Body composition

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In physical fitness, body composition refers to quantifying the different components (or "compartments") of a human body. [1] The selection of compartments varies by model but may include fat, bone, water, and muscle. [2] Two people of the same gender, height, and body weight may have completely different body types as a consequence of having different body compositions. This may be explained by a person having low or high body fat, dense muscles, or big bones. [3]

Contents

Compartment models

Body composition models typically use between 2 and 6 compartments to describe the body. Common models include: [1]

As a rule, the compartments must sum to the body weight. The proportion of each compartment as a percent is often reported, found by dividing the compartment weight by the body weight. Individual compartments may be estimated based on population averages or measured directly or indirectly. Many measurement methods exist with varying levels of accuracy. Typically, the higher compartment models are more accurate, as they require more data and thus account for more variation across individuals. The four compartment model is considered the reference model for assessment of body composition as it is robust to most variation and each of its components can be measured directly. [1]

Measurement methods

A wide variety of body composition measurement methods exist. The gold standard measurement technique for the 4-compartment model consists of a weight measurement, body density measurement using hydrostatic weighing or air displacement plethysmography, total body water calculation using isotope dilution analysis, and mineral content measurement by dual-energy X-ray absorptiometry (DEXA). [1] However, it is also common to use a DEXA scan alone and refer to this as the "gold standard". [4] These claims are somewhat dubious since measurements methods vary significantly from study to study. In practice, the measurement methods used will be a tradeoff between cost, availability, and accuracy.

DEXA

Body composition measurement with dual energy X-ray absorptiometry (DEXA) is used increasingly for a variety of clinical and research applications. A DEXA scan requires medical supervision by a radiologist. Total body scans using DEXA give accurate and precise measurements of body composition, including bone mineral content (BMC), bone mineral density (BMD), lean tissue mass, fat tissue mass, and fractional contribution of fat. [5]

DEXA measurements are highly reproducible if the same type of machine is used, [6] making them excellent for monitoring pharmaceutical therapy, nutritional or exercise intervention, sports training, and other body composition altering programs. They are also fast, simple, non-invasive, and expose the subject to a level of x-rays less than that of a cross-country flight. DEXA exams provide both total body and up to 14 regional (trunk, individual arms & legs, android, gynoid, etc.) results. However, the role of DEXA in clinical evaluations and research studies has been questioned by Wang et al. [7] who stated that "the errors of the DXA [DEXA] method are still of concern if it were to be used as the criterion."

Hydrostatic weighing

Hydrostatic weighing, also referred to as underwater weighing, hydrostatic body composition analysis and hydrodensitometry, is a technique for measuring the density of a living person's body. It is a direct application of Archimedes' principle, that an object displaces its own volume of water.

Air displacement plethysmography

Body composition measurement with air displacement plethysmography or whole-body air displacement plethysmography (ADP) technology Adult body composition through air displacement plethysmography.jpg
Body composition measurement with air displacement plethysmography or whole-body air displacement plethysmography (ADP) technology

Air displacement plethysmography is an alternative to underwater weighing for measuring body volume. The technique uses air as opposed to water and is known as air displacement plethysmography (ADP). Subjects enter a sealed chamber that measures their body volume through the displacement of air in the chamber. Next, body volume is combined with body weight (mass) to determine body density. The technique then estimates the percentage of body fat and lean body mass (LBM) through empirically derived equations similar to those used with underwater weighing (for the density of fat and fat-free mass).

Isotope dilution analysis

Total body water may be effectively measured using isotope dilution analysis of deuterium oxide. [8]

Total body potassium

Potassium 40 is a naturally occurring radioactive isotope found in intracellular water, but is not present in stored triglycerides (fat). Whole body counting can measure the amount of potassium 40 (40K) in the body, a quantity called total body potassium (TBK). This can be used to estimate fat-free mass directly. It has mostly been replaced by newer, more accurate techniques such as DEXA. [9]

Bioelectrical impedance analysis

Another method to estimate body water is bioelectrical impedance analysis (BIA), which uses the resistance of electrical flow through the body. BIA is highly sensitive to hydration status and water intake. Drinking water dilutes the electrolytes in the body, making it less conductive, as does increasing body fat. By controlling hydration status or performing multiple impedance measurements, it is possible to estimate body fat and other variables.

InBody developed the world's first 8-point tactile electrode system in 1996, a direct segmental analysis method that measures the impedance of five torsos using multiple frequencies. Many BIA products provide partial muscle and fat mass measurements, but not impedance, especially in the torso. [10]

Recent advancements such as 8-point electrodes, multi-frequency measurements, and Direct Segmental Analysis, [11] have improved the accuracy of BIA machines. [12] BIA machines have found acceptance in medical, fitness, and wellness space owing to their ease-of-use, portability, quick measurements, and cost efficiency.

AURA Devices developed and launched a number of wearable bioimpedance trackers, including the first smart strap for Apple Watch that tracks body fat, muscles, lean mass, water levels, etc. [13]

Body Volume Index

The Body Volume Index (BVI) is a technique used for measuring body shape. Initially, BVI technology employed white light scanning machines to measure an individual's body shape. [14] However, recent technological advances in 3D measurement have enabled BVI to be calculated using images taken on a smartphone. Two images are required to create an individual 3D silhouette. By comparing this 3D silhouette with MRI data, body volume and fat distribution can be calculated.

Skin folds

Body composition can also be measured using the skin fold test, which is performed using a measuring caliper. It can be done in nine steps:

  1. Take measurements on the right side of the body.
  2. Mark client up.
  3. Pinch skin (KM) above mark
  4. Pull fat away from muscles
  5. Place caliper halfway between top and bottom of mark
  6. Allow caliper to settle (1–2 seconds)
  7. Take reading – repeat 15 seconds
  8. Add up total (4) – average
  9. Calculate body fat %

A common skin fold method is by using gun style calipers to measure the thickness of subcutaneous fat in multiple places on the body. This includes the abdominal area, the subscapular region, arms, buttocks and thighs. These measurements are then used to estimate total body fat.

Ultrasound

Ultrasound has also been used to measure subcutaneous fat thickness, and by using multiple points an estimation of body composition can be made. Ultrasound has the advantage of being able to also directly measure muscle thickness and quantify intramuscular fat. [15] In the abdomen, ultrasonography is a useful tool for quantifying both subcutaneous and visceral fat. [16] [17] Ultrasonography has many advantages over CT scan and MRI as it is non-invasive and doesn't utilize ionizing radiation, making it more accessible to special populations. [18]

Quantitative magnetic resonance

Quantitative magnetic resonance (QMR) applies a magnetic field to the body and measures the difference in relaxation rates of hydrogen atoms within fat versus lean mass. [19] It functions similarly to magnetic resonance imaging (MRI) but instead of providing an image like MRI, QMR gives quantities of fat mass, lean mass, and total body water. QMR is also widely used for body composition analysis of animals, including laboratory animals like mice, [20] and wildlife including birds. [21]

Circumferences and other simple measurements

Assessment of somatic (skeletal) protein is typically determined by simple measurements and calculations, including mid-arm circumference (MAC), mid-arm muscle circumference (MAMC), and creatinine height ratio (CHI). Creatinine height ratio is calculated as 24-hour urine creatinine multiplied by 100 over the expected 24-hour urine creatinine for height. This calculation results in a percentage that can indicate protein depletion. [22]

Many methods of determining body composition use the body weight as a measurement, determined via a weighing scale. Other details such as height and age can be correlated with other measures and are often used in estimation formulas.

Validity

The methods above are each valid and notable in providing a measurement that can be used to determine the "true body composition" of the tested individual. However, each method does possess its own individual limitations, such as accuracy, precision, or expense, and the combination of methods also has limitations. Often, the relative change from one period to the next is most important; if an individual can maintain all factors as similar as possible, even a simple method such as weighing may give enough information to determine the true change in composition. [23]

Types of exercises

The ideal percent of body mass which should be fat depends on an individual's sex, age, and physical activity. For example, a female thirty year old will have a different ideal fat percentage than a male thirty year old. An athlete will have a different ideal than a non athlete, and it can depend on the sport. [24]

The physical activities which can help decrease fat mass, increase lean mass, or both are the same for everybody. Aerobic exercise, also known as cardio (heart) exercise, decreases fat. High intensity interval training (HIIT) in particular helps decrease visceral fat. Visceral fat is near the internal organs, while subcutaneous fat is just under the skin. The former is more tightly associated with poor metabolic health. Bone and muscle strengthening exercise, also known as resistant training, decreases fat mass and increases lean mass at the same time, though it does better at the latter. In order to prevent injury from repetitive motion, people should do resistant training with different parts of their bodies on different days. [25]

See also

Related Research Articles

In physiology, body water is the water content of an animal body that is contained in the tissues, the blood, the bones and elsewhere. The percentages of body water contained in various fluid compartments add up to total body water (TBW). This water makes up a significant fraction of the human body, both by weight and by volume. Ensuring the right amount of body water is part of fluid balance, an aspect of homeostasis.

<span class="mw-page-title-main">Dual-energy X-ray absorptiometry</span> Diagnostic test for bone mineral density testing

Dual-energy X-ray absorptiometry is a means of measuring bone mineral density (BMD) using spectral imaging. Two X-ray beams, with different energy levels, are aimed at the patient's bones. When soft tissue absorption is subtracted out, the bone mineral density (BMD) can be determined from the absorption of each beam by bone. Dual-energy X-ray absorptiometry is the most widely used and most thoroughly studied bone density measurement technology.

<span class="mw-page-title-main">Adipose tissue</span> Loose connective tissue composed mostly by adipocytes

Adipose tissue is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells and a variety of immune cells such as adipose tissue macrophages. Its main role is to store energy in the form of lipids, although it also cushions and insulates the body.

<span class="mw-page-title-main">Adipocyte</span> Cells that primarily compose adipose tissue, specialized in storing energy as fat

Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. In cell culture, adipocyte progenitors can also form osteoblasts, myocytes and other cell types.

<span class="mw-page-title-main">Dielectric spectroscopy</span> A measuring tool

Dielectric spectroscopy measures the dielectric properties of a medium as a function of frequency. It is based on the interaction of an external field with the electric dipole moment of the sample, often expressed by permittivity.

<span class="mw-page-title-main">Underweight</span> Below a weight considered healthy

An underweight person is a person whose body weight is considered too low to be healthy. A person who is underweight is malnourished.

The anthropometry of the upper arm is a set of measurements of the shape of the upper arms.

The body fat percentage of an organism is the total mass of its fat divided by its total body mass, multiplied by 100; body fat includes essential body fat and storage body fat. Essential body fat is necessary to maintain life and reproductive functions. The percentage of essential body fat for women is greater than that for men, due to the demands of childbearing and other hormonal functions. Storage body fat consists of fat accumulation in adipose tissue, part of which protects internal organs in the chest and abdomen. A number of methods are available for determining body fat percentage, such as measurement with calipers or through the use of bioelectrical impedance analysis.

Bioelectrical impedance analysis (BIA) is a method for estimating body composition, in particular body fat and muscle mass, where a weak electric current flows through the body, and the voltage is measured in order to calculate impedance of the body. Most body water is stored in muscle. Therefore, if a person is more muscular, there is a high chance that the person will also have more body water, which leads to lower impedance. Since the advent of the first commercially available devices in the mid-1980s the method has become popular, owing to its ease of use and portability of the equipment. It is familiar in the consumer market as a simple instrument for estimating body fat. BIA actually determines the electrical impedance, or opposition to the flow of an electric current through body tissues, which can then be used to estimate total body water (TBW), which can be used to estimate fat-free body mass and, by difference with body weight, body fat.

In medicine, the urea-to-creatinine ratio (UCR), known in the United States as BUN-to-creatinine ratio, is the ratio of the blood levels of urea (BUN) (mmol/L) and creatinine (Cr) (μmol/L). BUN only reflects the nitrogen content of urea and urea measurement reflects the whole of the molecule, urea is just over twice BUN. In the United States, both quantities are given in mg/dL The ratio may be used to determine the cause of acute kidney injury or dehydration.

<span class="mw-page-title-main">Bone density</span> Amount of bone mineral in bone tissue

Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone, although clinically it is measured by proxy according to optical density per square centimetre of bone surface upon imaging. Bone density measurement is used in clinical medicine as an indirect indicator of osteoporosis and fracture risk. It is measured by a procedure called densitometry, often performed in the radiology or nuclear medicine departments of hospitals or clinics. The measurement is painless and non-invasive and involves low radiation exposure. Measurements are most commonly made over the lumbar spine and over the upper part of the hip. The forearm may be scanned if the hip and lumbar spine are not accessible.

<span class="mw-page-title-main">Overweight</span> Above a weight considered healthy

Being overweight is having more body fat than is optimally healthy. Being overweight is especially common where food supplies are plentiful and lifestyles are sedentary.

Lean body mass (LBM), sometimes conflated with fat-free mass, is a component of body composition. Fat-free mass (FFM) is calculated by subtracting body fat weight from total body weight: total body weight is lean plus fat. In equations:

Electrical impedance myography, or EIM, is a non-invasive technique for the assessment of muscle health that is based on the measurement of the electrical impedance characteristics of individual muscles or groups of muscles. The technique has been used for the purpose of evaluating neuromuscular diseases both for their diagnosis and for their ongoing assessment of progression or with therapeutic intervention. Muscle composition and microscopic structure change with disease, and EIM measures alterations in impedance that occur as a result of disease pathology. EIM has been specifically recognized for its potential as an ALS biomarker by Prize4Life, a 501(c)(3) nonprofit organization dedicated to accelerating the discovery of treatments and cures for ALS. The $1M ALS Biomarker Challenge focused on identifying a biomarker precise and reliable enough to cut Phase II drug trials in half. The prize was awarded to Dr. Seward Rutkove, chief, Division of Neuromuscular Disease, in the Department of Neurology at Beth Israel Deaconess Medical Center and Professor of Neurology at Harvard Medical School, for his work in developing the technique of EIM and its specific application to ALS. It is hoped that EIM as a biomarker will result in the more rapid and efficient identification of new treatments for ALS. EIM has shown sensitivity to disease status in a variety of neuromuscular conditions, including radiculopathy, inflammatory myopathy, Duchenne muscular dystrophy, and spinal muscular atrophy.

<span class="mw-page-title-main">Classification of obesity</span> Overview of the classification of the condition of obesity

Obesity classification is a ranking of obesity, the medical condition in which excess body fat has accumulated to the extent that it has an adverse effect on health. The World Health Organization (WHO) classifies obesity by body mass index (BMI). BMI is further evaluated in terms of fat distribution via the waist–hip ratio and total cardiovascular risk factors. In children, a healthy weight varies with sex and age, and obesity determination is in relation to a historical normal group.

<span class="mw-page-title-main">Air displacement plethysmography</span> Human body composition measurement method

Air displacement plethysmography is a recognized and scientifically validated densitometric method to measure human body composition. ADP is based on the same principles as the gold standard method of hydrostatic weighing, but through a densitometric technique that uses air displacement rather than water immersion. Air-displacement plethysmography offers several advantages over established reference methods, including a quick, comfortable, automated, noninvasive, and safe measurement process, and accommodates various subject types.

Dual X-ray absorptiometry and laser technique (DXL) in the area of bone density studies for osteoporosis assessment is an improvement to the DXA Technique, adding an exact laser measurement of the thickness of the region scanned. The addition of object thickness adds a third input to the two x-ray energies used by DXA, better solving the equation for bone and excluding more efficiently these soft tissues components.

Single photon absorptiometry is a measuring method for bone density invented by John R. Cameron and James A. Sorenson in 1963.

John A. Shepherd is an American physicist, professor of epidemiology and population sciences and director of the Shepherd Research Laboratory at the University of Hawaii Cancer Center in Honolulu, Hawaii. He is an expert in the use of dual-energy X-ray absorptiometry (DXA) for quantitative bone and soft tissue imaging, and pioneered the use of 3D optical imaging of the whole body for quantifying body composition and associated diseases including cancer risk, obesity, diabetes, and frailty. In 2016, he was the President of the Board of the International Society for Clinical Densitometry.

Paul Deurenberg is a Dutch retired academic, nutritional biochemist and consultant. He was a former associate professor in the Department of Human Nutrition at Wageningen University (WU), and is most known for his research expertise in the areas of energy metabolism, food consumption, and body composition studies.

References

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  3. ↑ "Body Composition Tests". www.heart.org. Retrieved 2015-11-25.
  4. ↑ Scafoglieri, A; Clarys, JP (August 2018). "Dual energy X-ray absorptiometry: gold standard for muscle mass?". Journal of Cachexia, Sarcopenia and Muscle. 9 (4): 786–787. doi: 10.1002/jcsm.12308 . PMC   6104103 . PMID   29786955. S2CID   29152747.
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  16. ↑ Kim, Jihyun; Kim, Keunyoung (2023-12-18). "Author Correction: CT-based measurement of visceral adipose tissue volume as a reliable tool for assessing metabolic risk factors in prediabetes across subtypes". Scientific Reports. 13 (1). doi:10.1038/s41598-023-49371-z. ISSN   2045-2322.
  17. ↑ Störchle, Paul; Müller, Wolfram; Sengeis, Marietta; Lackner, Sonja; Holasek, Sandra; Fürhapter-Rieger, Alfred (2018-11-02). "Measurement of mean subcutaneous fat thickness: eight standardised ultrasound sites compared to 216 randomly selected sites". Scientific Reports. 8 (1): 16268. doi:10.1038/s41598-018-34213-0. ISSN   2045-2322.
  18. ↑ Kim, Jihyun; Kim, Keunyoung (2023-10-20). "CT-based measurement of visceral adipose tissue volume as a reliable tool for assessing metabolic risk factors in prediabetes across subtypes". Scientific Reports. 13 (1): 17902. doi:10.1038/s41598-023-45100-8. ISSN   2045-2322.
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  25. ↑ "Examples of Body Composition Exercises". Healthy Living - azcentral.com. Retrieved 2015-11-25.
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