equations: three and seven fold.


Three folds: pectoral, abdominal, front of the thigh; in women: tricipital, supra-iliac, anterior thigh.

Seven folds: pectoral, middle axillary, tricipital, subscapular, suprailiac, abdominal, anterior thigh.


The Jackson and Pollock three-fold equation is used to evaluate the body composition of the athletes. The seven-fold Jackson and Pollock equation is used to evaluate body composition in the general population.

How is an individual’s body constitution established?

The body constitution of a subject is established by detecting its skeletal diameters and comparing them with those of the reference population. These surveys, which lead to classifying individuals into three categories (slim constitution, medium constitution and robust constitution), are normally performed at the wrist, elbow, shoulder, hip and knee levels.

measuring the circumference of the right wristFor example, it is possible to establish body constitution by measuring the width of the right elbow with a caliber. In this case it is important that the reference points are palpable (for the obese is not indicated) and that the branches of the caliber exert a moderate pressure on the two ends of the bone segment.

At the home level, however, body constitution can be calculated by measuring the circumference of the right wrist. This detection must be carried out with a flexible but anaelastic metric cord, to be positioned at the base of the wrist as shown in the figure (immediately under the styloid processes of the radio and of the ulna).

Definition of body size based on elbow width (Frisancho method)

Body constitutionElbow width (cm)
MenWomen
Slim constitution< 6.9< 5.9
Medium constitution6.9 – 7.65.9 – 6.6
Robust constitution> 7.6> 6.6

Definition of body size based on the circumference of the wrist:

Body constitutionWrist circumference
MenWomen
Ectomorph (slender)> 20 cm> 18 cm
Mesomorph16- 20 cm14 – 18 cm
Endomorph (robust)< 16< 14

For a more precise evaluation, the following equation is used wrist circumference morphology The data obtained must then be compared with the references listed in the table.

Bioimpedance is one of the most precise and fast methods for assessing body composition. Bioimpedentiometry is a fast and accurate method for assessing the body composition (BC) of the human being. The analysis of body composition is used in various fields, such as: medicine, anthropology, ergonomics, sport, auxology.

Recently, specialists have channeled energy and resources in deepening the correlation between BC, health status and sports performance; it has emerged that a body composition tendentially rich in adipose tissue (especially with abdominal distribution or even worse intra-abdominal), and poor in muscle mass, is related to a poor overall fitness (cardio-circulatory, respiratory, muscular, articular, etc.), a poor athletic-sporting ability and a greater physical risk linked to unfortunate events such as hypertension, diabetes, obesity, dyslipidemia, metabolic syndrome, cardio-vascular complications, joint diseases… and premature death.

2 compartments To deepen the knowledge of body composition it is necessary to be clear that the organism, from the compositional point of view, can be divided into compartments. There is no single classification and at least five can be described:

2 compartments (fat mass / lean mass – FM / FFM)

The body structure must be considered as a growing organization of complexity; the various levels of analysis are: atoms, molecules, cells, tissues, organs, systems / apparatuses and the whole body. Knowledge of the relationships between different constituents at a given level or between different levels is important for the indirect estimation of a specific body compartment.

Whole body analysis – BMI

The body can be considered as a single unit characterized by: size, shape, area and surface, density and other external characteristics (weight, height, volume); in the analysis of BMI the atomic and cellular levels are of relative interest, therefore, the organization system is reduced mainly to the levels:

  • Molecular – chemical
  • Tissue – anatomic.
  • Methods: validity and accuracy

Validity is the degree to which an instrument or method actually measures what it says to measure; at the basis of the validity lies the accuracy, that is the precision of the measurement of a quantity whose real value is known.

Whole body analysis – BMIIn the evaluation of the BC (therefore of the fat mass – FM) the levels of validity are 3:

  1. 1st level – direct: dissection of corpses and extraction of fat with ether
  2. 2d level – partially direct: measurement of ‘some’ quantities by densitometry (DXA) and subsequent quantitative report for FM estimation
  3. 3d level – indirect: detection of a measurement (such as a thickness or electrical resistance) and derivation of a regression equation on the II level (in reality it would be better to define it doubly indirect).

Plyometrics and bio-impedancemetry are methods belonging to the three level of validity and therefore indirect; they are highly ‘specific samples’ because the relationship between fat and density depends on many variables such as: body hydration, body density, muscularity, compressibility and fat thickness, fat distribution, quantity of abdominal fat.

Bio-impedancemetry is based on the concept of bioelectrical impedance, i.e. the relationship between the amplitude of an alternating potential and the consequent amplitude of the alternating current in a biological conductor.The concept of bioelectrical impedance was deepened by Lukaski, in 1985 where Z = opposition of a biological conductor to an alternating current.

Bioimpedentiometry is a method of assessing indirect BC, a dependent sample but with numerous advantages and advantages; among these we recognize: rapidity of execution, ease of use, non-invasiveness, more economical than DXA (densitometry), which can be designed both for the clinic and for field surveys (transportable).

Bio-impedancemetry measures the impedance offered by a body to the passage of an alternating current at low intensity (800μA) and fixed frequency; the thin tissues conduct the fixed current more than the fat tissues because they contain a greater quantity of water and electrolytes. It follows that the conduction capacity is directly proportional to the amount of water and electrolytes contained. Moreover, the TBW can be predicted by impedance (Z) because the electrolytes contained in the water are good conductors of electric current; if the TBW is large, the current flows easily through the body with less resistance (R), which in itself appears inversely proportional to the lean mass (FFM). By logic, resistance is directly proportional (high) in individuals with greater amounts of fatty tissue because fat is a very poor current conductor because of its low water content.

Bio-impedancemetry and body forms

The human body is not a single cylinder with uniform cross-section and must be interpreted as five distinct cylinders and connected in series; the various segments are not uniform neither in length nor in section, therefore the resistance is variable.

There is also a relationship between the opposition of a biological conductor to an alternating current (Z) and the length and volume of the conductor; the impedance (Z) to the flow of current through the body is directly proportional to the length of the conductor (stature) and inversely proportional to the section, always taking into account that: impedance (Z) = ƿ (resistivity) [length (L) / section (A)] – where ƿ is equal to the specific resistivity of the body tissues (constant).

Bio-impedancemetry and physical principles

The biological tissues act as conductors or insulators and the flow of current follows a path of least resistance. The use of bio-impedancemetry to evaluate the BC is based on various conductive and dielectric properties of biological tissues, with variations in the frequency referred to the electric current; tissues that contain water and electrolytes such as cerebrospinal fluid, blood and muscles are good conductors, while fat, bone, and air-filled spaces like the lungs are dielectric fabrics. In the human body, the volume (V) of these tissues can be deduced from the measure of their resistance (R).

Impedance is a function of resistance (R) and reactance (Xc): Z = R2 + Xc2

The impedance (Z) is the opposition dependent on the resistance of a conductor to the flow of an alternating electric current and is decomposable into two members: resistance (R) and reactance (Xc). Resistance (R) is the pure measure of opposition to the flow of electric current and is inverse to conductance. The reactance (Xc) is the opposition to the flow of current caused by the body mass (MC) and is the reciprocal of the capacitance; in bio-impedancemetry, resistance (R) and impedance (Z) are interchangeable because the reactance (Xc) is very low (<4%). At 50Hz, the resistance (R) is greater than the reactance (Xc) so the resistance (R) is the best predictor of the impedance (Z).

The resistance index corresponds to: stature (S) 2 / resistance (R), while the best predictor of extra cellular water (ECW) is: stature (H) 2 / reactance (Xc).

The resistance (R) between two points is defined by the Ohm’s law: resistance (R) = distance between two points (V) / current intensity (I).

As anticipated, for an isotropic cylindrical conductor, the resistance (R) is directly proportional to the length (L) and inversely proportional to its section (A), therefore, the specific resistivity (ƿ) of the trunk is 2 or 3 times higher than the resistivity (ƿ) of that of the extremities. Also the resistivity (ƿ) of adults is greater than in children and the resistivity (ƿ) of the obese is greater than in the normal weight.

Bioimpedanceometry – error factors

The ‘acceptable’ error level for a BC analysis after bioimpedance is

Bioimpedanceometry – error factorsThe level of accuracy and precision of the bioimpedance method is mainly influenced by intra-instrumental variability (calibration) and inter-instrumental variability (different models).

In monofrequency impedances, the intensity of the alternating current (800: 500 μA) can vary considerably even at the same 50KHz frequency, as well as the prediction equation (software diversity) and the type of calibration (internal or external).

The multifrequency impedance meters have prices certainly higher than those at monofrequency; they use a tri-frequency (5-50-100KHz) to measure resistance (R) and reactance (Xc), but they are mainly used in scientific research.

Ultimately, to obtain useful measurements for the evaluation of a subject’s BC it is always necessary to use the same instrument and calibrate it before use. Better to use electrodes with a surface of 5cm2 and place them in full-body mode (distal / proximal).

It is also appropriate to specify that there are paraphysiolhic conditions that can alter the detection of body composition. The first is the state of hydration; it has been observed that a solid and liquid fasting state of at least 5 hours is able to modify the detection on the subject. Similarly, intense aerobic exercise can result in a reduction in resistance (R) due to imbalance between body electrolytes and total water; a relationship in favor of electrolytes with respect to water leads to greater conductivity. Body temperature also significantly affects the detection with bioimpedanceometry; increasing it there is a reduction in resistance (R), therefore, with pyrexia or hyperthermia, bioimpedance is NOT reliable. Finally, the skin on which the electrodes are applied increases its conductivity if cleaned with ethyl alcohol.

Note

Errors of 1 cm in the positioning of the electrodes in the body determines a modification of the detection equal to 2% of the total, as well as the ambient temperature

Benefits of bio-impedancemetry compared to plicometry

Both the plicometry and the bioimpedanceometry are indirect BC detection techniques and have the same degree of accuracy; however, sometimes it would be preferable to use bioimpedanceometry as it has some application advantages.

Benefits of bio-impedancemetry compared to plicometryAmong these we mention:

  • It does not require a high degree of manual skills and skill of the operator
  • It is more comfortable
  • It can be estimated for the evaluation of the obese and bedridden
  • It also evaluates the local BC
  • It has the possibility to evaluate the ECW (extracellular water) and the ICW (intracellular water)

In short: a better survey is achieved with bioimpedanceometry

To perform a correct bioimpedance measurement it is necessary to:

  • Place the electrodes correctly (4 cm distal black proximal red distal)
  • Recognize dehydration
  • Evaluate the importance of the physical exercise performed
  • Establish a thermally suitable detection environment
  • Clean the conduction surface
  • Furthermore, remember that to obtain reliable and repeatable data the subject must:
  • Be fasting for at least 4 hours
  • Being abstinent from exercise for at least 12 hours
  • Having an empty bladder
  • Being abstinent from alcohol for at least 48 hours
  • Being abstinent from diuretics for at least 7 days

If we want to be even more precise, we should remember that the pre-menstrual period in women determines a change in the body’s balance and that the change in water content and saline in children requires the use of specific prediction equations.

According to some researchers the accuracy of prediction with BIA can be improved by using:

  • Eq. age-specific Lohman 1992
  • Eq. breed-specific Rising et al., 1991
  • Eq. specific for level of adiposity Rye t al., 1988
  • Eq. specifications for physical activity level Houtkooper 1989

Generalized equations have been formulated that include age and sex but it is also possible that overestimates the fat mass in individuals with low percentage of fat mass (the opposite of the plicometria) and underestimates the fat mass in high percentage individuals.

Body surface

Body surfaceThe body surface area (Body Surface Area) is a very important anthropometric parameter; knowing it, it is in fact possible to draw up specific nutritional or pharmacotherapeutic programs (the dosage of certain medicines is expressed in mg per m2 of BSA). With respect to weight, the body surface area is a better indicator of metabolic mass, because it is less influenced by the amount of adipose tissue. In adults, moreover, the body surface is approximately proportional to the glomerular filtration surface, to the volume, to the cardiac dimensions and to other cardiological parameters.

Mosteller (standard, because easy to remember):

Body Surface Area (m2) = [(Height (cm) X Weight (kg) / 3600)] 1/2

DuBois and DuBois:

Body Surface Area (m2) = 0.202 * (Height (m) 0.725 * Weight (kg) 0.425)Body

Surface Area (m2) = 0.007184 * (Height (cm) 0.725 * Weight (kg) 0.425)

Haycock (in children):

Body Surface Area (m2) = 0.024265 * Height (cm) 0.3964 * Weight (kg) 0.5378

Gehan and George:

Body Surface Area (m2) = 0.0235 * Height (cm) 0.42246 * Weight (kg) 0.51456

Boyd:

C. (m2) = 0.0003207 * Height (cm) 0.3 * Weight (g) (0.7285 – (0.0188 x LOG (g))

The higher the body surface, the higher the heat loss (which occurs mainly at this level). For this reason nature has wisely made sure that the Eskimos developed particularly short legs (lower body surface), with a stocky structure (greater heat production), unlike the blacks, who have long arms and legs to disperse more heat and a short bust to produce less.

Basal metabolic rate increases with increasing body surface area (for this reason it is normally expressed in Kcal / m2 / hr). This is a very important observation, since a diet suitable for a long-limbed person (long limbs), becomes fat when offered to another of equal weight, but of considerably less stature. Basal metabolism can be calculated based on body surface using:

Fleisch’s formula

  • BMR (man) = 24 * BSA * {35.5 – 0.064 * [age (years) – 20]}
  • BMR (woman) = 24 * BSA * {38 – 0.073 * [age (years) – 20]}
  • BMI and body fat percentage

The following equations allow to calculate the indicative percentage of body fat starting from the BMI value. The BMI is obtained by dividing its weight in Kg with the square of the height expressed in meters.

Example: If your weight is 90 kg and you are 190 cm tall, your BMI. is: 90 / (1.9 x 1.9) = 24.9

The percentage of body fat calculated overestimates the fat mass in athletes, especially those with high muscle mass (see: the limits of BMI in the assessment of body composition).

The following equations allow to calculate the indicative percentage of body fat starting from the BMI value. The BMI is obtained by dividing its weight in Kg with the square of the height expressed in meters.

Example: If your weight is 90 kg and you are 190 cm tall, your BMI. is: 90 / (1.9 x 1.9) = 24.9

The percentage of body fat calculated overestimates the fat mass in athletes, especially those with high muscle mass (see: the limits of BMI in the assessment of body composition).

the following formulas:
  • Deurenberg formula Body fat% = (1.20 x BMI) + (0.23 x age) – (10.8 x sex) – 5.4
  • Deurenberg Body Fat Formula% = (1.29 x BMI) + (0.20 x age) – (11.4 x sex) – 8.0
  • Gallagher formula Body fat% = (1.46 x BMI) + (0.14 x age) – (11.6 x sex) – 10
  • Jackson-Pollock Body Fat Formula% = (1.61 x BMI) + (0.13 x age) – (12.1 x sex) – 13.9
  • sex = 1 if male; sex = 0 if female.
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