Little manual of auxology

If you are interested in these issues, you may also try our new book: Hermanussen, M (ed) Studying Human Growth and Development. Schweizerbart Science Publishers, Stuttgart. 2013.

Acceleration: the rate of change in velocity over time. In the auxological literature, the term is often synonymously used with secular trend.  Both terms must be used with caution as they are ambiguous. Some authors may not only refer to developmental tempo, but also to the amplitude of long-term secular trends in body height. 

Acceleration curves plot the slope of the growth velocity curves.

Accuracy and inaccuracy denote systematic bias, and may be due to instrument error, or to errors of measurement technique. Accuracy is the extent to which the ''true'' value of a measurement is attained, while inaccuracy is systematic bias which reduces the likelihood of attaining the true value.

Adequate Intake (AI) is the recommended average daily intake level based on observed or experimentally determined approximations or estimates of nutrient intake by a group (or groups) of apparently healthy people. AI is an assumption and it is used when an RDA cannot be determined.

Adiposity rebound refers to the second rise in skinfold thickness and BMI which usually occurs at about six years. The earlier the rebound, the higher the adiposity at adult age.

Adult height, also called final height is usually reached in the 3rd decade of life.

AGA (Adequate for Gestational Age) indicates birth weight between the 10th and the 90th centile, in contrast to SGA and LGA.

Allometry: Living organisms tend to exhibit differential growth rates in the various parts of their body, i.e. changes in overall body size are usually accompanied by disproportionate changes in the single parts. Allometry expresses the proportionality as a power law.
y = kx^a or in a logarithmic form: log y = a log x + log k
a is the scaling component
Allometry leads to the transformation of a material form into another material form (see chapter: Geometry and auxology). A simple way of transformation is the cartesian transformation.

Amplitude of growth refers to the increase of size, and can never be evaluated on its own, but always in view of the developmental tempo. A tall child may be high in amplitude, or fast in developmental tempo, or both.

Anogenital ratio (the distance: anus to fourchette, to anus to base of the clitoris) serves as a measure of foetal virilization in premature and full-term newborn infants. A ratio > 0.50 suggests labioscrotal fusion.

Anthropometry: greek άνθρωπος man, and μέτρον measure) AnthropometronAnthropometronrefers to measurements of the human body. The earliest device ever published for measuring body stature was described in 1654 by Johann Sigismund Elsholtz (Figure). It illustrates the measuring device with a movable board (regula) above the head, and the basis to stand on.

APHV (Age at Peak Height Velocity) is often used as a proxy for develompental tempo. In modern Western societies, APHV usully occurs around the age of 14 years in boys and 12 years in girls. In the mid-19th century, APHV in European children was approximately 2 years later.

Apple (android) type of fat distribution with high values of visceral fat is more often found in men; the female fat distribution pattern rather resembles a pear (gynoid type).

Arm span is an approximate surrogate for height (span = height ± 3.5 cm) in the patient unable to stand or with severe spinal deformity. It may be a useful measurement in children with dysproportionate stature, but valid references for arm span are rare.

Athletic refers to the visual impression of intermediate persons with high percentage of muscles in the body shape typology of Kretschmer, in contrast to leptosom (asthenic) and pyknosom. The athletic type nearly corresponds to metromorph or mesomorph individuals of other typologies.

Auxology (greek αυξω - I let grow): the science of somatic growth and development. Though auxology traditionally focuses on childhood and adolescence, growth and physical development remain an issue throughout the total life span of man.

Bioelectrical Impedance Analysis (BIA) determines the electrical impedance of the human body. The electrical impedance reflects total body water content of the body.

Biological age, in contrast to chronological or calendar age refers to the state of maturation or the degree of physiological development of a human organism. The tempo at which the biological age of an individual proceeds can differ from the tempo of the calendar age; it depends on sex, on genetics, ethnicity, type of body shape, and environmental factors.

Body Mass Index (BMI) describes a relation between body weight and stature. We calculate: BMI = body weight / stature². Adults with BMI greater than 30 kg/m² are considered obese, adults with BMI between 25 and 30 kg/m² are considered overweight, age specific tables with reference data exist for children and adolescents.

Body surface area (BSA) is often used as an indicator of metabolic mass instead of the body weight. BSA is less affected by the amount of adipose tissue. Various formulas have been published; the DuBois formula published in 1916 still belongs to the most widely used formulas (see chapter: Normogram for body surface area).

Canalisation of growth refers to the tracking of individual height gain within a limited number of restricted pathways, also named growth channels.

Catch-up growth is a physiological condition of temporary overgrowth. It is characterized by an increase in centile position and thus requires that height velocity exceeds the statistical limits of normality for age and/or maturity during a defined period of time, following a transient period of growth inhibition. It may not be mistaken for rapid growth, an abnormal condition of overgrowth.

Centile (or percentile): the value of a variable below which a given percent of the observations can be found. E.g. 25 percent of the observations can be found below the 25th centile. The 25th centile is also known as the first quartile (Q1). Some people prefer the term percentile, probably because that is what Francis Galton called them in 1875 when he invented them. But the other quantiles like quartiles, quintiles, deciles etc do not start with the prefix per. The term centile is preferred (Tim Cole).

First and 99th centile are important cut-offs for safety; third and 97the centile are often used as critical cut-offs for health issues; fifth and 95th centile are important in ergonomics; tenth and 90th centile are often used to describe cut-offs in weight.

Centile often pretend a precision that does not exist. Similar to mean values that are afflicted with a technical error of the mean, also centiles are afflicted with imprecision. The precision of a centile depends on various factors, particularly on the number of subjects that were used to construct the centile. Precise evaluation of the outer centiles (3rd and 97th, 1st and 99th) requires large numbers of observations, a requirement that is often not fulfilled. Growth references tend to ignore this problem. Confidence intervals for centiles are usually not published.

Chronological or calendar age, in contrast to biological  age, refers to the physical time scale of maturation and ageing.

Coefficient of variation is the standard deviation measure divided by the mean.

Coefficient of reliability (R) is R = 1 - ((total TEM)²/SD²). SD² is the variance of the study including measurement error. In the case of an R of 0.95, 95% of the variance is due to factors other than measurement error.

Community effects refer to the social networks that significantly shape human behaviour. Recent evidence suggests that social interactions may also interfere with the regulation of growth in the sense that the community sets the target for growth and final height in healthy adolescents.

Conditional target height (cTH) is expressed in SD scores: cTH SDS = (fatherSDS + motherSDS)/2 * 0.72

Conditional target height SDS equals mean parental height SDS, multiplied by the factor 0.72.

Confidence intervals (CI) indicate the reliabilty of an estimate. The CI alludes to the fact that observations differ from sample to sample, if an experiment is frequently repeated.

Constitutional delay of growth and development (CDGD) refers to a slower pace, i.e. a delay in developmental tempo in otherwise healthy children and adolescents. They are often short and enter puberty late. There is also a constitutional acceleration of growth and development referring to accelerated developmental tempo. These individuals are usually tall and mature early. There may be a familial predisposition to tempo variation.

Cope's rule (Edward Drinker Cope 1840 – 1897) described the evolutionary trend towards larger body size that is usually found among mammals. The trend is also observed in certain organs, or parts of their bodies (teeth, horns, trunks etc). It is common belief that large size improves thermal efficiency and evolutionary success. Yet, this explanation may be questioned. The trend may be an automatics as there is little evidence of a reversal when the somatic enlargements no longer appear favorable in the evolutionary context (e.g. in several extinct species such as saber-tooth cats, Irish elks etc). Yet, there is evidence of an island effect where there is reduced body size for populations on islands with limited resources (e.g. mammoth, deer).

CpG islands or CG islands are genomic regions with a high frequency of CpG sites. C and G are connected by a phosphodiester bond (p), and are situated on the same strand of DNA or RNA. The cytosin of the CpG dinucleotide is the main target for DNA methylation. Cytosine methylation often occurs close to transcription start sites of genes and can persist via the parental germ line into the next generation (genetic imprinting). CpG island are important prerequisites for epigenetic modifications.

Cross-sectional - in contrast to longitudinal studies - consist of measurements that were obtained within a short period of time. Cross-sectional studies permit an instantaneous impression on growth and development, but they must be looked upon with great care when deriving information on growth velocity.

Development denotes a gradual process of serial progressive, often canalized unfolding usually accompanied by somatic growth passaging from the lower state of organization to maturity. Please note that the term developmental tempo is an auxiliary construct. The tempo of physical growth and development in fact, may grossly differ from the progress in mental, emotional or other aspects of child and adolescent maturation.

Developmental Origins of Health and Disease (DOHaD) hypothesis deals with an individual's memory of exposure to inappropriate environments in early life, e.g. by epigenetic modification, that potentially leads to disease in later life.

Developmental tempo denotes the tempo, or the velocity at which a child matures, differs between the children. Some adolescents though aged 12 years, still look like 10 years old ones, they are as tall as their 10 year old mates, and still wait for their pubertal development; other 12 year old ones almost look adult, and among other signs are also sexually more mature than their age mates.

Aspect and biological maturity often differ from psychological and school development, but biological maturity usually correlates with growth and bone maturation. Children who mature at slow pace, usually also show a delayed bone age (or skeletal age), they are called constitutionally delayed. Children who mature at fast pace in whom bone age is more advanced than chronological age are called constitutionally advanced.

DEXA  (Dual Energy X-Ray Absorptiometry) uses two X-ray energies to measure body fat, muscle, and bone mineral. A person lays in the supine position on an X-ray table. Based on the three component model of body composition, the results are whole body and regional estimates of fat, muscle, and bone mineral. There is concern about radiation exposure so this is not a screening technique.

Disorders of sex development (DSD) as defined by the Consensus Statement on Management of Intersex Disorders, are congenital conditions in which development of chromosomal, gonadal, or anatomical sex is atypical. The term DSD is recommended to replace potentially confusing and stigmatizing terms such as intersex, pseudohermaphroditism, hermaphroditism, and sex reversal, as well as gender-based diagnostic labels such as male/female pseudohermaphroditism.

Distance charts provide centiles for height, weight and other anthropometric parameters against age. The term was coined to pinpoint the difference between charts that depict height and charts that depict height changes over time (velocity charts).

Dwarfism is a disrespectful term for extreme short stature and should be avoided. In medical history it referred to adult body height below 120 cm, some authors talked about adult height below 130 cm.

Epiphyseal growth plates consist of a small cartilaginous disc between diaphysis (the long part of a long bone) and epiphysis (the distal part of a long bone). Long bones usually have two Epiphyseal growth plates. These plates are well organized, cartilage celles are not only closely packed, but show a distinct "column-like" appearance. This characteristic feature is necessary for the direction of growth. EpihysenfugeEpihysenfuge

The Figure shows a thigh bone (left), and a small enlarged section (center). There is an obvious column-like structrue of the cells (schematic view at the right side).

Epiphyseal growth plates become smaller during childhood and adolescence and finally ossify in a strictly regulated sequence during puberty or a little later. When the plates have fused – usually after puberty – and when they are completely ossified longitudinal bone growth stops. Not all growth plates mature at the same speed. Therefore - particularly during puberty - body proportions change.


Failure to thrive/growth faltering: Poor weight gain in infants and toddlers with a fall across 2 or more centile lines. The definition is widely used, but may be misleading in early infancy. Particularly during the first year of life, infants tend to '''find their later growth canal''' while crossing several centiles without apparent nutritional or health related reasons.

Fat mass (FM) denotes all extractable lipids of the body, from adipose and non-adipose tissues.

Fat free mass (FFM) denotes all lipid free material of the body such as water, bone, connective tissues, muscles and internal organs.

Final height, also called adult height is usually reached in the 3rd decade of life.

Frame Index was introduced by Frisancho as a measure of skeletal robusticity and relates elbow breadth, height and age

Frame Index = [elbow breadth (mm)/stature (cm)]*100

Frankfurt Horizontal Plane (Frankfurter Ebene) is a virtual plane that cuts through the lowest point of the bony orbitae and the tragions. It is used for reasons of comparability to keep the head in a defined position while measuring stature.

GigantGigantGigantism: We talk about true gigantism when body height surpasses 7 1/2 feet, i.e. 229 cm, other authors talk about 8 feet, i.e. 244 cm.

This size is very rare, and can only be achieved during long periods of excessively elevated growth hormone production during childhood. Elevated growth hormone production in adults results in acromegalie. Acromegalie is much more common and may be regarded the adult form of gigantism. After most epiphyseal growth plates have fused, longitudinal growth is terminated. Only the tips of the fingers, the nose, the acra may go on growing. Acromegalic patients have a typical coarse face.

Grandmothering refers to the evolutionary advantage of grandmother's help to her daughter's and her daughter-in-law's progeny.

Growing pains are common in healthy children. They are typically located in the legs, usually close to the tibial tuberosity and characteristically occur at night, and are felt on both sides. Though they are not considered an illness, they may substantially effect well being. The cause of growing pains is not known. Yet, short term peak height velocities of more than 100µm per hour in the lower leg could be responsible for this phenomenon.

Growth is that kind of change of an organic system that can be monitored by measurable changes in length or weight.

Growth channels refer to the limited number of restricted pathways within which individual height gain occurs.

Growth charts are graphic designs and illustrate growth references as a visual display.

Growth potential of a child is defined as final height (h) minus current height (H) divided by final height (growth potential = (H − h)/H), and suggests that we can predict growth from the state of maturation alone. The idea is intriguing but in deed too simplistic. The remaining growth of a child is influenced by more factors than just by bone age and pubertal stage.

Growth references are statistical summaries of anthropometry, conditioned (usually) on age and sex. References describe how children do grow, in contrast to growth standards that describe how children should grow.

Growth spurts (periodic or sporadic temporary increments in growth velocity) are ubiquiteous phenomena in growth, and are traditionally looked upon as spurts in amplitude. Yet, considering the complementary concept of amplitude and tempo in growth, growth spurts may also be looked upon as spurts in tempo, i.e. as temporary changes in the progress of biological ageing.

Growth tracks: SDS patternsSDS patternsChildren of the same age are not equal in stature. Body height varies around mean height and can be expressed as SDS (standard deviation score). This means, body height can be expressed relative to mean height. 95 percent of all height measures vary between minus two and plus two height-SDS. The remaining children are taller or shorter, i.e. their body height differs by more than 2 SDS from mean height. Children grow and become taller in terms of centimetres, but they can remain on the same height-SDS for many years. Some children grow faster than others, they change height-SDS. Growth tracks are patterns of height-SDS. Children who grow at average velocity persist on their former height SDS, they grow horizontally and have horizontal growth tracks. Children who grow slower than their peers, show declining growth tracks. Children who grow faster than their peers, show increasing growth tracks. The idea of growth tracks replaces the traditional ideas of growth as a strictly "canalized" process. The graph illustrates three height SDS patterns of girls. The upper girl grows at average tempo, the second girl - late maturing - at retarded and the third girl - early maturing - at accelerated tempo. Mid-puberty (the moment of peak height velocity) is indicated by the vertical line. Average tempo of growth is characterized by horizontal patterns, retarded tempo by a downward SDS peak (usually before the age at peak height velocity), accelerated tempo by an upward peak (usually after the age at peak height velocity).

Growth tracking indicates that individuals do not exhibit unlimited variation in growth, but tend to track along a limited number of restricted pathways (growth trajectories). The concept of growth tracking within one or two growth channels is also called canalisation.

Growth trajectories belong to the concept of growth tracking, and indicate those tracks that individuals are supposed to grow along between birth and maturity.

Growth velocity is the rate at which height, weight, and other parameters change over time. Growth velocity is defined by calendar time and does not refer to developmental tempo. Growth velocity is the difference between two measurements (of height, weight etc.) divided by the time interval between them, and is usually given as an annual rate of increment.

Height age is an age defined by height. Taller children tend to be older. The term was common among paediatricians for many decades, but it is misleading and should be abandoned.

Harris linesHarris linesHarris Linien are transverse, horizontally disposed formations of interlacing trabeculae, viewed in X-rays of long bones parallel to the epiphyseal growth plates. Harris Lines are traditionally viewed as an expression of previous disturbances in longitudinal bone growth. Recent evidence however, suggests that Harris lines may also occur during physiological bone growth.

Many Bronze age people suffered from early spring starvation in Northern Europe. Also their children starved, and probably also suffered from periodical growth arrests. The picture illustrates X-rays of bone fragments of people who died as adolescents and were burned and buried in urnes. Still, Harris Lines can be observed, occuring at annual rings similar to trees. We believe that these lines occured during and after early spring starvation. 

Height prediction. There are three approaches to predict final height. The parental approach - the idea: height of the child is related to parent and population height, the child will find his/her target height; the canalisation approach - the idea: children tend to track in growth along a limited number of restricted growth canals; and the the '''maturity approach''' - the idea: the current state of maturity, the biological age as assessed by X-ray imaging of hand and wrist, is used as an indicator of the child's remaining growth potential.

Height and social status Since a long time the interaction between body height and social status is known. Almost all US American presidents were taller than the average population. Aristocrates and kings used to be 10 to 15 cm taller than farmers, up to the 18th century.

Homo floresiensis is a late Pleistocene hominid fossil from the island of Flores, Indonesia. At present it is debated whether it represent a diminutive, small-brained species or a pathological condition. Individuals with '''microcephalic osteodysplastic primordial dwarfism type II''' (see chapter: The shortest people: pericentrin mutations) have several features in common with Homo floresiensis, including an adult height of about 100 cm, grossly normal intelligence despite severely restricted brain size and a number of minor morphological features.

Insulin-like growth factor-1 (IGF-1) is a potent anabolic protein hormone with high sequence similarity to insulin that is produced by liver cells and by the growth plate chondrocytes. IGF-1 belongs to a complex physiological system necessary for normal tissue growth (see chapter: growth hormone) and not only reflect the availability of growth hormone, but also the nutritional status.

Iso-mortality curves indicate the same risk of dying on height, weight and BMI curves (see: '''Waaler Surfaces''').

Knemometry (greek η κνημη the lower leg) denotes a technical device for measuring the distance between knee and heel, called lower leg length or knee height.

Leptomorph refers to slender persons in the body shape typology of Strömgren (Metric index), in line with metromorph and pyknomorph. The leptomorph type corresponds to leptosom or ectomorph individuals of other typologies.

Leptosom (asthenic) refers to the visual impression of slender persons in the body shape typology of Kretschmer, in contrast to athletic and pyknosom. The leptosom type corresponds to leptomorph or ectomorph individuals of other typologies.

Life history theory is a body of evolutionary biological theory aimed at explaining between- and within-species variation in major features of the life course, especially patterns of growth; reproductive maturation, rate, and periodicity; and mortality.

LGA (Large for Gestational Age) indicates birth weight >90th centile, in contrast to SGA and AGA.

LMS method is recommended  for describing height, weight and BMI in growth references. M stands for mean, S stands for a scaling parameter, and L stands for the Box-Cox power that is required to transform skewed data to normality. Most modern growth references and growth standards use LMS technology.

Longitudinal - in contrast to cross-sectional studies - consist of repeated measurements obtained over long periods of may be several years. Longitudinal growth studies are considered the basis for growth velocity references. The inherent problem of all longitudinal studies is that at the time of publication, the earliest measurements may already be outdated (due to secular trends).

Malnutrition refers to both under and over nutrition based on age and sex-specific standards for anthropometric measurements (typically, WT/AGE, HT/AGE, WT/HT and Upper Arm Circumference, Skinfolds) and/or serological biomarkers (e.g. transferring levels and haemoglobin concentrations for Fe status) and clinical signs (e.g. acanthosis nigricans associated with obesity, Bitot's spots associated with Vitamin A deficiency).

Maturation describes the process that leads to the attainment of final functional capability in biological systems, organs, cells, or in the processing of macromolecules, i.e. posttranscriptional or posttranslational modification.

Menarche (greek μήν month and ἀρχή beginning) denotes the age at which the first menstrual bleeding occurs (see chapter: signs of sexual maturation).

Mesomorphy''' refers to neither stout nor slender persons in the body shape typology of Heath and Carter, in contrast to '''endomorphy''' (stout) and '''ectomorphy''' (slender).

Metric-Index is a sex and age specific weighted sum of height, thoracic breadth, and thoracic depth to classify the type of body shape of individuals of continuous linear variability between slenderness and robustness of the skeleton (leptomorph – metromorph – pyknomorph).

Metromorph refers to intermediate persons in the body shape typology of Strömgren (Metric index), in line with leptomorph and pyknomorph. The metromorph type nearly corresponds to athletic or mesomorph individuals of other typologies.

Mid-parent height refers to the mean of mother's height and father's height. Mid-parent height is sexless, Tanner once defined target height as sex-corrected mean-parent height which has give rise to considerable misunderstandings.

Mid-upper-arm circumference (MUAC) below fixed cut-off values, has commonly been used as a proxy for low weight-for-height (wasting).

Migrants are persons who change residency, either transitorily or permanently.

Mini growth spurts (also referred to as saltation and stasis) are chaotic series of rapid short-term growth changes, first detected in lower leg growth. In human neonates mini growth spurts tend to occur once every 4.2 days, but the time interval between subsequent spurts may vary. They have a mean amplitude of 2 mm (SD 1 mm) and a mean peak growth velocity of 85 µm per hour.

Montbeillard was the first to measure his son once every six months from 1759 to 1777. This document is considered the first longitudinal study of human growth.

Near final height usually indicates that the annual growth rate of a certain individual has declined beyond a certain limit. The term is awkward and should be avoided.

Normal is what frequently occurs. In this book, normality is statistically defined. It relates to the average and to the variation that can be observed within certain limits around the average. Normality does not imply healthiness. And vice versa: measured values outside the confidence limits of normality do not necessarily imply absence of good health. One should therefore avoid the term normal values and instead talk about references.

Obesity is the medical condition of excessive body fat accumulation in adipose tissue, to the extent that it may have an adverse effect on health. Obesity has originally been defined by body mass index above the 95th centile for age, but today, is usually defined by a body mass index above 30 kg/m² in adults. The cut-off BMI in children is lower. Many Asian countries use lower thresholds for obesity

The increasing prevalence of obesity is already visible during childhood. The illness usually starts at early age (5-6 years). Obesity causes many secundary metabolic diseases, diabetes, illnesses of the cardiovascular system, and orthopedic problems.Venus von WillendorfVenus von Willendorf

Obese persons have always been observed. One of the first descriptions is the well-known Venus from Willendorf.

Ontogeny (ontogenesis, morphogenesis) describes origin and development of an organism, in contrast to phylogenetics that describes the evolution of groups of organisms.

Orchidometers (or orchiometer) are strings of numbered wooden or plastic beads of increasing size to accurately determine the size of testes.

Overweight used to be arbitrarily defined by body mass index above the 85th, in other publications by the 90th centile for age. Today, overweight is defined by a body mass index between 25 and 29.9 kg/m² in adults, the cut-offs in children are lower. Many Asian countries use lower thresholds for overweight.

Parent-allowed-for standards make allowance for the height of parents when evaluating child height. They were originally introduced by Tanner and co-workers in 1970, but for a limited age range from 2-9 years. Such standards are important, but failed to gain practical importance. Modern automatized analyses of longitudinal height measurements such as make allowance for parent height.

Pear (gynoid) type''' of fat distribution  on the hips and thighs is believed to serve as energy repository for pregnancy and breast feeding, and is found more often in the females.

Percentile see centile

Phylogenetics describes the evolution of groups of organisms, in contrast to ontogeny that describes origin and development of a single organism.

Physiological pre-term birth and the social uterus reflect that at birth humans compared to other primates, are still premature.

Plasticity is the propensity of a material to undergo permanent deformation under load. In anthropology, the term was first used by Boas in his 1912 US immigrant study to demonstrate the plasticity of human cranial form and in a more general sense, the plasticity of human potential.

Ponderal Index is the cube root of body weight (kg) divided by height (m).

Precision and imprecision denote the variability of repeated measurements, which are due to intra- and inter-observer measurement differences. The most commonly used measure of imprecision is the technical error of measurement (TEM).

Principal Component Analysis (PCA) is a procedure that uses an orthogonal transformation to convert a set of observations of possibly correlated variables into a set of values of linearly uncorrelated variables called principal components. PCA has very successfully been used in describing individual patterns of height and BMI increments.

Psychosexual development as defined by the Consensus Statement on Management of Intersex Disorders, and conceptualized as gender identity, gender role, and sexual orientation, is influenced by factors including androgen exposure, sex chromosome genes, brain structure, social context, and family dynamics.

Puffing of centiles occurs when the population on average enters into puberty. As the fast maturing children start earlier and show their pubertal peak height velocity at younger age than late maturing children, and as on the other hand late maturing children start later, centiles widen at mid-adolescence (see chapter: Growth velocity).

Pyknomorph refers to stout or corpulent persons in the body shape typology of Strömgren (Metric index), in line with metromorph and leptomorph. The pyknomorph type corresponds to pyknosom or endomorph individuals of other typologies.

Pyknosom refers to the visual impression of stout or corpulent persons in the body shape typology of Kretschmer, in contrast to athletic and asthenic (leptosom). The pyknosom type corresponds to pyknomorph or endomorph individuals of other typologies.

Rapid growth – also called accelerated growth – denotes an abnormal condition of overgrowth that is often observed in infancy and early childhood, particularly in small for gestational infants. Rapid growth may not be misinterpreted as catch-up growth, a physiological condition of temporary overgrowth.

References in growth are statistical summaries of anthropometry, conditioned (usually) on age and sex. References describe how children do grow. References are not standards in the sense that they prescribe how children should grow.

Regression toward the mean (or regression to the mean) denotes the statistical fact that any extreme value measured is usually followed by a value that is closer to the average. The phenomenon was first described by Francis Galton as regression towards mediocrity in hereditary stature (

Reproductive strategies differ: the term r strategy describes the energy put into a large number of progeny, with little energy put into the single offspring and thus little survival, whereas K strategy decribes the opposite, little progeny, but more energy put into the single offspring (nutrition in the egg, larger size at birth, or care after birth) and a better chance of survival.  The concept comes from life history theory.

Reserve capacity (RC) as it relates to life history are those somatic resources that exceed the minimum required for sustaining life and allowing reproduction.

Robustness or robusticity of the skeleton refers to the strength of bones as reflected by size and shape. Robustness can be expressed by the frame index.

Rohrer's Index is the weight (kg) devided by the cube of height (m) and thus, similar to BMI (weight divided by the square root of height). Some authors prefer Rohrer's index over BMI, but BMI has become more popular in the obesity literature.

Saltation and stasis see mini growth spurts.

Scelic index = leg length *100/sitting height

Seasonality in growth has world-wide been documented, and usually results from seasonal variation in climate, prevalence of illnesses and the availibility of nutrients. There is little evidence for seasonality in modern children of Western societies, but this was different in former centuries. We found seasonality in German boys from the Carlsschule, Stuttgart, Germany, measured between 1771 and 1793.

Sensitivity describes the ability of a test to identify positive results. The sensitivity of a referral criterium to identify patients with Turner's syndrome among girls is high when a high portion of all patients with Turner's syndrome is dectected.

SGA (Small for Gestational Age) indicates birth weight <10th centile, in contrast to AGA and LGA.

Short stature denotes body height below the third centile for height, but the definition is somewhat vague (in some countries, short stature is defined by -2 standard deviations below mean height for age and gender), and thus encompasses 3% (or 2.3%) of the population – provided the reference values used are valid for that child.

Short term growth refers to increments of height, weight and other anthropometric parameters obtained at short, i.e. at weekly or preferably at daily intervals.


SHOX (short stature homeobox) gene is located both in the pseudoautosomal region of the X chromosome and Y chromosome. Haploinsufficiency of the SHOX gene results in short stature and a number of dysmorphic feature also known in Léri-Weill dyschondrosteosis and Langer mesomelic dysplasia.

Siri's Equation belongs to the body composition equations and simply assumes that the body consists of two compartments: fat mass and fat-free mass.

Skinfold thickness is measured by caliper at exactly defined measuring points, e.g. triceps, subcapular skinfold or hip. Together with bioelectrical impedance analysis (BIA) may give further information about adiposity.

Slaughter's equations predict % body fat (%BF) based on skinfolds separately for children with triceps + subscapular < 35 mm and for children with triceps + subscapular > 35 mm.

Social amenorrhea refers to the marked delay in menarcheal age in European bourgeois societies of the 19th and early 20th century, and in many indigenous societies. We interpret this phenomenon as a mirror of exposure and the individual sensitivity to restrictive codes of sexual behaviour in these societies.

Standard deviation scores (SDS) or Z-scores refer to the difference between the individual measurement (Xi) and the age and sex specific mean values (Xmean) of the reference population, divided by the standard deviation (SD).

SDSi = (Xi - Xmean)/SD

All values between -2 SDS and +2 SDS are by definition considered normal.

Standards in growth describe how children should grow, whereas growth references describe how children do grow.

Stasis see mini growth spurts.

Stunting refers to reduced growth in height and is often due to malnutrition or illness. Stunting may imply solely the tempo component of growth. In this case it is usually followed by catch-up growth. Or it may be a permanent condition causing reduction in final height.

Tall stature denotes body height denotes body height above the 97th centile for height, but the definition is somewhat vague (in some countries, tall stature is defined by +2 standard deviations above mean height for age and gender), and thus encompasses 3% (or 2.3%) of the population – provided the reference values used are valid for that child.

Tanner stages, or Tanner scores describe the visible signs of sexual maturation. Tanner described the developmental stages of the genitals (boys), of the pubic hair (boys and girls), and of the female breast. Stage 1 always describes the pre-adolescent, stage 5 the fully matured adult pattern (see chapter:signs of sexual maturation).


Target height is the expected final height based on mean parental height plus 6.5 cm (boys), respectively minus 6.5 cm (girls). This equation is mathematically incorrect as it ignores parent-parent and parent-child correlations. It should be replaced by calculating conditional target height.

Technical errors of measurement (TEM) are the most commonly used measure of imprecision. The TEM is the square root of measurement error variance.

Tempo refers the progression in biological age and is usually more sensitive than amplitude, to medical treatment, nutrition, health and environmental stress.

Tempo-conditional charts provide centiles that allow for distinguishing between early and late maturing children.

Thoracic index = breast depth * 100/breadth breath

Urban/rural height differences are often cited. Modern urban populations tend to be taller. In the beginning of industrialisation however, living conditions used to be so deleterious in the new social agglomerations that both life expectancy and physical growth and final height were significantly inhibited in most of the large 19th century industrial cities.

Velocity charts provide centiles for the differences in height, weight and other parameters against a standard time interval (usually 12 months).

Waaler Surfaces consist of elliptical lines (iso-mortality curves) that bring height, weight, BMI and the risk of dying into one diagram.

Waist-to-hip ratio (WHR) or waist to hip circumference is the ratio of waist circumference to hip circumference. A WHR in females < 0.85; and in males < 1.0 is considered low risk for coronary heart diseases.

Wasting refers to losses in fat and muscle tissue due to disease or acute or chronic malnutrition. Cut-off points for weight-for-height (WFH) in children may vary, but are often chosen at 80% (close to -2 SD for weight).

Z-scores see Standard deviation scores (SDS)