This is an accepted version of this page
122-477: Body mass index ( BMI ) is a value derived from the mass ( weight ) and height of a person. The BMI is defined as the body mass divided by the square of the body height , and is expressed in units of kg/m, resulting from mass in kilograms (kg) and height in metres (m). The BMI may be determined first by measuring its components by means of a weighing scale and a stadiometer . The multiplication and division may be carried out directly, by hand or using
244-402: A displacement R AB , Newton's law of gravitation states that each object exerts a gravitational force on the other, of magnitude where G is the universal gravitational constant . The above statement may be reformulated in the following way: if g is the magnitude at a given location in a gravitational field, then the gravitational force on an object with gravitational mass M is This
366-405: A net force is applied. The object's mass also determines the strength of its gravitational attraction to other bodies. The SI base unit of mass is the kilogram (kg). In physics , mass is not the same as weight , even though mass is often determined by measuring the object's weight using a spring scale , rather than balance scale comparing it directly with known masses. An object on
488-579: A BMI between the 85th and 95th percentile are considered to be overweight. Studies in Britain from 2013 have indicated that females between the ages 12 and 16 had a higher BMI than males of the same age by 1.0 kg/m on average. These recommended distinctions along the linear scale may vary from time to time and country to country, making global, longitudinal surveys problematic. People from different populations and descent have different associations between BMI, percentage of body fat, and health risks, with
610-400: A BMI of 25 or more is considered overweight and 30 or more is considered obese . In addition to the principle, international WHO BMI cut-off points (16, 17, 18.5, 25, 30, 35 and 40), four additional cut-off points for at-risk Asians were identified (23, 27.5, 32.5 and 37.5). These ranges of BMI values are valid only as statistical categories. BMI is used differently for people aged 2 to 20. It
732-406: A bronze ball and a wooden ramp. The wooden ramp was "12 cubits long, half a cubit wide and three finger-breadths thick" with a straight, smooth, polished groove . The groove was lined with " parchment , also smooth and polished as possible". And into this groove was placed "a hard, smooth and very round bronze ball". The ramp was inclined at various angles to slow the acceleration enough so that
854-654: A calculator, or indirectly using a lookup table (or chart). The table displays BMI as a function of mass and height and may show other units of measurement (converted to metric units for the calculation). The table may also show contour lines or colours for different BMI categories. The BMI is a convenient rule of thumb used to broadly categorize a person as based on tissue mass ( muscle , fat , and bone ) and height. Major adult BMI classifications are underweight (under 18.5 kg/m), normal weight (18.5 to 24.9), overweight (25 to 29.9), and obese (30 or more). When used to predict an individual's health, rather than as
976-790: A constant gravitational field, the weight of an object is proportional to its mass, and it is unproblematic to use the same unit for both concepts. But because of slight differences in the strength of the Earth's gravitational field at different places, the distinction becomes important for measurements with a precision better than a few percent, and for places far from the surface of the Earth, such as in space or on other planets. Conceptually, "mass" (measured in kilograms ) refers to an intrinsic property of an object, whereas "weight" (measured in newtons ) measures an object's resistance to deviating from its current course of free fall , which can be influenced by
1098-482: A curved path. "For a stone projected is by the pressure of its own weight forced out of the rectilinear path, which by the projection alone it should have pursued, and made to describe a curve line in the air; and through that crooked way is at last brought down to the ground. And the greater the velocity is with which it is projected, the farther it goes before it falls to the Earth." Newton further reasons that if an object were "projected in an horizontal direction from
1220-415: A death rate similar to normal weight people as defined by BMI, while underweight and obese people had a higher death rate. A study published by The Lancet in 2009 involving 900,000 adults showed that overweight and underweight people both had a mortality rate higher than normal weight people as defined by BMI. The optimal BMI was found to be in the range of 22.5–25. The average BMI of athletes
1342-472: 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. 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
SECTION 10
#17327901606301464-462: A force from a scale or the surface of a planetary body such as the Earth or the Moon . This force keeps the object from going into free fall. Weight is the opposing force in such circumstances and is thus determined by the acceleration of free fall. On the surface of the Earth, for example, an object with a mass of 50 kilograms weighs 491 newtons, which means that 491 newtons is being applied to keep
1586-399: A friend, Edmond Halley , that he had solved the problem of gravitational orbits, but had misplaced the solution in his office. After being encouraged by Halley, Newton decided to develop his ideas about gravity and publish all of his findings. In November 1684, Isaac Newton sent a document to Edmund Halley, now lost but presumed to have been titled De motu corporum in gyrum (Latin for "On
1708-537: A given height. The BMI also fails to take into account loss of height through ageing. In this situation, BMI will increase without any corresponding increase in weight. Assumptions about the distribution between muscle mass and fat mass are inexact. BMI generally overestimates adiposity on those with leaner body mass (e.g., athletes) and underestimates excess adiposity on those with fattier body mass. A study in June 2008 by Romero-Corral et al. examined 13,601 subjects from
1830-481: A good general correlation with body fat percentage, and noted that obesity has overtaken smoking as the world's number one cause of death. But it also notes that in the study 50% of men and 62% of women were obese according to body fat defined obesity, while only 21% of men and 31% of women were obese according to BMI, meaning that BMI was found to underestimate the number of obese subjects. A 2010 study that followed 11,000 subjects for up to eight years concluded that BMI
1952-421: A gravitational field. Newton further assumed that the strength of each object's gravitational field would decrease according to the square of the distance to that object. If a large collection of small objects were formed into a giant spherical body such as the Earth or Sun, Newton calculated the collection would create a gravitational field proportional to the total mass of the body, and inversely proportional to
2074-406: A hammer and a feather are dropped from the same height through the air on Earth, the feather will take much longer to reach the ground; the feather is not really in free -fall because the force of air resistance upwards against the feather is comparable to the downward force of gravity. On the other hand, if the experiment is performed in a vacuum , in which there is no air resistance, the hammer and
2196-657: A high muscle-to-fat ratio and therefore a BMI that is misleadingly high relative to their body-fat percentage. A common use of the BMI is to assess how far an individual's body weight departs from what is normal for a person's height. The weight excess or deficiency may, in part, be accounted for by body fat ( adipose tissue ) although other factors such as muscularity also affect BMI significantly (see discussion below and overweight ). The WHO regards an adult BMI of less than 18.5 as underweight and possibly indicative of malnutrition , an eating disorder , or other health problems, while
2318-506: A higher risk of type 2 diabetes mellitus and atherosclerotic cardiovascular disease at BMIs lower than the WHO cut-off point for overweight, 25 kg/m, although the cut-off for observed risk varies among different populations. The cut-off for observed risk varies based on populations and subpopulations in Europe, Asia and Africa. The Hospital Authority of Hong Kong recommends the use of
2440-418: A large (or tall) frame and underestimates roughly 10% for a smaller frame (short stature). In other words, people with small frames would be carrying more fat than optimal, but their BMI indicates that they are normal . Conversely, large framed (or tall) individuals may be quite healthy, with a fairly low body fat percentage , but be classified as overweight by BMI. For example, a height/weight chart may say
2562-477: A magnetic field to the body and measures the difference in relaxation rates of hydrogen atoms within fat versus lean mass. 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, and wildlife including birds. Assessment of somatic (skeletal) protein
SECTION 20
#17327901606302684-509: A means to prevent a further increase in BMI. In France, Italy, and Spain, legislation has been introduced banning the usage of fashion show models having a BMI below 18. In Israel, a model with BMI below 18.5 is banned. This is done to fight anorexia among models and people interested in fashion. A study published by Journal of the American Medical Association ( JAMA ) in 2005 showed that overweight people had
2806-420: A priori in the equivalence principle of general relativity . The International System of Units (SI) unit of mass is the kilogram (kg). The kilogram is 1000 grams (g), and was first defined in 1795 as the mass of one cubic decimetre of water at the melting point of ice. However, because precise measurement of a cubic decimetre of water at the specified temperature and pressure was difficult, in 1889
2928-407: A quantitative analysis of several studies, involving more than 600,000 men and women, the lowest mortality rates were found for people with BMIs between 23 and 29; most of the 25–30 range considered 'overweight' was not associated with higher risk. Mass Mass is an intrinsic property of a body . It was traditionally believed to be related to the quantity of matter in a body, until
3050-477: A statistical measurement for groups, the BMI has limitations that can make it less useful than some of the alternatives , especially when applied to individuals with abdominal obesity , short stature , or high muscle mass . BMIs under 20 and over 25 have been associated with higher all-cause mortality, with the risk increasing with distance from the 20–25 range. Adolphe Quetelet , a Belgian astronomer , mathematician, statistician , and sociologist , devised
3172-468: A string, does the combined system fall faster because it is now more massive, or does the lighter body in its slower fall hold back the heavier body? The only convincing resolution to this question is that all bodies must fall at the same rate. A later experiment was described in Galileo's Two New Sciences published in 1638. One of Galileo's fictional characters, Salviati, describes an experiment using
3294-410: A uniform acceleration and a uniform gravitational field. Thus, the theory postulates that the force acting on a massive object caused by a gravitational field is a result of the object's tendency to move in a straight line (in other words its inertia) and should therefore be a function of its inertial mass and the strength of the gravitational field. In theoretical physics , a mass generation mechanism
3416-460: A vacuum, as David Scott did on the surface of the Moon during Apollo 15 . A stronger version of the equivalence principle, known as the Einstein equivalence principle or the strong equivalence principle , lies at the heart of the general theory of relativity . Einstein's equivalence principle states that within sufficiently small regions of spacetime, it is impossible to distinguish between
3538-436: A vague means of estimating adiposity . The duality of the BMI is that, while it is easy to use as a general calculation, it is limited as to how accurate and pertinent the data obtained from it can be. Generally, the index is suitable for recognizing trends within sedentary or overweight individuals because there is a smaller margin of error. The BMI has been used by the WHO as the standard for recording obesity statistics since
3660-436: 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
3782-427: Is 22.4 for women and 23.6 for men. High BMI is associated with type 2 diabetes only in people with high serum gamma-glutamyl transpeptidase . In an analysis of 40 studies involving 250,000 people, patients with coronary artery disease with normal BMIs were at higher risk of death from cardiovascular disease than people whose BMIs put them in the overweight range (BMI 25–29.9). One study found that BMI had
Body mass index - Misplaced Pages Continue
3904-485: Is a balance scale , which balances the force of one object's weight against the force of another object's weight. The two sides of a balance scale are close enough that the objects experience similar gravitational fields. Hence, if they have similar masses then their weights will also be similar. This allows the scale, by comparing weights, to also compare masses. Consequently, historical weight standards were often defined in terms of amounts. The Romans, for example, used
4026-402: Is a direct application of Archimedes' principle, that an object displaces its own volume of water. 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
4148-421: 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. Another method to estimate body water
4270-486: Is a technique used for measuring body shape. Initially, BVI technology employed white light scanning machines to measure an individual's body shape. 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. Body composition can also be measured using
4392-450: Is a theory which attempts to explain the origin of mass from the most fundamental laws of physics . To date, a number of different models have been proposed which advocate different views of the origin of mass. The problem is complicated by the fact that the notion of mass is strongly related to the gravitational interaction but a theory of the latter has not been yet reconciled with the currently popular model of particle physics , known as
4514-419: Is adequate for most of classical mechanics, and sometimes remains in use in basic education, if the priority is to teach the difference between mass from weight.) This traditional "amount of matter" belief was contradicted by the fact that different atoms (and, later, different elementary particles) can have different masses, and was further contradicted by Einstein's theory of relativity (1905), which showed that
4636-423: Is calculated in the same way as for adults but then compared to typical values for other children or youth of the same age. Instead of comparison against fixed thresholds for underweight and overweight, the BMI is compared against the percentiles for children of the same sex and age. A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered obese. Children with
4758-487: Is expressed in kg/m, resulting from mass in kilograms and height in metres. If pounds and inches are used, a conversion factor of 703 (kg/m)/(lb/in) is applied. (If pounds and feet are used, a conversion factor of 4.88 is used.) When the term BMI is used informally, the units are usually omitted. BMI provides a simple numeric measure of a person's thickness or thinness , allowing health professionals to discuss weight problems more objectively with their patients. BMI
4880-411: Is not the most appropriate measure for the risk of heart attack, stroke or death. A better measure was found to be the waist-to-height ratio . A 2011 study that followed 60,000 participants for up to 13 years found that waist–hip ratio was a better predictor of ischaemic heart disease mortality. The medical establishment and statistical community have both highlighted the limitations of BMI. Part of
5002-422: Is often better calculated using measures of body fat, as determined by such techniques as skinfold measurements or underwater weighing and the limitations of manual measurement have also led to alternative methods to measure obesity, such as the body volume indicator . It is not clear where on the BMI scale the threshold for overweight and obese should be set. Because of this, the standards have varied over
Body mass index - Misplaced Pages Continue
5124-485: Is placed at a distance r (center of mass to center of mass) from a second body of mass m B , each body is subject to an attractive force F g = Gm A m B / r , where G = 6.67 × 10 N⋅kg ⋅m is the "universal gravitational constant ". This is sometimes referred to as gravitational mass. Repeated experiments since the 17th century have demonstrated that inertial and gravitational mass are identical; since 1915, this observation has been incorporated
5246-408: Is the acceleration due to Earth's gravitational field , (expressed as the acceleration experienced by a free-falling object). For other situations, such as when objects are subjected to mechanical accelerations from forces other than the resistance of a planetary surface, the weight force is proportional to the mass of an object multiplied by the total acceleration away from free fall, which is called
5368-430: Is the basis by which masses are determined by weighing . In simple spring scales , for example, the force F is proportional to the displacement of the spring beneath the weighing pan, as per Hooke's law , and the scales are calibrated to take g into account, allowing the mass M to be read off. Assuming the gravitational field is equivalent on both sides of the balance, a balance measures relative weight, giving
5490-427: Is the gravitational mass ( standard gravitational parameter ) of the body causing gravitational fields, and R is the radial coordinate (the distance between the centers of the two bodies). By finding the exact relationship between a body's gravitational mass and its gravitational field, Newton provided a second method for measuring gravitational mass. The mass of the Earth can be determined using Kepler's method (from
5612-410: Is theoretically possible to collect an immense number of small objects and form them into an enormous gravitating sphere. However, from a practical standpoint, the gravitational fields of small objects are extremely weak and difficult to measure. Newton's books on universal gravitation were published in the 1680s, but the first successful measurement of the Earth's mass in terms of traditional mass units,
5734-446: 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. Many methods of determining body composition use
5856-703: The Journal of Chronic Diseases by Ancel Keys and others. In this paper, Keys argued that what he termed the BMI was "if not fully satisfactory, at least as good as any other relative weight index as an indicator of relative obesity". The interest in an index that measures body fat came with observed increasing obesity in prosperous Western societies. Keys explicitly judged BMI as appropriate for population studies and inappropriate for individual evaluation. Nevertheless, due to its simplicity, it has come to be widely used for preliminary diagnoses. Additional metrics, such as waist circumference, can be more useful. The BMI
5978-472: The Brout–Englert–Higgs mechanism . There are several distinct phenomena that can be used to measure mass. Although some theorists have speculated that some of these phenomena could be independent of each other, current experiments have found no difference in results regardless of how it is measured: The mass of an object determines its acceleration in the presence of an applied force. The inertia and
6100-467: The Cavendish experiment , did not occur until 1797, over a hundred years later. Henry Cavendish found that the Earth's density was 5.448 ± 0.033 times that of water. As of 2009, the Earth's mass in kilograms is only known to around five digits of accuracy, whereas its gravitational mass is known to over nine significant figures. Given two objects A and B, of masses M A and M B , separated by
6222-622: The Ponderal index is based on the natural scaling of mass with the third power of the height. However, many taller people are not just "scaled up" short people but tend to have narrower frames in proportion to their height. Carl Lavie has written that "The B.M.I. tables are excellent for identifying obesity and body fat in large populations, but they are far less reliable for determining fatness in individuals." For US adults, exponent estimates range from 1.92 to 1.96 for males and from 1.45 to 1.95 for females. The BMI overestimates roughly 10% for
SECTION 50
#17327901606306344-543: The Solar System . On 25 August 1609, Galileo Galilei demonstrated his first telescope to a group of Venetian merchants, and in early January 1610, Galileo observed four dim objects near Jupiter, which he mistook for stars. However, after a few days of observation, Galileo realized that these "stars" were in fact orbiting Jupiter. These four objects (later named the Galilean moons in honor of their discoverer) were
6466-613: The Standard Model . The concept of amount is very old and predates recorded history . The concept of "weight" would incorporate "amount" and acquire a double meaning that was not clearly recognized as such. What we now know as mass was until the time of Newton called “weight.” ... A goldsmith believed that an ounce of gold was a quantity of gold. ... But the ancients believed that a beam balance also measured “heaviness” which they recognized through their muscular senses. ... Mass and its associated downward force were believed to be
6588-457: 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. 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
6710-405: The carob seed ( carat or siliqua ) as a measurement standard. If an object's weight was equivalent to 1728 carob seeds , then the object was said to weigh one Roman pound. If, on the other hand, the object's weight was equivalent to 144 carob seeds then the object was said to weigh one Roman ounce (uncia). The Roman pound and ounce were both defined in terms of different sized collections of
6832-416: The proper acceleration . Through such mechanisms, objects in elevators, vehicles, centrifuges, and the like, may experience weight forces many times those caused by resistance to the effects of gravity on objects, resulting from planetary surfaces. In such cases, the generalized equation for weight W of an object is related to its mass m by the equation W = – ma , where a is the proper acceleration of
6954-453: The torsion balance pendulum, in 1889. As of 2008 , no deviation from universality, and thus from Galilean equivalence, has ever been found, at least to the precision 10 . More precise experimental efforts are still being carried out. The universality of free-fall only applies to systems in which gravity is the only acting force. All other forces, especially friction and air resistance , must be absent or at least negligible. For example, if
7076-444: The "Galilean equivalence principle" or the " weak equivalence principle " has the most important consequence for freely falling objects. Suppose an object has inertial and gravitational masses m and M , respectively. If the only force acting on the object comes from a gravitational field g , the force on the object is: Given this force, the acceleration of the object can be determined by Newton's second law: Putting these together,
7198-555: The 1990s the World Health Organization (WHO) decided that a BMI of 25 to 30 should be considered overweight and a BMI over 30 is obese, the standards the NIH set. This became the definitive guide for determining if someone is overweight. One study found that the vast majority of people labelled 'overweight' and 'obese' according to current definitions do not in fact face any meaningful increased risk for early death. In
7320-502: 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). However, it is also common to use a DEXA scan alone and refer to this as the "gold standard". These claims are somewhat dubious since measurements methods vary significantly from study to study. In practice,
7442-457: The BMI will be mostly correct when determining a person to be obese, but can err quite frequently when determining a person not to be. Despite this undercounting of obesity by BMI, BMI values in the intermediate BMI range of 20–30 were found to be associated with a wide range of body fat percentages. For men with a BMI of 25, about 20% have a body fat percentage below 20% and about 10% have body fat percentage above 30%. Body composition for athletes
SECTION 60
#17327901606307564-506: The Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force. In the Standard Model of physics, the mass of elementary particles is believed to be a result of their coupling with the Higgs boson in what is known as
7686-727: The UK, NICE guidance recommends prevention of type 2 diabetes should start at a BMI of 30 in White and 27.5 in Black African , African-Caribbean , South Asian , and Chinese populations. Research since 2021 based on a large sample of almost 1.5 million people in England found that some ethnic groups would benefit from prevention at or above a BMI of (rounded): In 1998, the U.S. National Institutes of Health brought U.S. definitions in line with World Health Organization guidelines, lowering
7808-472: The United States' third National Health and Nutrition Examination Survey (NHANES III) and found that BMI-defined obesity (BMI ≥ 30) was present in 21% of men and 31% of women. Body fat-defined obesity was found in 50% of men and 62% of women. While BMI-defined obesity showed high specificity (95% for men and 99% for women), BMI showed poor sensitivity (36% for men and 49% for women). In other words,
7930-412: The accuracy of BIA machines. 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. The Body Volume Index (BVI)
8052-426: The advantage of being able to also directly measure muscle thickness and quantify intramuscular fat. In the abdomen, ultrasonography is a useful tool for quantifying both subcutaneous and visceral fat. 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. Quantitative magnetic resonance (QMR) applies
8174-478: The basis of the BMI between 1830 and 1850 as he developed what he called "social physics". Quetelet himself never intended for the index, then called the Quetelet Index, to be used as a means of medical assessment. Instead, it was a component of his study of l'homme moyen , or the average man. Quetelet thought of the average man as a social ideal, and developed the body mass index as a means of discovering
8296-401: The body. Common models include: 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,
8418-425: 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). Total body water may be effectively measured using isotope dilution analysis of deuterium oxide. Potassium 40
8540-405: The classical theory offers no compelling reason why the gravitational mass has to equal the inertial mass. That it does is merely an empirical fact. Albert Einstein developed his general theory of relativity starting with the assumption that the inertial and passive gravitational masses are the same. This is known as the equivalence principle . The particular equivalence often referred to as
8662-426: 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. The ideal percent of body mass which should be fat depends on an individual's sex, age, and physical activity. For example,
8784-406: The concept of mass . Every experiment to date has shown these seven values to be proportional , and in some cases equal, and this proportionality gives rise to the abstract concept of mass. There are a number of ways mass can be measured or operationally defined : In everyday usage, mass and " weight " are often used interchangeably. For instance, a person's weight may be stated as 75 kg. In
8906-493: The different components (or "compartments") of a human body . The selection of compartments varies by model but may include fat , bone , water , and muscle . 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. Body composition models typically use between 2 and 6 compartments to describe
9028-458: The discovery of the atom and particle physics . It was found that different atoms and different elementary particles , theoretically with the same amount of matter, have nonetheless different masses. Mass in modern physics has multiple definitions which are conceptually distinct, but physically equivalent. Mass can be experimentally defined as a measure of the body's inertia , meaning the resistance to acceleration (change of velocity ) when
9150-470: The double of the distance between the two bodies. Hooke urged Newton, who was a pioneer in the development of calculus , to work through the mathematical details of Keplerian orbits to determine if Hooke's hypothesis was correct. Newton's own investigations verified that Hooke was correct, but due to personal differences between the two men, Newton chose not to reveal this to Hooke. Isaac Newton kept quiet about his discoveries until 1684, at which time he told
9272-659: The early 1980s. This general correlation is particularly useful for consensus data regarding obesity or various other conditions because it can be used to build a semi-accurate representation from which a solution can be stipulated, or the RDA for a group can be calculated. Similarly, this is becoming more and more pertinent to the growth of children, since the majority of children are sedentary. Cross-sectional studies indicated that sedentary people can decrease BMI by becoming more physically active. Smaller effects are seen in prospective cohort studies which lend to support active mobility as
9394-473: The edge of small/medium or medium/large, common sense should be used in calculating one's ideal weight. However, falling into one's ideal weight range for height and build is still not as accurate in determining health risk factors as waist-to-height ratio and actual body fat percentage. Accurate frame size calculators use several measurements (wrist circumference, elbow width, neck circumference, and others) to determine what category an individual falls into for
9516-434: The elapsed time could be measured. The ball was allowed to roll a known distance down the ramp, and the time taken for the ball to move the known distance was measured. The time was measured using a water clock described as follows: Galileo found that for an object in free fall, the distance that the object has fallen is always proportional to the square of the elapsed time: Galileo had shown that objects in free fall under
9638-497: The exact number of carob seeds that would be required to produce a gravitational field similar to that of the Earth or Sun. In fact, by unit conversion it is a simple matter of abstraction to realize that any traditional mass unit can theoretically be used to measure gravitational mass. Measuring gravitational mass in terms of traditional mass units is simple in principle, but extremely difficult in practice. According to Newton's theory, all objects produce gravitational fields and it
9760-410: The feather should hit the ground at exactly the same time (assuming the acceleration of both objects towards each other, and of the ground towards both objects, for its own part, is negligible). This can easily be done in a high school laboratory by dropping the objects in transparent tubes that have the air removed with a vacuum pump. It is even more dramatic when done in an environment that naturally has
9882-404: The first celestial bodies observed to orbit something other than the Earth or Sun. Galileo continued to observe these moons over the next eighteen months, and by the middle of 1611, he had obtained remarkably accurate estimates for their periods. Sometime prior to 1638, Galileo turned his attention to the phenomenon of objects in free fall, attempting to characterize these motions. Galileo was not
10004-402: The first paragraph of Principia , Newton defined quantity of matter as “density and bulk conjunctly”, and mass as quantity of matter. The quantity of matter is the measure of the same, arising from its density and bulk conjunctly. ... It is this quantity that I mean hereafter everywhere under the name of body or mass. And the same is known by the weight of each body; for it is proportional to
10126-436: The first to investigate Earth's gravitational field, nor was he the first to accurately describe its fundamental characteristics. However, Galileo's reliance on scientific experimentation to establish physical principles would have a profound effect on future generations of scientists. It is unclear if these were just hypothetical experiments used to illustrate a concept, or if they were real experiments performed by Galileo, but
10248-773: The following BMI ranges: A 2000 study from the Japan Society for the Study of Obesity (JASSO) presents the following table of BMI categories: In Singapore, the BMI cut-off figures were revised in 2005 by the Health Promotion Board (HPB), motivated by studies showing that many Asian populations, including Singaporeans, have a higher proportion of body fat and increased risk for cardiovascular diseases and diabetes mellitus , compared with general BMI recommendations in other countries. The BMI cut-offs are presented with an emphasis on health risk rather than weight. In
10370-572: The gap between Galileo's gravitational acceleration and Kepler's elliptical orbits. It appeared in Newton's 1728 book A Treatise of the System of the World . According to Galileo's concept of gravitation, a dropped stone falls with constant acceleration down towards the Earth. However, Newton explains that when a stone is thrown horizontally (meaning sideways or perpendicular to Earth's gravity) it follows
10492-421: The gravitational acceleration is given by: This says that the ratio of gravitational to inertial mass of any object is equal to some constant K if and only if all objects fall at the same rate in a given gravitational field. This phenomenon is referred to as the "universality of free-fall". In addition, the constant K can be taken as 1 by defining our units appropriately. The first experiments demonstrating
10614-424: 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. A wide variety of body composition measurement methods exist. The gold standard measurement technique for
10736-438: The ideal weight (BMI 21.5) for a 1.78-metre-tall (5 ft 10 in) man is 68 kilograms (150 lb). But if that man has a slender build (small frame), he may be overweight at 68 kg or 150 lb and should reduce by 10% to roughly 61 kg or 135 lb (BMI 19.4). In the reverse, the man with a larger frame and more solid build should increase by 10%, to roughly 75 kg or 165 lb (BMI 23.7). If one teeters on
10858-407: The inertial mass describe this property of physical bodies at the qualitative and quantitative level respectively. According to Newton's second law of motion , if a body of fixed mass m is subjected to a single force F , its acceleration a is given by F / m . A body's mass also determines the degree to which it generates and is affected by a gravitational field . If a first body of mass m A
10980-629: The influence of the Earth's gravitational field have a constant acceleration, and Galileo's contemporary, Johannes Kepler, had shown that the planets follow elliptical paths under the influence of the Sun's gravitational mass. However, Galileo's free fall motions and Kepler's planetary motions remained distinct during Galileo's lifetime. According to K. M. Browne: "Kepler formed a [distinct] concept of mass ('amount of matter' ( copia materiae )), but called it 'weight' as did everyone at that time." Finally, in 1686, Newton gave this distinct concept its own name. In
11102-760: The kilogram and several other units came into effect on 20 May 2019, following a final vote by the CGPM in November 2018. The new definition uses only invariant quantities of nature: the speed of light , the caesium hyperfine frequency , the Planck constant and the elementary charge . Non-SI units accepted for use with SI units include: Outside the SI system, other units of mass include: In physical science , one may distinguish conceptually between at least seven different aspects of mass , or seven physical notions that involve
11224-529: The kilogram was redefined as the mass of a metal object, and thus became independent of the metre and the properties of water, this being a copper prototype of the grave in 1793, the platinum Kilogramme des Archives in 1799, and the platinum–iridium International Prototype of the Kilogram (IPK) in 1889. However, the mass of the IPK and its national copies have been found to drift over time. The re-definition of
11346-418: The measurable mass of an object increases when energy is added to it (for example, by increasing its temperature or forcing it near an object that electrically repels it.) This motivates a search for a different definition of mass that is more accurate than the traditional definition of "the amount of matter in an object". Body composition In physical fitness , body composition refers to quantifying
11468-573: The measurement methods used will be a tradeoff between cost, availability, and accuracy. 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. DEXA measurements are highly reproducible if
11590-558: The motion of bodies in an orbit"). Halley presented Newton's findings to the Royal Society of London, with a promise that a fuller presentation would follow. Newton later recorded his ideas in a three-book set, entitled Philosophiæ Naturalis Principia Mathematica (English: Mathematical Principles of Natural Philosophy ). The first was received by the Royal Society on 28 April 1685–86; the second on 2 March 1686–87; and
11712-403: The nearby gravitational field. No matter how strong the gravitational field, objects in free fall are weightless , though they still have mass. The force known as "weight" is proportional to mass and acceleration in all situations where the mass is accelerated away from free fall. For example, when a body is at rest in a gravitational field (rather than in free fall), it must be accelerated by
11834-647: The normal/overweight cut-off from a BMI of 27.8 (men) and 27.3 (women) to a BMI of 25. This had the effect of redefining approximately 25 million Americans, previously healthy , to overweight . This can partially explain the increase in the overweight diagnosis in the past 20 years, and the increase in sales of weight loss products during the same time. WHO also recommends lowering the normal/overweight threshold for southeast Asian body types to around BMI 23, and expects further revisions to emerge from clinical studies of different body types. A survey in 2007 showed 63% of Americans were then overweight or obese, with 26% in
11956-483: The obese category (a BMI of 30 or more). By 2014, 37.7% of adults in the United States were obese, 35.0% of men and 40.4% of women; class 3 obesity (BMI over 40) values were 7.7% for men and 9.9% for women. The U.S. National Health and Nutrition Examination Survey of 2015-2016 showed that 71.6% of American men and women had BMIs over 25. Obesity—a BMI of 30 or more—was found in 39.8% of the US adults. The BMI ranges are based on
12078-509: The object caused by all influences other than gravity. (Again, if gravity is the only influence, such as occurs when an object falls freely, its weight will be zero). Although inertial mass, passive gravitational mass and active gravitational mass are conceptually distinct, no experiment has ever unambiguously demonstrated any difference between them. In classical mechanics , Newton's third law implies that active and passive gravitational mass must always be identical (or at least proportional), but
12200-430: The object from going into free fall. By contrast, on the surface of the Moon, the same object still has a mass of 50 kilograms but weighs only 81.5 newtons, because only 81.5 newtons is required to keep this object from going into a free fall on the moon. Restated in mathematical terms, on the surface of the Earth, the weight W of an object is related to its mass m by W = mg , where g = 9.80665 m/s
12322-412: The orbit of Earth's Moon), or it can be determined by measuring the gravitational acceleration on the Earth's surface, and multiplying that by the square of the Earth's radius. The mass of the Earth is approximately three-millionths of the mass of the Sun. To date, no other accurate method for measuring gravitational mass has been discovered. Newton's cannonball was a thought experiment used to bridge
12444-478: The past few decades. Between 1980 and 2000 the U.S. Dietary Guidelines have defined overweight at a variety of levels ranging from a BMI of 24.9 to 27.1. In 1985 the National Institutes of Health (NIH) consensus conference recommended that overweight BMI be set at a BMI of 27.8 for men and 27.3 for women. In 1998, an NIH report concluded that a BMI over 25 is overweight and a BMI over 30 is obese. In
12566-409: The planets orbit the Sun. In Kepler's final planetary model, he described planetary orbits as following elliptical paths with the Sun at a focal point of the ellipse . Kepler discovered that the square of the orbital period of each planet is directly proportional to the cube of the semi-major axis of its orbit, or equivalently, that the ratio of these two values is constant for all planets in
12688-416: The relationship between body weight and disease and death. Overweight and obese individuals are at an increased risk for the following diseases: Among people who have never smoked, overweight/obesity is associated with 51% increase in mortality compared with people who have always been a normal weight. The BMI is generally used as a means of correlation between groups related by general mass and can serve as
12810-464: The relative gravitation mass of each object. Mass was traditionally believed to be a measure of the quantity of matter in a physical body, equal to the "amount of matter" in an object. For example, Barre´ de Saint-Venant argued in 1851 that every object contains a number of "points" (basically, interchangeable elementary particles), and that mass is proportional to the number of points the object contains. (In practice, this "amount of matter" definition
12932-554: The results obtained from these experiments were both realistic and compelling. A biography by Galileo's pupil Vincenzo Viviani stated that Galileo had dropped balls of the same material, but different masses, from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass. In support of this conclusion, Galileo had advanced the following theoretical argument: He asked if two bodies of different masses and different rates of fall are tied by
13054-458: The role of DEXA in clinical evaluations and research studies has been questioned by Wang et al. 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, 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
13176-433: The same body shape and relative composition have a larger BMI. BMI is proportional to the mass and inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high, compared to their actual body fat levels. In comparison,
13298-503: The same common mass standard, the carob seed. The ratio of a Roman ounce (144 carob seeds) to a Roman pound (1728 carob seeds) was: In 1600 AD, Johannes Kepler sought employment with Tycho Brahe , who had some of the most precise astronomical data available. Using Brahe's precise observations of the planet Mars, Kepler spent the next five years developing his own method for characterizing planetary motion. In 1609, Johannes Kepler published his three laws of planetary motion, explaining how
13420-407: The same thing. Humans, at some early era, realized that the weight of a collection of similar objects was directly proportional to the number of objects in the collection: where W is the weight of the collection of similar objects and n is the number of objects in the collection. Proportionality, by definition, implies that two values have a constant ratio : An early use of this relationship
13542-459: The same type of machine is used, 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,
13664-427: The scale is often biased. As noted by sociologist Sabrina Strings, the BMI is largely inaccurate for black people especially, disproportionately labelling them as overweight even for healthy individuals. The exponent in the denominator of the formula for BMI is arbitrary. The BMI depends upon weight and the square of height. Since mass increases to the third power of linear dimensions, taller individuals with exactly
13786-549: The skin fold test, which is performed using a measuring caliper . It can be done in nine steps: 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 has also been used to measure subcutaneous fat thickness, and by using multiple points an estimation of body composition can be made. Ultrasound has
13908-542: The socially ideal human person. According to Lars Grue and Arvid Heiberg in the Scandinavian Journal of Disability Research, Quetelet's idealization of the average man would be elaborated upon by Francis Galton a decade later in the development of Eugenics . The modern term "body mass index" (BMI) for the ratio of human body weight to squared height was coined in a paper published in the July 1972 edition of
14030-441: The square of the distance to the body's center. For example, according to Newton's theory of universal gravitation, each carob seed produces a gravitational field. Therefore, if one were to gather an immense number of carob seeds and form them into an enormous sphere, then the gravitational field of the sphere would be proportional to the number of carob seeds in the sphere. Hence, it should be theoretically possible to determine
14152-473: The statistical limitations of the BMI scale is the result of Quetelet's original sampling methods. As noted in his primary work, A Treatise on Man and the Development of His Faculties, the data from which Quetelet derived his formula was taken mostly from Scottish Highland soldiers and French Gendarmerie . The BMI was always designed as a metric for European men. For women, and people of non-European origin,
14274-500: The third on 6 April 1686–87. The Royal Society published Newton's entire collection at their own expense in May 1686–87. Isaac Newton had bridged the gap between Kepler's gravitational mass and Galileo's gravitational acceleration, resulting in the discovery of the following relationship which governed both of these: where g is the apparent acceleration of a body as it passes through a region of space where gravitational fields exist, μ
14396-492: The top of a high mountain" with sufficient velocity, "it would reach at last quite beyond the circumference of the Earth, and return to the mountain from which it was projected." In contrast to earlier theories (e.g. celestial spheres ) which stated that the heavens were made of entirely different material, Newton's theory of mass was groundbreaking partly because it introduced universal gravitational mass : every object has gravitational mass, and therefore, every object generates
14518-459: The universality of free-fall were—according to scientific 'folklore'—conducted by Galileo obtained by dropping objects from the Leaning Tower of Pisa . This is most likely apocryphal: he is more likely to have performed his experiments with balls rolling down nearly frictionless inclined planes to slow the motion and increase the timing accuracy. Increasingly precise experiments have been performed, such as those performed by Loránd Eötvös , using
14640-535: The weight. Robert Hooke had published his concept of gravitational forces in 1674, stating that all celestial bodies have an attraction or gravitating power towards their own centers, and also attract all the other celestial bodies that are within the sphere of their activity. He further stated that gravitational attraction increases by how much nearer the body wrought upon is to its own center. In correspondence with Isaac Newton from 1679 and 1680, Hooke conjectured that gravitational forces might decrease according to
14762-404: 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. Recent advancements such as 8-point electrodes, multi-frequency measurements, and Direct Segmental Analysis, have improved
14884-425: Was designed to be used as a simple means of classifying average sedentary (physically inactive) populations, with an average body composition . For such individuals, the BMI value recommendations as of 2014 are as follows: 18.5 to 24.9 kg/m may indicate optimal weight, lower than 18.5 may indicate underweight , 25 to 29.9 may indicate overweight , and 30 or more may indicate obese . Lean male athletes often have
#629370