Body mass

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Body mass


The body mass, M, is the mass (kilogram [kg]) of an individual (object) [x] and is expressed in units [kg/x]. Whereas the body weight changes as a function of gravitational force (you are weightless at zero gravity; your floating weight in water is different from your weight in air), your mass is independent of gravitational force, and it is the same in air and water.

Abbreviation: m [kg]; M [kg·x-1]

Reference: BEC 2020.1, Gnaiger 2019 MiP2019

Healthy reference population     Body mass excess         BFE         BME cutoffs         BMI         H         M         VO2max         mitObesity drugs

Communicated by Gnaiger Erich (2020-02-15) last update 2020-07-05
in: Stave XXX XXX-mass Carol on BME and mitObesity of A X-mass Carol

Body mass and body tissue mass versus mass of a tissue sample

  1. M [kg/x]: The SI unit for mass (of a system), m, is [kg] (1 kg = 1000 g). The body mass, M, is the mass, m [kg], per individual. The individual (object X=Body, abbreviated as X=B) is the unit-entity UX = UB. The unit-entity is the count NX of a singual object, NX=1 [x]. The individual (object) UB is a countable quantity. The number of individual objects is the quantity count NX, with the unit [x] as the elementary unit for the number of unit-entities. Accepting to write the unit [x] for the countable number of objects X explicitly, then the unit of M = m/NX is [kg/x]. The average body mass M in a population can be obtained theoretically in two ways: (1) M can be measured for each individual of a large sample and expressed as the average of N measurements. (2) The total mass, m [kg], of NX [x] individual objects can be obtained in a single measurement, and the average body mass per individual is then calculated as M = m/NX [kg/x]. Of course, the second approach is not practical for humans, but is typical for cultured cells or small animals, such as nematodes. It is suggested to use the upper case letter M as the symbol for the quantity mass per object. The term elementary mass may be considered for the mass per unit-entity.
  2. M versus m: The SI symbol m is used to indicate the mass of a system or sample [kg], whereas the symbol M is used to indicate the mass per individual (object) [kg·x-1]. A system is not a countable quantity and thus is not a number. Both, body mass, M [kg/x], and mass of a sample, m [kg], are extensive quantities, which depend on the size of the individual or the sample. The mass of a tissue (e.g., muscle or fat) is of interest in two contexts: (1) The tissue (muscle, M) mass obtained from a biopsy, mM [kg] or [mg] of wet or dry tissue mass; and (2) the total muscle or fat mass per individual object, MM or MF [kg/x]. The extensive quantity m is frequently confused with the quantity weight, which is a force. The term 'body weight' is common, due to the practical sensory experience of heavy or light things. The terms 'massive' and 'heavy' may not be well discerned in practical language, since mass is a rather abstract concept and practically felt as a weight (see Canon X: Taking part in an X-mass party).

Human body mass

The elementary body mass of a human is measured without outdoor clothing (in light underware or swimsiut and without shoes) standing upright on a firm horizontally leveled and calibrated balance. This SOP applies to mobile persons who can stand steadily for the measurement. Some studies apply rigorous standards: 'All measurements were done at least 3 h after a meal (including drink), and subjects were requested to refrain from strenuous exercise 12 h prior to the measurements. Subjects were asked to empty their bladder before the measurements. Females were not measured during their menstrual period' (Deurenberg 2001 Eur J Clin Nutr).
The total body mass is the sum of lean body mass and fat mass, M = ML + MF, or the sum of the reference body mass of an individual at a given height in the healthy reference population and excess body mass, M = M° + ME. The excess body mass, in turn, is the sum of excess lean and fat mass, ME = MLE + MFE. The body mass excess, BME, is normalized for the reference body mass, BME = M/M°.

Self-reported measurements

'Men overestimated their height by 1.3 to 1.9 cm and the women by 0.5 to 1.3 cm. Men overestimated their weight by up to 0.45 kg and women underestimated their weight by up to 1.4 kg' (Tipton 2012 Nursing).


Bioblast linkReferenceYear
Gnaiger Erich (2020) A X-mass Carol. Body Mass Excess and mitObesity. MitoFit Preprint Arch 2020.4.v0.
Gnaiger Erich et al ― MitoEAGLE Task Group (2020) Mitochondrial physiology. Bioenerg Commun 2020.1. doi:10.26124/bec:2020-0001.v1.2020
Erich Gnaiger
OXPHOS capacity in human muscle tissue and body mass excess – the MitoEAGLE mission towards an integrative database (Version 6; 2020-01-12).

MitoPedia: BME and mitObesity

» Body mass excess and mitObesity | BME and mitObesity news | Summary |

BME cutoff pointsBME cutoffObesity is defined as a disease associated with an excess of body fat with respect to a healthy reference condition. Cutoff points for body mass excess, BME cutoff points, define the critical values for underweight (-0.1 and -0.2), overweight (0.2), and various degrees of obesity (0.4, 0.6, 0.8, and above). BME cutoffs are calibrated by crossover-points of BME with established BMI cutoffs.
Body fat excessBFEIn the healthy reference population (HRP), there is zero body fat excess, BFE, and the fraction of excess body fat in the HRP is expressed - by definition - relative to the reference body mass, M°, at any given height. Importantly, body fat excess, BFE, and body mass excess, BME, are linearly related, which is not the case for the body mass index, BMI.
Body massm [kg]; M [kg·x-1]The body mass, M, is the mass (kilogram [kg]) of an individual (object) [x] and is expressed in units [kg/x]. Whereas the body weight changes as a function of gravitational force (you are weightless at zero gravity; your floating weight in water is different from your weight in air), your mass is independent of gravitational force, and it is the same in air and water.
Body mass excessBMEThe body mass excess, BME, is an index of obesity and as such BME is a lifestyle metric. The BME is a measure of the extent to which your actual body mass, M [kg/x], deviates from M° [kg/x], which is the reference body mass [kg] per individual [x] without excess body fat in the healthy reference population, HRP. A balanced BME is BME° = 0.0 with a band width of -0.1 towards underweight and +0.2 towards overweight. The BME is linearly related to the body fat excess.
Body mass indexBMIThe body mass index, BMI, is the ratio of body mass to height squared (BMI=M·H-2), recommended by the WHO as a general indicator of underweight (BMI<18.5 kg·m-2), overweight (BMI>25 kg·m-2) and obesity (BMI>30 kg·m-2). Keys et al (1972; see 2014) emphasized that 'the prime criterion must be the relative independence of the index from height'. It is exactly the dependence of the BMI on height - from children to adults, women to men, Caucasians to Asians -, which requires adjustments of BMI-cutoff points. This deficiency is resolved by the body mass excess relative to the healthy reference population.
ComorbidityComorbidities are common in obesogenic lifestyle-induced early aging. These are preventable, non-communicable diseases with strong associations to obesity. In many studies, cause and effect in the sequence of onset of comorbidities remain elusive. Chronic degenerative diseases are commonly obesity-induced. The search for the link between obesity and the etiology of diverse preventable diseases lead to the hypothesis, that mitochondrial dysfunction is the common mechanism, summarized in the term 'mitObesity'.
Healthy reference populationHRPA healthy reference population, HRP, establishes the baseline for the relation between body mass and height in healthy people of zero underweight or overweight, providing a reference for evaluation of deviations towards underweight or overweight and obesity. The WHO Child Growth Standards (WHO-CGS) on height and body mass refer to healthy girls and boys from Brazil, Ghana, India, Norway, Oman and the USA. The Committee on Biological Handbooks compiled data on height and body mass of healthy males from infancy to old age (USA), published before emergence of the fast-food and soft-drink epidemic. Four allometric phases are distinguished with distinct allometric exponents. At heights above 1.26 m/x the allometric exponent is 2.9, equal in women and men, and significantly different from the exponent of 2.0 implicated in the body mass index, BMI [kg/m2].
Height of humansh [m]; H [m·x-1]The height of humans, h, is given in SI units in meters [m]. Humans are countable objects, and the symbol and unit of the number of objects is N [x]. The average height of N objects is, H = h/N [m/x], where h is the heights of all N objects measured on top of each other. Therefore, the height per human has the unit [m·x-1] (compare body mass [kg·x-1]). Without further identifyer, H is considered as the standing height of a human, measured without shoes, hair ornaments and heavy outer garments.
Lengthl [m]Length l is an SI base quantity with SI base unit meter m. Quantities derived from length are area A [m2] and volume V [m3]. Length is an extensive quantity, increasing additively with the number of objects. The term 'height' h is used for length in cases of vertical position (see height of humans). Length of height per object, LUX [m·x-1] is length per unit-entity UX, in contrast to lentgth of a system, which may contain one or many entities, such as the length of a pipeline assembled from a number NX of individual pipes. Length is a quantity linked to direct sensory, practical experience, as reflected in terms related to length: long/short (height: tall/small). Terms such as 'long/short distance' are then used by analogy in the context of the more abstract quantity time (long/short duration).
MitObesity drugsBioactive mitObesity compounds are drugs and nutraceuticals with more or less reproducible beneficial effects in the treatment of diverse preventable degenerative diseases implicated in comorbidities linked to obesity, characterized by common mechanisms of action targeting mitochondria.
ObesityObesity is a disease resulting from excessive accumulation of body fat. In common obesity (non-syndromic obesity) excessive body fat is due to an obesogenic lifestyle with lack of physical exercise ('couch') and caloric surplus of food consumption ('potato'), causing several comorbidities which are characterized as preventable non-communicable diseases. Persistent body fat excess associated with deficits of physical activity induces a weight-lifting effect on increasing muscle mass with decreasing mitochondrial capacity. Body fat excess, therefore, correlates with body mass excess up to a critical stage of obesogenic lifestyle-induced sarcopenia, when loss of muscle mass results in further deterioration of physical performance particularly at older age.
VO2maxVO2max; VO2max/MMaximum oxygen consumption, VO2max, is and index of cardiorespiratory fitness, measured by spiroergometry on human and animal organisms capable of controlled physical exercise performance on a treadmill or cycle ergometer. VO2max is the maximum respiration of an organism, expressed as the volume of O2 at STPD consumed per unit of time per individual object [mL.min-1.x-1]. If normalized per body mass of the individual object, M [kg.x-1], mass specific maximum oxygen consumption, VO2max/M, is expressed in units [].

SI base units

Quantity Symbol for quantity Q Symbol for dimension Name of SI unit Symbol for SI unit uQ [*]
length l L meter m
mass m M kilogram kg
time t T second s
electric current I I ampere A
thermodynamic temperature T Θ kelvin K
amount of substance *,§ nX = NX·NA-1 N mole mol
count *,$ NX X elementary unit x
unit-entity *,$ UX U elementary unit x
charge *,€ QX = NX·zX·e I·T coulomb C = A·s
luminous intensity Iv J candela cd
[*] »SI base units, except for the canonical 'elementary unit' [x]. The following footnotes are canonical comments.
* For the quantities n, N, U, and Q, the entity-type X of the unit-entity U has to be specified in the text and indicated by a subscript: nO2; Nce; QX.
§ Amount nX is an elementary quantity, converting the elementary unit [x] into moles [mol] using the Avogadro constant, NA.
$ Count NX equals the number of unit-entities UX. In the SI, the quantity 'count' is explicitly considered as an exception: "Each of the seven base quantities used in the SI is regarded as having its own dimension. .. All other quantities, with the exception of counts, are derived quantities" (Bureau International des Poids et Mesures 2019 The International System of Units (SI)). A unit-entity UX is not a count (UX is not a number of UX). NX has the dimension X of a count and UX has the dimension U of a unit-entity, and both quantities have the same unit, the 'elementary unit' [x].
Charge is a derived SI quantity. Charge is an elementary quantity, converting the elementary unit [x] into coulombs [C] using the elementary charge, e, or converting moles [mol] into coulombs [C] using the Faraday constant, F. zX is the charge number of entity X, which is a constant for any defined entity X. QX = nX·zX·F


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Entity, count, and number, and SI base quantities / SI base units
Quantity name Symbol Unit name Symbol Comment
unit-entity UX counting-unit [x] UX, UB; [x] not in SI
count NX counting-unit [x] NX, NB; [x] not in SI
number N - dimensionless = NX·UX-1
amount of substance nB mole [mol] nX, nB
electric current I ampere [A] A = C·s-1
time t second [s]
length l meter [m] SI: metre
mass m kilogram [kg]
thermodynamic temperature T kelvin [K]
luminous intensity IV candela [cd]
Fundamental relationships
» Avogadro constant
» Boltzmann constant
» elementary charge
» Faraday constant
» gas constant
SI and related concepts
» International System of Units
» International Union of Pure and Applied Chemistry, IUPAC
» entity
» quantity
» dimension
» format
» motive unit


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