UNIVERSITY OF LAGOS SCHOOL OF POSTGRADUATE STUDIES APPLICATION
FOR APPROVAL OF TITLE AND SUPERVISORS SECTION A: PARTICULARS OF THE
CANDIDATE NAME: MATRIC No: QUALIFICATIONS: DEGREE IN VIEW: STATUS:
DATE OF REGISTRATION: FIELD OF STUDY: PROPOSED TITLE OF THESIS:
IBEABUCHI, Nwachukwu Mike MS 2113 MB, BS (Lagos), 1985; M. Sc
(Lagos), 1989. Ph. D. Applied Anatomy Staff Candidate M. Phil 1998;
Conversion to Ph. D 2003. Kinanthropometry A kinanthropometric
investigation of the body build and physical growth of adolescent
Nigerian children in urban Lagos.
SECTION B: RESULTS OF COURSE-WORK EXAMINATION COURSE CODE ANT
901 ANT 902 ANT 903 ANT 951 ANT 952 TOTAL UNITS = PROPOSED
SUPERVISORS 1. A.O. Okanlawon (Professor) Department of Anatomy
S.I. Jaja (Associate Professor) Department of Physiology
RECOMMENDATION: The Postgraduate Education Committee at its meeting
held on Wednesday, 11 th May 2005, considered the application and
recommended it to the Academic Board. The Provost is recommending
the application on behalf of the Academic Board to the Board of
Postgraduate Studies for necessary action. NUMBER OF UNITS 4 3 3 3
3 TOTAL G.P.A. = SCORE GRADE GRADE POINT
Professor S. O. Elesha Provost
Dr. (Mrs) A. F. Fagbenro- Beyioku Chairman, Postgraduate
Education Committee. UNIVERSITY OF LAGOS
SCHOOL OF POSTGRADUATE STUDIES DEPARTMENT OF ANATOMY
PROGRESS/SUPERVISORS REPORT IN RESPECT OF Ph.D. CANDIDATE SECTION
A: PARTICULARS OF THE CANDIDATE NAME: MATRIC No: QUALIFICATIONS:
DEGREE IN VIEW: STATUS: DATE OF REGISTRATION: FIELD OF STUDY:
PROPOSED TITLE OF THESIS: IBEABUCHI, Nwachukwu Mike MS 2113 MB, BS
Lagos 1985, and M.Sc Lagos 1989 Ph. D. Applied Anatomy Staff
Candidate M. Phil 1998; conversion to Ph. D 2003. Kinanthropometry
A kinanthropometric investigation into the physique and somatic
growth of a socioeconomically diverse sample of adolescent Nigerian
children in urban Lagos.
SECTION B: RESULTS OF COURSE-WORK EXAMINATION COURSE CODE ANT
901 ANT 902 ANT 903 ANT 951 ANT 952 NUMBER OF UNITS 4 3 3 3 3 TOTAL
UNITS = TOTAL G.P.A. = SECTIONS C: CRITICAL EVALUATION OF THE
RESEARCH 1. Originality of the work SCORE GRADE GRADE POINT
2.
Evidence of Competence in the Field
3.
Interim Assessment of the Candidates Candidate
4.
Potential Worth of the Content of the Research Material for
purposes of Publication.
5.
Potential for Contribution to knowledge
SECTION D AN ASSESSMENT OF PROGRESS IN RESEARCH DURING THE
PERIOD, INCLUDING ANY DELAY OR VERY RAPID PROGRESS IN THE STUDENTS
WORK SECTION E: PARTICULARS OF SUPERVISORS I. II. III. IV. V. VI.
NAME: DESIGNATION: DEPARTMENT: SIGNATURE: DATE: A.O. OKANLAWON
PROFESSOR ANATOMY
------------------------------------------------------------------S.I.
JAJA ASSOCIATE PROFESSOR PHYSIOLOGY
------------------------------------------------------
CHAPTER ONE
1.1 INTRODUCTION The physical structure of the growing child has
been systematically studied for over 150 years (Tanner, 1981). The
basic concepts are built on a strong historical foundation in the
medical, anthropological and human biological sciences. These
studies are often intertwined with studies of physical activity,
performance and fitness of children and adolescents whose
foundation is largely built on what was traditionally called
physical education and what is now called kinesiology, human
kinetics, the physical activity sciences or exercise and sports
sciences. These aspects of human biology have been studied at the
level of the individual as well as in samples of children within
communities and national populations. The study of these phenomena
has contributed to our understanding of human biologic variation. A
significant portion of the biological variation evident among
adults in any population has its origin during the years of growth
and maturation, including the prenatal period. The usual way an
individual can become an adult is through the processes of growth,
maturation and development. These processes have been shown to be
quite plastic. They may be influenced by a variety of environmental
factors operating on the growing and maturing individualnutritional
intake, infant and childhood diseases, patterns of physical
activity and other environmental stresses, which may interact with
the individuals genetic potential for growth and maturation. The
net result is a wide range of variation among individuals. An
important objective would, therefore, be to understand the
biological variability evident during the growing years in terms of
its origin, distribution among different populations and
significance. A vital question would
be why does such variation exist and what does it mean to the
individual? What is the significance of early or late maturity for
behavior and performance of the individual? An issue of current
interest has been the association between growth and maturity, on
the one hand, and between growth and adult health on the other.
This association, in turn, emphasizes the need to continue studies
of growth into the adult years. Early sexual maturity has been
associated with several cancers in adulthood. Overweight
adolescents tend to become overweight adults. Although association
does not demonstrate causality, the results emphasize the need to
consider risk factors for adult diseases within a life span
framework, beginning with fetal growth. In addition to the
foregoing, the study of growth and maturation has provided basic
information relative to several more specific issues. These
include: status, progress, prediction, tracking, comparison and
interpretation of growth and maturity.
1.1.1
Operational Definition of Terms
Growth- this is an increase in the size of the body as a whole
and or the size attained by specific parts of the body.
Hyperplasia- this is an increase in cell number. Hypertrophy-
this is an increase in cell size. Accretion - this is an increase
in intercellular substance. Hyperplasia, hypertrophy and accretion
all occur during growth, but the predominance of one or another
process varies with age and the tissue involved.
The increase in number is a function of cell division (mitosis),
which involves the replication of DNA and the subsequent migration
of replicated chromosomes into functional and identical cells. The
increase in cell size involves an increase in functional units
within the cell, particularly protein and substrates, as is
especially evident in the muscular hypertrophy that occurs during
growth and especially with regular resistance training during
adolescence. The intercellular substances are both organic and
inorganic, and they often function to bind or aggregate the cells
in complex networks, as collagen fibers do in providing the matrix
for the adipocytes of adipose tissue. Postnatal life this is
defined as life after the first month of birth. It is commonly,
although somewhat arbitrarily, divided into three or four age
periods. Infancy - this is the first year of life, up to but not
including the first birthday. This definition is universally
accepted, specifically in the context of worldwide public health.
It is a period of rapid growth in most bodily systems and
dimensions and of rapid development of the neuromuscular system.
Infancy is further subdivided into the following: Perinatal -
around the time of birth, the first week. Neonatal - the first
month of life. Postnatal - the remainder of the first year period
and onwards. Childhood - extends from the end of infancy (the first
birthday) to the start of adolescence. It is often divided into:
Early childhood - this includes the preschool years. In the context
of public health, early childhood extends from the first birthday
through 4 years of age (1.0
to 4.99 years). Early childhood continues the rapid growth and
development of infancy, although at a decelerated rate. Middle
childhood - this generally includes the elementary school years
into primary five and six. Middle childhood extends from 5 years to
the beginning of adolescence. It is a period of relative steady
progress in physical growth and maturation and in behavioral
development. The public health definition of infancy and early
childhood is used for the estimation of infant and childhood
mortality, both of which are accepted universally as indicators of
the health and nutritional status in a community. Adolescence -
This is a more difficult period to define in terms of chronological
age because of the variation in the time of its onset and
termination. The World Health Organization (WHO) defines the age of
adolescence as between 10 and 18 years (WHO, 1995) but certain
authorities (Rolland-Cachera et al., 1991; Suwa et al., 1992; Roche
and Guo, 2001; Malina, Bouchard and Bar-0r, 2004) regard the age
ranges of 8 to 19 years in girls and 10 and 22 years in boys as are
more appropriate limits for normal variation in the onset and
termination of adolescence. In this period, most bodily systems
become adult both structurally and functionally, i.e. they reach
maturity. Structurally, adolescence begins with acceleration in the
rate of growth in stature, which marks the onset of the adolescent
growth spurt. The rate of growth in height reaches a peak, then
begins a slower or decelerative phase, and finally terminates with
the attainment of adult stature. Functionally, however, adolescence
is usually
viewed in terms of sexual maturity, which actually begins with
changes in the neuroendocrine system before overt physical changes
and terminates with the attainment of mature reproductive
function.
Growth curves or tables of body dimensions, performance
variables, and measures of physical activity are ordinarily
presented by chronological age.
Status - This is defined as the attained size or level of
maturity attained at a given point in time. A childs growth,
maturity or performance status relates to how the child compares
with other children of the same age and sex. It also refers to the
status of a group of children in a community. This approach has
often been used in the context of surveys of nutritional status,
physical fitness and general health status. According to the WHO,
for instance, the growth status of children is perhaps the best
indicator of the overall health and nutritional circumstances in a
community, especially in the developing world (WHO, 1995).
Progress - Progress implies change, which provides an estimate
of rate. When taken at several points in time, measurements and
observations of a child or a group of children have provided an
indication of progress over time. A child who grows 6cm over a
period of 1 year would have a growth rate of 6cm/year.
Maturity/ Maturation Maturation is a process, whereas maturity
is a state. Progress also involves maturation. Is the level of a
childs maturity early (advanced), late (delayed) or average
(appropriate or on time) for the childs chronological age? Children
advanced in biological maturity relative to their
chronological age characteristically progress at a more rapid
rate of growth than do those who are delayed in maturity relative
to chronological age and who progress more slowly. Tracking - This
refers to the stability of a characteristic, or the maintenance of
relative rank or position within a group, over time. Distance
(size-attained) curve This curve is a graphical representation of
agespecific and sex-specific averages of growth characteristics for
boys and girls. They do not portray the wide range of normal
individual variability apparent in any group of children. The
pattern of age changes tends to be generally similar in all
children, but the size attained at a given age and the timing of
the adolescent growth spurt varies considerably from child to
child. Reference data - Reference data, sometimes referred to as
norms, are values on the growth and maturity status of a large
sample of healthy children free from overt disease. When a group of
children are studied, they are compared either with reference data
or with other groups of children of the same age and sex. Somatic
growth. This is growth of the external body organs including skin,
subcutaneous tissue, skeletal muscles and bones. Body weight - This
is a measure of body mass. However, the term weight is entrenched
in the literature. Therefore, the terms body mass and weights are
used interchangeably throughout this report. Stature This term
refers to standing height. It is a linear measurement of the
distance from the floor or standing surface to the top (vertex) of
the skull. The two terms are used interchangeably throughout this
report. Stature is a composite of
linear dimensions contributed by the lower extremities, the
trunk, the neck, and the head. Recumbent length - This refers to
the length while lying face up in a standardized position. From
birth to age 2 or 3 years, a childs stature is measured as
recumbent length. As a rule, an individual is longer when lying
down than when standing erect. Sitting height This refers to the
height while sitting. It is measured as the distance from the
sitting surface to the top of the head with the child seated in a
standard position. This measure is most valuable when used with
stature. Leg length (subischial length, or lower extremity length)
This measure refers to stature minus sitting height. It provides an
estimate of length of the lower extremity (Carr et al., 1993).
Diurnal variation This refers to variation of a measurement
during the course of the day. Body weight and stature show diurnal
variation (Reilly, Tyrell and Troup, 1984; Wilby et al., 1985).
Skeletal Breadths These are breadth or width measurements
ordinarily taken across specific bone landmarks and therefore
provide an indication of the robustness or sturdiness of the
skeleton. Four of the commonly taken skeletal breadths include
biacromial, biiliocristal, humerus and femur breadths.
Biacromial breadth measures the distance across the right and
left acromial processes of the scapulae and provides an indication
of shoulder breadth.
Biiliocristal breadth measures the distance across the most
lateral paths of the iliac crests and provides an indication of hip
breadth.
Biepicondylar humerus breadth is taken across the epicondyles of
the elbow while
Biepicondylar femur breadth is a measure of bone breadth across
the knee. Both of these measures provide information on the
robustness of the extremity skeleton.
Limb Circumference This refers to a measure of the circumference
of the limb taken at a specific point the limb.
Skinfold Thickness This refers to the thickness of a double fold
of skin and underlying subcutaneous tissue, can be picked up and
measured at any number of body sites.
Somatotype - A somatotype is a classification of physique based
on the concept of shape, disregarding size. The pre-eminent system
of somatotype classification is the Heath-Carter somatotype. This
shows the relative dominance of Endomorphy (relative fatness),
Mesomorphy (relative musculo-skeletal
robustness) and Ectomorphy (relative linearity). Each component
is identified in the sequence endomorphy-mesomorphy-ectomorphy and,
when
anthropometrically-derived, expressed to the nearest one-tenth
rating, e.g, 1.46.0-3.2, an ectomorphic mesomorph, or
ecto-mesomorph. Ratings of 2 to 2.5 are considered low, 3 to 5 are
moderate, 5.5 to 7 are high and 7.5 and above are very
high(Carter,1996). The derivation equations for each component are
as follows.
Anthropometry - Anthropometry is the study of the human body
measurement for use in anthropological classification and
comparison. Anthropometry
(anthropos = man, metry = measure) is a set of standardized
techniques for systematically taking measurements of the body and
parts of the body, that is, for quantifying dimensions of the body.
Kinanthropometry - this is a branch of anthropometry. The most
common definition is the measurement of human size, shape,
proportion, composition, maturation and gross function as related
to growth, exercise, performance and nutrition. An abbreviated
definition is The quantitative interface between anatomy and
physiology, between morphology and physiology, or between structure
and function (Ross and Marfell-Jones, 1991, Carter and Ackland,
1994; Norton and Olds, 1996). Secular trend this refers to changes
in a physical characteristic that occur from one generation to the
next.
Overview of measurements
1.1.2.1
General
The measurements described herein are the traditional dimensions
utilized in growth studies. They provide information on the size of
the child as a whole (weight and stature) and of specific parts and
tissues. Skeletal breadths describe the overall robustness of the
skeleton; limb circumferences provide information about relative
muscularity, while skinfold thickness is an indicator of
subcutaneous adipose tissue. The specific dimensions include both
the trunk and the extremities. Individuals may be similar in
overall body size
and yet can vary in shape, proportions, and tissue distribution.
Other dimensions may be measured, but the choice of measurements
depends on the information desired in the context of a study.
1.1.2.2 Quality ControlImplicit in studies using anthropometry
is the assumption that every effort is made to ensure the accuracy
and reliability of measurement and standardization of technique.
Also implicit is the assumption that the measurements are taken by
trained individuals. These conditions are essential to obtain
accurate and reliable data and to enhance the utility of the data
from a comparative perspective. Reliable and accurate are
especially critical in serial studies, in which the same child is
followed longitudinally over time, either short-term or long-term,
and in the definition of rather small changes may be necessary and
technical errors associated with measurement can mask true changes.
Error is the discrepancy between the measured value and its true
quantity. Measurement error can be systematic or random. Random
error is a normal aspect of anthropometry and results from
variation within and between individuals in technique of
measurement, problems with measuring instruments (e.g., calibration
or random variation in manufacture), and errors in recording (e.g.,
transposition of numbers). Random error is nondirectional- it may
be above or below the true dimension. In large- scale surveys,
random errors tend to cancel each other and ordinarily are not a
major concern. Systematic error, on the other hand, results from
the tendency of a technician or a measuring instrument (e.g., an
improperly calibrated skinfold caliper or weighing scale)
to consistently under measure or over measure a particular
dimension. Such error is directional and introduces bias into the
data. In addition, the child under observation may be a source of
measurement variability. Replicate measurements of the same subject
are used to estimate variability or error in measurement. Replicate
measurements are taken independently from the same individual by
the same technician after a period of time has lapsed, or they are
taken from the same individual by two different technicians. If the
interval between the replicate measurements is too long (e.g.,
about 1 month) growth may be a factor that contributes to the
variability within or between technicians. Replicate measurements
provide an estimate of within-technician measurement variability,
whereas corresponding measurements taken on the same subjects by
two different individuals provide an estimate of between-technician
measurement variability. The technical error of measurement (TEM)
is a widely used measure of replicability (Malina et al., 1973). It
is defined as the square root of the squared differences of
replicates divided by twice the number of pairs (i.e., the
within-subject variance): = d / 2N The statistic assumes that the
distribution of replicate differences is normal and that errors of
all pairs can be pooled. It indicates that about two-thirds of the
time, the measurement in question should fall within the TEM
(Mueller and Martorell, 1988). Technical errors are reported in the
units of the specific measurement. Within-technician
(intra-observer) and between-technician (inter-observer) TEMs for a
variety of anthropometric dimensions in national surveys and
several more local studies are summarized in Malina (1995).
Although the TEM provides an indicator of the replicability of a
measurement over a short interval of time, it may underestimate the
true measurement error. Variation within an individual child is a
source of error that may not be captured in replicate measurements.
This source may be the result of normal variation in physiology
(for example, muscle tension) and other factors specific to the
child (for instance, temperament, cooperativeness, and stranger
anxiety). This type of error is labeled undependability (Mueller
and Martorell, 1988), and an important component of undependability
is the child factor or the child effect (Lampl et al., 2001).
Accuracy is another component of the measurement process. It refers
to how closely measurements taken by one or several technicians
approximate the true measurement. Accuracy is ordinarily assessed
by comparing measurements taken by the technician(s) with those
obtained by a well trained or criterion Anthropometrist (i.e., the
standard of reference). However, well-trained, expert
anthropometrists also make errors.
1.1.2.3 Ratios and Proportions
1.1.2.3.1. General In addition to providing specific information
in their own right, measurements can be related to each other as
indices or ratios. Ratios are influenced by the relationship
between the two dimensions, and the two dimensions are assumed to
change in a linear manner. Ratios may yield spurious results when
they are based on different types of
dimensions, such as weight and stature or arm circumference and
stature, or when the standard deviations of the dimensions differ
considerably. The ratio may be between dissimilar (different units)
or similar (same unit) measurements.
1.1.2.3.2
Weight and height ratios.
Ratios based on weight and heights have a long tradition in
studies of growth and body build, in studies of undernutrition (low
weight-for-height), and in studies of the risk of overweight and
obesity (excess weight-for-height).
1.1.2.3.3 Weight-for-height. This ratio is commonly used with
preadolescent children especially in the context of severe
malnutrition (for example, kwashiorkor and marasmus) as soft
tissues that constitute body weight (largely muscle and fat) are
wasted. The same occurs in individuals with anorexia nervosa, a
severe eating disorder related to the fear of becoming fat.
Weight-for- stature is also used in the context of overweight.
Youngsters who are overweight have a high weight-for-stature; the
excess weight is related to fatness. However, not all children with
excess weight-for-stature are fat, because muscle mass and other
nonfat tissues may contribute to the increase in weight relative to
stature. This increase is related to body composition. During the
adolescent growth spurt, the relationship between stature and
weight is temporarily changed. The growth spurt occurs, on the
average, first in stature and then in weight, so the relationship
between the two measurements is altered. After growth has ceased,
weight-for-stature is once again a useful index.
1.1.2.3.4
Other weight-height ratios
Sometimes weight is simply expressed relative to height, or
either height or weight is adjusted to account for the relationship
between the two measurements. The adjustment has taken several
forms, for example, weight divided by height squared
(weight/height, the body mass index, BMI or Quetelet index), height
divided by the cube root of weight (height/ weight, the
height-weight ratio, HWR or reciprocal Ponderal index). Except for
ratios of weight and height, the ratios described subsequently are
based on similar measurements (e.g., two lengths or two skeletal
breadths). These ratios are ordinarily calculated by dividing the
larger measurement into the smaller measurement. These ratios
provide information on shape and proportions. Three ratios commonly
used in growth studies are weight-for-stature, sitting
height/stature and shoulder-hip ratios.
1.1.2.3.5
Sitting height/stature ratio
This is the next most widely used ratio in growth studies. It is
calculated as: (Sitting height/stature) x 100
This ratio, also known as the Skelic index (Meredith, 1979;
Monyeki, Pienaar and de Ridder, 1997; Kekana and Monyeki, 1998),
provides an estimate of relative trunk length. It basically asks
the question: what percentage of height while standing is accounted
for by height while sitting? By subtraction, the remaining
percentage is accounted for by the lower extremities. Of two
children with same stature, one may have a Skelic index of
54% and the other 51%. In the first child, sitting height
accounts for 54% of stature, and by subtraction, the lower
extremities account for 46%. This child is said to have relatively
short legs-for-stature. In contrast, sitting height account for 51%
of stature in the second child, and by subtraction, the legs
account for 49%. The second child has relatively long
legs-for-stature compared with the first child.
1.1.2.3.6
Shoulder-Hip Relationships
The ratio of biiliocristal to biacromial breadths is also used
in growth studies. It relates the breadths of the hips (lower
trunk) to that of the shoulders (upper trunk):
(Biiliocristal breadth/biacromial breadth) x 100
This ratio (also known as Androgyny Index) illustrates
proportional changes in shoulder and hip relationships, which
become especially apparent during adolescence. Shoulderhip
relationships also vary among young athletes in several sports
(e.g., track and field, gymnastics and water sports). Young
athletes in these sports generally have proportionally wider
shoulders compared to their hips, and female athletes tend to have
proportionally wider shoulders than non-athletes.
1.1.2.3.7
Other Ratios
Ratios of skinfold thickness measured on the trunk and
extremities are often used to estimate relative subcutaneous
adipose tissue distribution. The ratio of waist and hip
circumferences is also used as an indicator of relative adipose
tissue distribution,
although muscle and skeletal structures also contribute to the
hip girth measurement. Waist circumference by itself is primarily
an indicator of adipose tissue in the abdominal area. The waist-hip
ratio is often used with adults, but it has limited validity as an
indicator of relative adipose tissue distribution in children and
adolescents.
1.1.3
Growth in Stature and Body Weight
Stature and weight are the most commonly used measurements in
growth studies. Both dimensions are often routinely measured on a
regular basis (e.g., in hospitals, schools and sports clubs to
monitor growth status and progress). From birth to early adulthood,
both stature and weight tend to follow a four-phase growth pattern:
rapid gain in infancy and early childhood, rather steady gain in
middle childhood, rapid gain during the adolescent spurt, and slow
increase until growth ceases with the attainment of adult stature.
Body weight, however, usually continues to increase into adult
life. The results of several studies from around the world suggest
that both sexes tend to follow the same course of growth. Sex
differences before the adolescent spurt are usually consistent
although minor. Boys, on the average, tend to be taller and heavier
than girls. During the early part of the adolescent spurt, girls
are temporarily taller and heavier because of their earlier growth
spurt. Girls soon lose the size advantage as the adolescent spurt
of boys occurs; boys catch up with and eventually surpass girls in
body size, on the average. Given the normal range of individual
variation, overlap exists between the sexes
throughout growth and in young adulthood. Hence, some girls are
taller and heavier than most boys at virtually all ages.
Reference Data and Growth Charts Distance curves are commonly
used for assessing the growth status of a single child or a sample
of children. In making such assessments, the size attained by a
child or the average size of a group of children is compared and
evaluated relative to growth data derived from a large sample of
healthy children free from overt disease. These data are referred
to as reference data. They are points of reference in assessing the
growth status of a child or a group of children. The World Health
Organization (1995) defines a reference as a tool for grouping and
analyzing data and provides a common basis for comparing
populations. Reference values are not standards. A standard is
prescriptive and suggests the way things ought to be, and, as such
it has an associated value judgment. Reference values are used.
Reference data are most often presented in the form of several
curves representing different percentiles to accommodate the range
of normal variability among children of the age. Percentiles of
reference data are smooth and ranges are quite broad. Growth charts
used in the United States include the 5th, 10th, 25th, 50th, 75th,
90th, and 95th percentile while those used in the United Kingdom
and South Africa include the 3rd and 97th percentiles in the
list.
The growth charts for the United States (U.S.) children are
based on national surveys that have been regularly conducted since
the 1960s. The surveys are based on complex, multistage stratified
sampling procedures that result in the selection of a sample that
is representative of the noninstitutionalized civilian population.
The National Health Examination Survey (NHES II and NHES III,
1963-1970), the National and Nutrition Examination Survey, NHANES I
(1971-1974) and NHANES II (1976-1980) included adequate numbers of
children and adolescents of Black (African American) and White
(European American) ancestry. NHANES III (1988-1994) over sampled
African Americans and Mexican Americans compared with their numbers
in the total population of the U.S. in 1990. Since 1999, NHANES has
become a continuous survey; the first 2 years of NHANES data
collection (1999-2000) have been used to evaluate changes in
overweight among American children and adolescents (Ogden et al.,
2002) and adults (Flegal et al., 2002). In constructing growth
charts for American children, data from the different ethnic groups
were combined for two reasons. First, the differences in stature
among Blacks, whites, and Mexican Americans was rather small and,
second, the sample sizes for each ethnic group are not satisfactory
to meet the statistical requirements for empirically deriving the
percentiles at the extremes of the distribution (Roche et al.,
1996). In addition, it is not clear whether the apparent growth
differences among the three ethnic groups were genetic. Given the
ethnic heterogeneity of the American population, ethnic- specific
growth charts were not warranted.
Secular trends
The attainment of larger size and the acceleration of maturation
over several generations are collectively labeled as the secular
trend. In this context, the secular trend actually includes several
trends- increase in height and weight during childhood and
adolescence, reduction in the age at menarche and ages at attaining
other indicators of biological maturity, and increase in adult
stature- that have occurred over several generations in Europe and
Japan and in areas of the world largely inhabited by populations of
European ancestry (United States, Canada and Australia). The time
at which secular changes are evident in different populations
varies in part because of the limited availability of satisfactory
data for earlier samples in some populations and because of
differential rates of improvement in health and nutritional
circumstances that underlie improvements in growth and maturity
status. Secular trends are complex phenomena that reflect the
remarkable sensitivity, or plasticity, of the processes of growth
and maturation to the environmental conditions under which children
and adolescents are reared. Secular trends may be positive,
negative or absent. For instance, the observation that children
today are, on average, taller and heavier and mature earlier than
children of several generations ago indicates a positive secular
trend. On the other hand, in some parts of the developing world,
children and adults are shorter than those of a generation or two
ago, or girls attaining menarche later, indicating a negative
secular trend (Tobias, 1985). Lack of change in size or age at
menarche over several generations indicates the absence of a
secular trend, which reflects different situations (Malina,
Bouchard and BarOr, 2004).
Secular trends are not universal and have been shown to be
reversible. This is especially evident in times of war. The
positive secular trend in the heights of children and adolescents
have been temporarily stopped and even reversed in some countries
during World Wars I and II in Europe (van Wieringen, 1986) and
during World War II in Japan (Takaishi, 1995; Ali and Ohtsuki,
2000). When conditions improved after the wars, positive secular
changes in height resumed. More recent examples of the
reversibility of secular trends are apparent in the slightly later
ages at menarche during the period of social and political change
after the collapse of the Soviet dominated communist system in
Poland in the 1980s (Hulanicka et al., 1993) and during the war
conditions that characterized the political breakup of the former
Yugoslavia in the 1990s (Prebeg and Bralic, 2000).
Socioeconomic status The socioeconomic position or status has
been defined as the relative position of a family or individual in
a social structure, based on their access to scarce and valued
resources such as education, wealth and prestige (adapted from
Western, 1983). Three broad conceptualizations of socioeconomic
position or background (social class, socioeconomic status and
disadvantage) have been discussed at length in the sociological,
educational, medical and health literature. An overview of the
major issues which have a bearing on the conceptualization of the
socioeconomic position of schoolchildren, has been presented in a
number of general papers on the history of, and current approaches
to, the conceptualization of social class and socioeconomic status
(Western, 1993; Graetz, 1995a; Jones and McMillan, 2000) while the
conceptualization of socioeconomic
background in educational contexts has been discussed at length
in relation to schooling (Graetz, 1995b) and higher education
(McMillan and Western, 2000; Western et al., 1998). Several studies
have been published in central Europe (Farkas, 1978, 1979, 1980,
1982, 1986; Eiben, 1989, 1994; Eiben et al 1991; Romon et al.,
2005), the United States (Adler et al., 1994; Adler and
Ostrove,1999; Averett and Korenman,1999; Lohman et al., 2000; Mayer
et al., 2005; Rouse and Barrow, 2006), the United Kingdom (Townsend
et al., 1998; Saxena et al., 2004; Wardle et al.,2003, 2004, 2005,
2006), the Meditteranean (Garcia et al., 1993; Rebato et al, 2003),
Australia (Norgan, 1994; Marks et al., 2000; Adams et., 2002)
central Asia (Leung et al., 1996; Ahmed et al., 1998; de Onis et
al., 2001; Wang, 2001), Latin America ( Spurr et al., 1983; Delgado
and Hurtado, 1990; Martinez et al., 1993) and Africa (Toriola,
1990; Cameron, 1992; Simondon et al., 1997; Benefice et al., 1999;
Pawloski, 2002; Gillett and Tobias, 2002; Prista et al., 2003;
Brabin et al., 1997, 2003) that analyze and demonstrate the
relationship between environmental factors such as nutrition,
energy expenditure associated with physical work and the
sociocultural lifestyle and the adolescent childs physical
development. Many of them suggest that remarkable differences in
body dimensions and maturity status may exist between children when
their social background is dissimilar. When material resources
available to the family are ample, the children are often taller
and heavier and reach their respective stages of maturity at a
younger age than their less privileged peers. One of the probable
mechanisms through which these environmental factors may exert
their influence the physique could be energy balance
regulation.
In studying these aspects, research often considers factors that
have been shown to reflect the socio-economic status of the parents
reliably (Townsend et al., 1998; Wardle et al., 2003). Previously
employed indicators include parental level of education (Cesaroni
et al., 2003; Michel et al., 2006; Hagquist, 2007), parental
profession or occupation (Vrijheid et al., 2000; Halldrsson et al.,
2002; Wright and Parker, 2004), family size (Wright, 2000; Blair et
al., 2004; Khang and Kim, 2005), per-capita income (Woodroffe et
al., 1993; Pattenden et al., 1999; Vrijheid et al., 2000;
Alvarez-Dardet and Ashton, 2005;), the grade of provision with
modern conveniences of the habitat (Cooper et al., 1998; Saxena and
Majeed, 1999; Saxena et al., 2002), the settlements level of
urbanization and the number of inhabitants living in the community
(Office of Population, Censuses and Surveys. 1993; Forrester et
al., 1996; Office for National Statistics, 2002), the level of
health care and access to medical services (Newton and Goldacre,
1994; Roland et al., 1996;Department of Health, 2001; Hippisley-Cox
et al., 2002; Office for National Statistics, 2002; Petrou and
Kupek, 2005). The socio-economic status of the family is often
reflected in the type of school attended by the children in the
family ((McMurray et al., 2002; Wardle et al., 2006 etc).
Economically advantaged families often prefer fee-paying, private
school to minimal feepaying public school because the former tend
to be better funded to provide adequate educational facilities and
a good learning environment (Heckman and Lochner, 2000; Vegeris and
Perry, 2003;US Department of Education NCES-2005). Furthermore, the
discriminatory tendency in the funding pattern of public schools in
various countries has been well documented (Hedges et al., 1989,
1994; Hanushek 1996; Ellwood and Kane 2000; Krueger, 2003; Adelman
et al., 2003) and is a reflection of
institutionalized social class as well as the inequalities and
disadvantage consequent for the poorer segments of the society.
Socioeconomic disadvantage has been measured in epidemiological
studies by both individual indicators (education, occupation, house
ownership, quality and amenities, income) and by area-based
indicators which are indices based on an array of social
characteristics of residential areas drawn from census data or
aggregate income (Krieger et al., 1997; Geronimus and Bound, 1998;
Geyer and Peter, 2000). This would have implications for the
attainment of the full educational, psychological and physical
growth potential of the adolescent child (Barrow and Rouse, 2004;
Spencer, 2005). Although different by definition, social class and
socioeconomic status are closely intertwined (Graetz 1995a; Jones
& McMillan 2000; Western 1993). However, their combined roles
in influencing the health and growth status of children especially
in Africa is more readily apparent because the public welfare
institutions expected to provide the social support services that
could ameliorate the effects of social inequality are either
moribund or non-existent (Spencer et al., 1999; Marks et al., 2000;
Snyder et al., 2003; Hanushek et al., 2005). In several countries,
attempts have been made to address this problem comprehensively but
differ in specific actions or in the focus of their educational
reforms (Rouse, 1997; Marks et al., 2000; Howell and Peterson,
2002; Mullis et al., 2002; Bifulco and Ladd, 2004; Hanushek et al.,
2005). Two options, decentralization of the school system and free
school choice, have become a part of the global trend in
educational reform (Chapman, 1996; Gonnie van Amelsvoort and
Scheerens, 1997). The methods used have varied with the countries
(Liberatos et al., 1988; Durkin et al., 1994; Statistics Norway,
1984), with the age group of children (Mueller and Parcel, 1981;
Anderssen, 1995; Currie et al., 1997) and with the nature of
study (Abramson, 1982). Some studies measured or classified the
socioeconomic status of schools for the purposes of
government-funding of public and privately-owned schools (DETYA,
1999; Marks et al., 2000; Rouse and Barrow, 2006). Commonly-
adopted procedures include such parameters as the facilities
provided by the school (Hedges et al., 1994; Hanushek, 1996; Snyder
et al., 2003; Aaronson et al., 2005) and the demographic
characteristics of its geographical location (Australia Board of
Studies 1990, 1994, 1998). Sometimes the classification may be
census-based (Ross, 1983; Ross et al., 1988) wherein the process is
integrated into the countrys national demographic survey (Linke et.
al. 1988; Western et. al. 1998). In other situations, it has been
determined by the socioeconomic status of the parents of the
schoolchildren (Chen et al., 2006). Some authorities recommend that
the socioeconomic status of the parental breadwinner only or the
entire family income (Morris et al., 2004; Dahl and Lochner, 2005)
or a scored-index representing the combination of a number of
criteria (Graetz 1995; Townsend et al., 1988; DETYA, 1998; Wardle
et al., 2002) be used to determine the socioeconomic status for the
study. Other authorities have considered the characteristics of the
school only as an adequate indicator of the socio-economic status
of the study children, thereby avoiding the intrusiveness often
associated with trying to obtain accurate information about a
familys wealth (Finn and Achilles, 1990; Angrist and Lavy, 1999;
DETYA, 1999; Hoxby, 2000; Snyder et al., 2003). Sometimes the
information has been obtained from the childs self-reporting of
fathers income (Looker, 1989; West et al., 2001; Lien et al.,
2001). The non-uniformity of the classification systems is further
complicated by confounding issues such as misclassification of
individuals and schools due to assumed homogeneity of the
population characteristics (Western, 1988; Starfield et al., 2002).
Whichever method is
adopted the principle has been that proper validation would be
required in the context of the specific study (Starfield, 1985;
Ainley & Marks 1999; DETYA, 1999; Janssen et al., 2006). A
review of relevant literature from different regions of Africa
(Pawloski, 2002; Prista et al., 2003) and Nigeria (Omololu et al.,
1981; Brabin et al., 1997; Abidoye and Nwachie, 2001) suggests that
usually it is the minimal criteria that have been adopted among the
adolescent age group. The Nigeria DHS EdData Survey (2004), jointly
published by the National Populations Commission of Nigeria (NPC)
and the Federal Ministry of Health in collaboration with ORC Macro
of Calverton, Maryland, USA and the United States Agency for
International Development (USAID) presents health and demography
data for the Nigerian population based on the 1991 Census data. In
accordance with the WHO recommendation, anthropometric measurements
were taken to derive three nutritional status indices including:
height-for-age, weight-for-age and height-for-weight. These data
for Nigerian schoolchildren have been compared with the
international reference population defined by the US National
Centre for Health Statistics (NCHS) and accepted by the Center for
Disease Control and Prevention (CDC). Each of the status indices
has been expressed in standard deviation units (z-scores). The use
of this reference population was based on the finding that
well-nourished children from all populations (where data exist)
follow very similar growth patterns up to the onset of puberty
(Drake et al., 2002; Partnership for Child Development, 2000).
Consequently, the NDES has not used data for children older than 9
years 11 months. The age range of the current dissertation is from
9 years 6 months to 16 years 6 months.
Somatotype A somatotype is a classification of physique based on
the concept of shape, disregarding size. The pre-eminent system of
somatotype classification is the Heath-Carter somatotype. This
shows the relative dominance of Endomorphy (relative fatness),
Mesomorphy (relative musculo-skeletal robustness) and Ectomorphy
(relative linearity). Each component is identified in the sequence
endomorphy-mesomorphy-ectomorphy and, when
anthropometrically-derived, expressed to the nearest one-tenth
rating, e.g, 1.46.0-3.2, an ectomorphic mesomorph, or
ecto-mesomorph. Ratings of 2 to 2.5 are considered low, 3 to 5 are
moderate, and 5.5 to 7 are high and 7.5 and above are very high
(Carter, 1996).
Kinanthropometry Kinanthropometry is a scientific specialization
in exercise science that has brought specialists from human
anatomy, human biology, physical anthropology, physical education,
exercise physiology, sports science, sports medicine, and
nutrition, pediatrics, gerontology, cardiology, respiratory
medicine, neurology, orthopedics and several other medical
disciplines into close alliance. Thus, its scope and applications
are broad (Carter, 1996). Kinanthropometry deals with the
measurement of humans in a variety of morphological perspectives,
its application to movement, and those factors which influence
movement, including: components of body build, body measurements,
proportions, composition, shape, and maturation, motor abilities
and cardiorespiratory capacities, physical activity including
recreational activity as well as highly specialized sports
performance.
Ross (1978) presented an elegant overview of the specialization.
The definition of size includes the measurement of absolute
dimensions of the body, both external and internal; shape refers to
the assessment of the form of the body; proportion refers to the
relative size or relationship of body parts of one another or to
the whole body; composition includes the assessment of the various
tissues, fluids and compartments of the body; maturation refers to
the assessment of the biological age or maturity status of the
person; and gross function includes performance in sports, events,
tasks, occupation or fitness tests. Although kinanthropometrists
often examine the technology within one of the above areas, a
kinanthropometric study would have at least one element of
morphology or structure along with gross motor performance or
application in one of the areas of growth, exercise, performance or
nutrition.
Uses of Kinanthropometry Kinanthropometric measurements, when
analyzed statistically, may be utilized in a wide variety of ways
including: somatotyping, fractionation of body mass into bone,
muscle, fat and residual components, body proportionality
estimates, prediction of body density and composition,
determination of chronological and biological age, assessment of
nutritional status and monitoring of nutrition interventions,
assessment of growth patterns and estimation of growth indices in
children and the youth, prediction and assessment of adult stature,
prediction of performance, health and survival in the general
population, assessment and monitoring of lifestyle- related
illnesses, monitoring of athletic development and performance,
comparison between national and international sample groups,
physical anthropological classification of population groups,
guiding public
health policy and clinical decisions, design of office and home
furniture, design of shoes and garments, design of orthopedic and
physiotherapy aids and gadgetry, design of indoor and outdoor
fitness and wellness equipment, management of life insurance
policies and production and revalidation of reference values,
(Astrand and Rodahl, 1970; Ross and Marfell-Jones, 1991; Amusa,
Igbanugo and Toriola, 1998).
Anthropometric assessment protocols The protocols for specific
measurements have been discussed in Lohman et al. (1988), Ross and
Marfell-Jones (1991), and Norton and Olds (1996). Anthropometry
depends upon strict adherence to particular rules of measurement as
determined by national and international standards bodies.
Anthropometry is a very old science, and like many old sciences,
has followed a variety of paths. The diversity of anthropometric
paths is both its richness as well as its bane. One of the
consequences of multiple anthropometric traditions has been the
lack of standardization in the identification of measurement sites,
and in measuring techniques. This has made comparison across time
and space extremely difficult. In the year 2001, the International
Society for the Advancement of Kinanthropometry (ISAK) published
its reference manual, International Standards for Anthropometric
Assessment, as a practical tool for use in teaching, in the
laboratory and in the field. Derived in a large part from a
previous, well- recognized standard, Chapter 2 of Anthropometrica,
edited by Norton and Olds (1996) as well as from a series of
classic textbooks and congress reports generated throughout the
20th century, this reference manual was developed over a period of
five years after extensive consultation within its
Executive council, with all ISAK Criterion Anthropometrists and
many ISAK Level 3 anthropometrists. It is an update on all the
protocols currently in use for anthropometry worldwide. It was
endorsed by United Nations Educational, Scientific and Cultural
Organization (UNESCO) and the Supreme Council for Sports in Africa
(SCSA) for use during the 8th All-Africa Games in Abuja, Nigeria
(October 4- 18, 2003) by the Nigeria All-Africa Games
Kinanthropometry Project (NAAGKiP) Research Team, that obtained
kinanthropometric data from the elite athletes competing at those
Games. The anthropometric sites and measurement procedures
preferred for the current study are those based the international
standards recommended by ISAK. These measurements provide a
comprehensive description of the kinanthropometric data, which
could be used to derive additional computations such as: estimates
of relative body fat (using a large number of prediction
equations), estimates of bone, muscle, adipose and residual masses
using fractionation of body mass techniques (Drinkwater and Ross,
1980; Kerr, 1992), calculation of skeletal mass and skeletal muscle
mass by various methods (Martin et al., 1990; Martin, 1991; Janssen
et al., 2000; Lee et al., 2000).
CHAPTER TWO
2.1
LITERATURE REVIEW
2.1.1 Growth Studies: Sources of Data A review of the history of
the study of growth suggests that the earliest published work on
the subject was based on data generated from North America and
Europe. A detailed account was published in Origins of the Study of
Human Growth, (Boyd, 1980), and A History of the Study of Human
Growth, (Tanner, 1981). Boyd (1980) was based on the unfinished
manuscripts of Richard Scammon, which were first reported in 1923
in the 11th edition of Morris Anatomy and subsequently republished
in his 1930 Sigma XI lecture (Scammon, 1930). Boyd (1980)
considered early discussions of the life cycle (including
description of prenatal and postnatal stages) from antiquity to
1700 and then more specific studies of growth in Europe and North
America from 1700 to 1940. Tanner (1981) briefly considered the
ancient world, the middle Ages, and the Renaissance and then
presented a comprehensive discussion of growth studies from the
18th century through the major North American and European
longitudinal studies. Earlier reports provide an excellent
background to the relatively long history of the study of growth in
Europe and the United States. Meredith (1936) reviewed American
research on growth of children before 1900, and Krogman (1941)
provided a comprehensive compilation of European and North American
growth studies before 1940, focusing primarily on data from the
1920s and 1930s. The compilation also included several studies of
active youth and of motor performance. Krogman (1950, 1955) also
presented a syllabus of concepts and techniques for the study of
growth, including motor skills, which was followed by a summary of
related literature published between 1950 and 1955. Meredith (1969,
1971, and 1987) also reported summaries of data from different
areas of the world dealing with specific body dimensions in
specific age groups between birth and adulthood. Roche and Malina
(1983) provide detailed tabular summaries for a variety of
indicators of growth and maturity in North American since 1940 in a
two-volume compendium, Manual of Physical Status and Performance in
childhood. Eveleth and Tanners (1990) Worldwide Variation in Human
Growth is a compendium of data on growth and maturation from many
regions of the world and also includes a discussion of factors that
influence these processes.
Longitudinal Studies of Growth and Maturation 2.1.2.1 United
States Studies. Several longitudinal studies were begun in the
United
States in the 1920s and early 1930s: the Harvard School of
Public Health in the Boston area; the Brush Foundation Study at the
Western Reserve University (now Case Western Reserve University) in
Cleveland, Ohio; the Fels Research Institute in Yellow Springs, in
south-central Ohio (now a part of the Wright State University
School of Medicine); the Child Research Council in Denver,
Colorado; and the Guidance Study of the University of California at
Berkeley (Tanner 1948, 1981). These major United States studies
included children between 11 and 17 years of age (Espenschade,
1940; Jones, 1949). Two more recent American longitudinal studies
of growth took a different approach than the traditional studies.
The first was based on a longitudinal series of about 340
middleclass girls from Newton, Massachusetts, followed from 9 or 10
years of age to young adulthood. The study was begun in 1965 and
included stature and weight and age at menarche. This study is
unique in that the data were reported by the mothers of the
girls
in questionnaires sent at monthly or 6-week intervals. The
reported data were supplemented by semiannual or annual height and
weight measurements made by the physical education department of
the local school system, beginning when the girls were 5 or 6 years
of age. Measurements of growth and maturity that span childhood and
adolescence provide the basis for many longitudinal analyses. Other
growth studies, some of which of which included a longitudinal
component, were carried out since 1917 at the Iowa Child Welfare
Research Station at the University of Iowa in Iowa City. The
Philadelphia Center (now the W.M. Krogman Center) for Research in
Child Growth at the University of Pennsylvania carried out a mixed-
longitudinal study of school-age American Black (African American)
and White (European American) children from the late 1940s through
the late 1960s (Krogman, 1970). Many of the subjects of the Fels
study were followed into adulthood in a series of studies that
continues at present (Roche, 1992). Data from the Fels and Harvard
studies are also being analyzed in the context of tracking of
fatness and other risk factors for disease from childhood into
adulthood and tracking of precursors of morbidity and mortality in
adulthood (Casey et al., 1992; Must et al., 1992; Guo et al.,
1994). In addition to the Guidance Study at the University of
California, a second study, the Adolescent Growth Study of children
in Oakland, California, was conducted. This study included
measurements of strength and motor performance of children and
adolescents age (Zacharias and Rand, 1983). The second study, the
Harvard Six Cities Study, is part of an examination of the health
effects of indoor and outdoor pollution on children from six
regions of the United States (localities in Massachusetts,
Tennessee, Ohio, Missouri,
Wisconsin and Kansas). Annual examinations included height and
weight measurements, in addition to spirometry, a measure of lung
function (Berkey et al., 1993).
2.1.2.2 European Studies. After the initial series of
longitudinal studies in the United States, the emphasis on
longitudinal growth studies shifted to Europe. The Harpenden Growth
Study in the suburbs of London was begun in 1948 and included
measurements of size, physique, body composition and maturation
(Tanner, 1981). The setting for the study was a childrens home.
Before entering the home, most of the children had probably lived
under socially disadvantageous conditions. However, the children
were well cared for at the home and lived in relatively small
cottages or family groups. The Harpenden Growth Study was followed
by a series of longitudinal studies in several European cities that
were begun in the mid-1950s. The studies were coordinated by the
International Childrens Center in Paris and included separate
longitudinal samples in Brussels, London, Paris, Stockholm and
Zurich (Tanner, 1981). These studies focused primarily on growth
and maturation from birth through adolescence. Another European
longitudinal study, independent of those coordinated by the
International Childrens Center, was the Wroclaw Growth Study in
southwestern Poland, which was begun in 1961. A large cohort of boy
and girls was followed from 8 to 18 years of age (Bielicki and
Waliszko, 1975; Waliszko and Jedlinska, 1976). The study also
focused primarily on measures of growth and maturation. Some other
European studies require mention. Height, weight, and secondary
sexual characteristics of about 700 urban schoolchildren from
several centers in Sweden were monitored from 10-16 years of age in
girls and from 10-18 years in boys between 1964
and 1971 (Lindgren, 1979). In a similar study, about 1400
schoolchildren in Newcastleupon- Tyne, England, were followed from
9 to 17 years of age beginning in 1971 (Billewicz et al., 1983).
The variables included measures of growth and secondary sex
characteristics. In both studies, children were examined twice a
year at approximately half-yearly intervals. Two generally similar
longitudinal studies were begun in the Netherlands in the 1970s,
the Nijmegen Growth Study (Prahl-Andersen et al., 1979) and the
Study of the Growth and Health of Teenagers in Amsterdam (Kemper,
1995). The Amsterdam Study includes measurements of growth,
maturity, motor performance, aerobic power and habitual physical
activity and also continues into adulthood with a cohort of males
and females followed at about 21, 27 and 30 years of age. A
sampling procedure that allows for the proportionate representation
of the ethnic African and Caribbean communities resident in this
particularly multicultural metropolis makes the study quite unique.
This effort later inspired the commencement, in South Africa, of
the Ellisras Longitudinal Study in 1996, the first of its kind in
sub- Saharan Africa (Monyeki et al., 1999).
2.1.2.3 Risk Factors for Disease in Longitudinal Studies. Given
concern for coronary heart disease in adults, several relatively
recent studies have focused on the development of risk factors for
coronary heart disease (e.g., high levels of serum lipids with
abnormal lipoprotein profile, hypertension and obesity) in children
and youth. Coronary heart disease is one the leading causes of
death in North American adults, and many of the risk factors for
the disease develop during childhood (Berenson, 1986; Kannel et
al., 1995). Several studies have attempted to track or follow the
development of risk factors during
childhood and adolescence; the studies thus have a longitudinal
component. These studies include, for example, the Bogalusa Heart
Study of black and White children in Louisiana (Berenson et al.,
1995), the Muscatine Study of primarily White Iowa school children
(Lauer et al., 1993), and the Cincinnati Lipid Research Clinics
study of Black and White children in the Princeton school district
(Morrison et al., 1979). The studies were begun in the 1970s and
include a variety of coronary heart disease risk factors in
addition to measures of growth and maturation. The studies so far
described all include a longitudinal component, but given the
logistical problems encountered in doing such studies and the
relatively large data sets involved, the studies are basically
mixed-longitudinal. Results of the longitudinal and
mixedlongitudinal components of these are used subsequently to
illustrate patterns of growth, maturation and the range of normal
variation inherent in any group of children.
2.1.2.4 African Studies Omololu et al. (1981) reported a
transverse- longitudinal study of heights and weights of children
in a Nigerian village. In May 1996, the University of the North,
Sovenga, in the Northern Province of South Africa, initiated a
longitudinal study in the Ellisras rural community in the Northern
Province (now Limpopo Province) of South Africa. This study
examined physical growth patterns, nutritional status and
socioeconomic indices of rural children. Three years later, the
Vrije University, Amsterdam, in the Netherlands, joined the project
and then other lifestyle related parameters such as blood pressure,
24hours recall of nutritional intake of children and oral glucose
tolerance test were included in the project (Monyeki, 2003).
Subsequently, a 3-year prospective study on high levels
of habitual physical activity in West African adolescent girls
and relationship to maturation, growth, and nutritional status, was
reported from Senegal (Benefice, Garnier and Ndiaye, 2003).
2.1.3. Cross-sectional Surveys of Growth and Maturation.
2.1.3.1. General Overview. In addition to the longitudinal studies,
a variety of crosssectional studies provide important information.
These studies include several national surveys. For example,
nationwide surveys of height, weight and sexual maturation of Dutch
children in the Netherlands were conducted in 1955, 1965 and 1980
(Roede and van Wieringen, 1985). In Western Australia, the
Busselton Survey is a population survey that has been held every
three years in the Perth metropolitan area and rural Busselton
since the 1970s. In 1994-1995 a re-survey was held of all past
participants and 8,502 attended. The measurements included stature,
body weight, skinfolds, limb and trunk circumferences and blood
pressure. The significance of this survey is that financial
constraints have precluded the employment of full-time staff for
data collection and is, therefore, done by unpaid lay volunteers
(Adams et al., 2002). Since the 1960s, the United States National
Center for Health Statistics has conducted national surveys on a
regular basis. Most of the surveys include height and weight, and
several include a more extensive series of body measurements. These
national surveys are unique in that all of them use a sampling
design that permits estimates for the total United States
population or for specific ethnic groups. Data from the United
States national surveys provide the basis for charts of height,
weight and other dimensions or indices that are used to assess the
growth status of children and adolescents around the world.
2.1.3.2. African Studies. A number of studies have examined
stature and weight in selected populations, as well as growth and
development in children. Tobias (1975), working in South Africa,
summarized adult stature from 123 samples and noted that there was
no secular trend. However, a reduced sexual dimorphism did exist
with respect to stature in African populations compared to
Europeans. More recent studies by other groups in South Africa led
by Cameron (Cameron, 1984, 1991, 1992; Cameron et al., 1992;
Cameron and Getz, 1997; Monyeki, 1999, 2000; Monyeki et al., 1999,
Monyeki et al., 2000) and Walker (Walker et al., 1979; Walker et
al., 1989; Walker et al., 1990) have compared rural and urban
communities in addition to examining various body composition
parameters such as obesity, body fat patterning, lipidemias and
other risk factors for adult diseases. Other more recent
cross-sectional studies include the prevalence and severity of
malnutrition and age at menarche among adolescent schoolgirls in
western Kenya (Leenstra et al., 2005), a cross-cultural comparison
of growth, maturation and adiposity indices of two contrasting
adolescent populations in rural Senegal (West Africa) and
Martinique (Caribbean) (Benefice, Caius and Garnier, 2004), the
nutritional status, growth and sleep habits among Senegalese
adolescent girls (Benefice, Garnier and Ndiaye, 2004), the impact
of the health and living conditions of migrant and non-migrant
Senegalese adolescent girls on their nutritional status and growth
(Garnier et al., 2003), and the timing of reproductive maturation
in rural versus urban Tonga and Zambia boys (Campbell,
Gillett-Netting and Meloy, 2004). Several other studies including
the influence of urban migration on physical activity, nutritional
status and growth of Senegalese adolescents of rural origin
(Garnier, Ndiaye and Benefice, 2003), have related growth to
performance and physical activity.
2.1.3.3. Nigerian Studies. The profile of growth studies
conducted in Nigeria is not very illustrious. The earliest known
report of any related study was that of the prevalence of obesity
among Nigerian school children living in the Abeokuta metropolis in
southwest Nigeria by Akesode and Ajibode (1983). Other reports are
few and far between. Owa and Adejuyigbe (1997) reported a
comparison of measurements of fat mass, fat mass percentage, body
mass index and mid-upper arm circumference taken by anthropometric
and bioelectric impedance techniques in a healthy population of
Nigerian school children aged 5-15 years resident in Ile- Ife, also
in Southwest Nigeria. More recent studies by Ansa et al. (2001)
examined the profile of body mass index and obesity in Nigerian
children and adolescents aged 6-18 years resident in Calabar, in
the deep-south Nigerian region, while the freshly published report
on the body composition of normal and malnourished children aged
3-11 years in the Niger Delta region by Eboh and Boye (2005) has
given an indication of current research directions. However, since
the pioneer efforts of Toriola and Igbokwe (1985) in determining
the relationship between perceived physique and somatotype
characteristics of 10-18 year old boys and girls resident in Iseyin
in rural southwest Nigeria, only the singular report by Owolabi and
Makpu (1994) on the body composition and somatotype of professional
Nigerian division one male soccer and basketball players have been
cited in the literature regarding the study of the shape and
physique of Nigerian children and youth. These observations,
therefore,
underscore the depth of the inadequacy of information regarding
the growth, maturation, physical and nutritional status among
Nigerians.
Cross- Sectional Surveys of Performance and Physical Activity.
The American Alliance for Health, Physical Education and Recreation
(1976) has conducted national surveys of the motor fitness of
American school-age children in 1958, 1965, and 1975, and the
Presidents Council on Physical Fitness and Sport (Reiff et al.,
1986) conducted a similar survey in 1985. National surveys of the
health-related physical fitness of children 6 to 9 and 10 to 17
years of age, respectively, the first and second National Children
and Youth Fitness Surveys, were conducted in 1984 and 1986 (Pate
and Shephard, 1989). Motor fitness focuses on performance in a
variety of tasks, whereas health-related fitness focuses on
indicators of cardiovascular fitness, strength, flexibility, and
fatness. The National Children and Youth Fitness Surveys also
included indicators of habitual physical activity. The Canadian
Fitness Survey (1985), carried out in 1981, included measurements
of physical activity, body size, fatness, physical performance and
physical activity for a nationally representative sample of
children and youth. A subsample of the Canada Fitness Survey was
measured again 7 years later (Stephens and Craig, 1990). The Africa
Association for Health, Physical Education, Recreation, Sport and
Dance (AFAHPER-SD), modeled after the pattern of the American
Alliance, organized its first Africa Regional Conference on
Physical, Health Education, Recreation and Dance (ARCPHERD), in
October 1994 at Gaborone, Botswana. The proceeding of the
conference was published in the same year as Health, Physical
Education, Recreation
and Dance in Africa (Amusa, 1994). Subsequently, the African
Journal for Physical, Health Education, Recreation and Dance
(AJPHERD), a peer-reviewed biennial publication of the association,
was established. The first issue of this journal was released in
April 1995. The journal has since become a cornerstone in the
literature and an arrowhead in the advancement of kinanthropometry
and growth research in Africa, in particular, through its numerous
and regular publications, frequently contributed by frontline
researchers worldwide. Another significant direct consequence of
the Gaborone meeting was the establishment of the All- Africa Games
Kinanthropometry Project (AAGKiP) by top researchers from all over
Africa based in Southern Africa. Work commenced in October 1995 at
the 6th AllAfrica Games held in Harare, Zimbabwe during which the
kinanthropometric characteristics of the elite Africa athletes
participating at those Games were profiled. This was the first of
its kind anywhere in Africa, by African researchers on African
athletes. The Supreme Council for Sport in Africa (SCSA) endorsed
the project. It was modeled after the protocols used to assess
athletes attending the Olympic Games, beginning in 1928, and later
modified by Carter and his colleagues at the Montreal Olympics in
1976 and also at the 1991 World Swimming Championships, Melbourne,
Australia. The success of the Harare AAGKiP encouraged the team to
repeat the exercise at the 1999 edition held in Johannesburg, South
Africa. By this time, the project had come to enjoy the additional
and full support of the United Nations Educational and Scientific
Organization (UNESCO). Prior to the commencement of the 3rd edition
of the project at the 8th All-Africa Games held in Abuja, Nigeria
in October 2003, the International Society for the Advancement of
Kinanthropometry (ISAK) held its first ever
Anthropometry Accreditation and Certification Course for Level 2
Technicians in Africa in the month of September, 2003 in Abuja.
This course, moderated by J.E.L. Carter, was designed to train the
anthropometry technicians in preparation for the Nigeria All-Africa
Games Kinanthropometry Project (NAAGKiP) and to upgrade the
protocol used at the previous two editions (de Ridder, 2003).
Through encouragement and careful guidance by the late A.O.
Ajiduah, the exercise physiologist and Professor of Human Kinetics
and Health Education in the University of Lagos, this investigator
was able to receive training and to participate in the NAAGKiP as
Anthropometry technician- Level 2. The All-Africa Games
Kinanthropometry Project, therefore, has become Africas first
continental survey for performance and physical activity. It is
pertinent to note, however, that the effort has been directed at
generating data from the adult, elite athlete and not the junior,
growing athlete. The uses of anthropometry as a tool for
investigating the relationship between growth, maturity, physical
activity, health and performance has been much more vigorously
explored by researchers in physical education (currently referred
to as human kinetics), exercise physiology and sports medicine.
Investigators in these fields of endeavor interact frequently
through annual conferences and participation at University,
National and International Sports meetings. In Nigeria, they
collaborate through an umbrella body known as the Nigeria
Association for Sports Science and Medicine (NASSM) and the results
of these efforts are published regularly in their journal, the
Nigerian Journal of Sports science and Medicine. However, their
efforts have usually been directed towards the care of the injured
athlete and other factors related to health, fitness, physical
activity and performance, with very limited input from
investigators involved in growth research.
Only a few papers have appeared in the literature in recent
times (Musa and Lawal, 2001; Emiola, 2002; Okuneye et al., 2004;
Okuneye, Ogunleye and Ibeabuchi, 2004), which reported on children.
Although national surveys are cross-sectional, they are useful
because the subjects selected to participate in the surveys are
chosen to be representative of the population as a whole. Such
samples are known as national probability samples. Results of such
largescale national or continental surveys are the primary source
for the construction of reference data used in comparing and
evaluating the growth, maturity and performance status of
children.
Current status of somatic growth research
Thus, it has been shown that the study of growth and maturation
has a long history spanning over 150 years in the disciplines of
medicine, human biology, biological anthropology and the sports
sciences (Krogman, 1970; Meredith, 1971, 1987; Malina, 1978; Garn,
1980; Tanner, 1981, 1989; Malina and Roche, 1983; Roche and Malina,
1983; Faulkner and Tanner, 1986; Eveleth and Tanner, 1990; Roche,
1992). The concepts and principles that underlie the study of
growth and maturation during the first two decades of postnatal
life have been well elaborated and developed in the early part of
the 20th century (Scammon, 1930; Krogman, 1948). The major sources
of information, longitudinal and cross-sectional studies for the
understanding of growth and maturation, have also been identified
(Krogman, 1970; Meredith, 1971, 1978, 1987; Bielicki and Waliszko,
1975; Eveleth and Tanner, 1976, 1990; Waliszko and Jedlinska, 1976;
Malina,
1978; Lindgren, 1979; Tanner, 1981; Malina and Roche, 1983;
Roche, 1992; Guo et al., 1994; Billewicz et al., 1983; Adams et
al., 2002; Monyeki, 2003). The study of growth is largely
synonymous with measurement (McCammon, 1970; Malina and Roche,
1983; Tanner, 1989). The systematic study of these features, which
are characteristic for every individual, requires measurements
taken at different ages during infancy, childhood and adolescence
and continuing into young adulthood (Lohman, Roche and Matorell,
1988; Mueller and Matorell, 1988; Malina, 1995; Norton and Olds,
1996; ISAK, 2001; Lampl et al., 2001). Measurements commonly used
in growth studies have been described and the changes in body size
and specific dimensions and body proportions that occur as the
individual passes from infancy through childhood and adolescence
into young adulthood have been reviewed and summarized (Malina,
Hamill and Lemeshow, 1973, 1974; Meredith, 1978; Roche and Himes,
1980; Tanner 1981; Matorell et al., 1988; Lindgren et al., 1994;
Kuczmarski et al., 2000). Two measurements that are basic to most
growth studies, height and weight, and more recently, the body mass
index (BMI, weight/ height ) have been used in many nutritional
surveys (Tanner, Whitehouse and Takaishi, 1966; Roche, 1972; Roche,
Guo and Yeung, 1989; Kuczmarski and Johnson, 1991; Roche, Guo and
Moore, 1997). Size attained provides an indicator of growth status,
and if the individual is followed over time, an indicator of growth
rate (Kuczmarski et al., 2000). Generally, however, corresponding
data for other body dimensions are very limited (Walker, 1979;
Johnson et al., 1981; Roche et al., 1987; WHO, 1995). Most body
dimensions, however, with the exception of subcutaneous adipose
tissue and dimensions of the head and face, tend to follow the same
pattern of growth as height and weight
(Bloom, 1964; Tanner and Whitehouse, 1982), whereas body
proportions show different patterns (Roche and Malina, 1983;
Schmidt-Nielsen, 1984). The evaluation of growth status requires
reference data or growth charts (WHO, 1995). The new growth charts
for United States children and adolescents developed in 2000 by the
National Center for Health Statistics (NCHS) in collaboration with
Centers for Disease Control and Prevention (CDC) have become norm
reference worldwide (Roche et al., 1996; Roche, 1999; Kuczmarski et
al., 2000; Roche and Guo, 2001; Ogden et al., 2002) and now include
BMI-for-age percentiles for boys and girls from age 2 to 20 years
of age (CDC, 2000). The evidence from these data suggests that
height and weight are rather stable (i.e. they track well across
childhood and adolescence), although low tracking of stature is
observed at adolescence when height velocity is high. BMI curves
show that most changes have their origin during the first years of
life. The BMI also tracks well but interpretation of the BMI as an
indicator of fatness in children and adolescent needs caution due
to inconsistencies (Rolland-Cachera et al., 1987; Rolland-Cachera
1993; Siervogel, 1991; Guo et al., 1994; Power et al., 1997; Dietz
and Robinson, 1998; Cole et al., 2000). Nutrition affects fatness
and stature, but the consequences of under- and over-nutrition
differ between early childhood and adolescence. The growth of
individual children tends to remain at or near certain percentile
levels on reference charts after about 2 or 3 years of age until
adolescence (Cameron, 1984, 1991, 1992). However, before this
period, percentile levels of individual children often change.
Shifts usually occur between adjacent channels or percentiles on
the growth chart but may occasionally cross two or more percentile
lines. Such a shift in longitudinal data is known as decanalization
(Roche and Li, 1998). Decanalization,
common in infancy and early childhood, is of no concern in the
absence of disease and, commonly, is a gradual expression of the
childs genetic potential for height. To some extent body
composition reflects nutritional status. It is also influenced by
age, sex, race, physical activity and disease. The method used to
measure body composition depends on the variable to be quantified.
It may also depend on the practical conditions of the study
(Rolland-Cachera, 1993). Detailed methods, such as densitometry,
isotope dilution (neutron activation), bioelectrical impedance
(BIA) and dual-energy x-ray absorptiometry (DEXA) give more
accurate information, but they are commonly based on hypotheses
established in adults. Anthropometric measurements can be used
directly or as ratio or regression equations. At adolescence, the
body mass index (BMI) is preferred to weight for height as age is
taken into account. In addition, the BMI pattern reflects real
changes in body shape, and early in life it is an indicator of
later development. In addition to measuring weight and height,
skinfold measurement is usually carried out. The triceps skinfold
is usually recommended and widely used as it is better than the
subscapular skinfold to predict percent body fat, although some of
the popular algorithms factorize the two skinfolds. Trunk
skinfolds, such as the subscapular, iliac crest, supraspinale and
abdominal are better than extremity skinfolds for their association
with internal fat and their good correlations with risk factors and
response to nutritional interventions. However, many authorities,
nowadays, prefer the sum of four to eight skinfolds taken directly
as a measure of body fat to percent fat because it eliminates the
problems arising from assumptions factorized into the derivation of
the equations. Body density (Db) declines in males from about 8 to
10 years but then increases more or less linearly to about 16 to 17
years of age. In females on the other hand, Db decreases
from about 8 to 11 years of age, then increases only slightly,
and finally reaches a plateau by about 14 years of age. Both sexes
also show a slight decline in Db in late adolescence and young
adulthood (Malina et al., 1988; Malina, 1989). The results of
pooled samples taken from Japanese adolescent children 11 to 18
years of age grouped by age and sex are consistent with that for
American adolescents (Tahara et al., 2002). The accurate
application of the principles and methods for estimating body
composition to children requires that a determination be made as to
when, during growth, adult values for the primary components of the
fat-free mass are attained. This idea led to the development of the
concept of chemical maturity. Changes in the chemical composition
of the body during growth can be appreciated in a comparison of the
infant and young adult reference males (Brozek, 1963; Fomon, 1966;
Forbes, 1986). The point of chemical maturity, defined by Moulton
(1923) as the point at which the concentration of water, proteins
and mineral salts becomes comparatively constant in the fat-free
cell, does not occur until after puberty, but most changes occur
early in life. At present, chemical composition data for a young
adult reference female or for the years between infancy and
adulthood are not available (Forbes, 1987; Malina, Bouchard and
Bar-Or, 2004). However, presently available longitudinal data
suggests that the fat-free mass tracks moderately well from
childhood through adolescence in both sexes, whereas fat mass and
percent body fat are less stable characteristics (Fomon et al.
1982; Houtkooper et al. 1992; Guo et al. 1997; Tahara et al. 2002).
Tracking is the maintenance of an individual in the same percentile
range across age and varies according to the growth parameter and
to the period of growth. Low tracking of fatness (up to the age of
8 years) corresponds to the period of rapid chemical changes.
The accumulation of body fat and changes in the relative
distribution of fat, both subcutaneous and visceral, associated
with differential timing of sexual maturation, are implicated as
risk factors for overweight and/or obesity. Earlier studies
(Forbes, 1964; Cheek, 1970) as well as more recent efforts (Malina
and Bouchard, 1988; Malina et al., 1989, 1995; Beunen et al., 1994;
Kuczmarski et al., 2000) indicate that obese children are taller,
on the average, and more advanced in skeletal maturity compared
with non-obese children of the same chronological age. Males
accumulate proportionally more subcutaneous adipose tissue on the
trunk during adolescence compared with females. Although the exact
mechanism is not clear, hormonal factors have been implicated
(Horswill et al., 1997). A history of obesity during childhood and
adolescence also has implications, or consequences for adult
health. The increased prevalence of obesity among children and
adolescents has been accompanied by an increased prevalence of
obesity in adults in many countries throughout the world (WHO,
1998; British Nutrition Foundation 1999; Flegal and Troiano, 2000;
Flegal et al., 2002; Katzmarzyk, 2002a, 2002b). The age at
adiposity rebound has also been identified as a risk factor for
adult overweight/obesity (Rolland-Cachera, 1984, 1987, 1991).
Variation in the distribution of fat is a known risk factor in the
development of several diseases in adults, such as adult onset
dependent diabetes mellitus and cardiovascular diseases (Guo et
al., 1994; Gutin and Barbeau, 2000). However, studies done on
African populations are sparsely reported (Steyn, Joubert and
Roussouw, 1990). In addition to hormonal factors, intraindividual
and interindividual differences in the profile of fat deposition
have been associated with the metabolic properties of the
adipocytes (fat-secreting cells). The traditional view of the
adipose cell was one in which
the cell provided a storage structure for fatty acids in the
form of triacylglycerol molecules and for the release of fatty
acids when metabolic fuel was needed. Of course fat cells are
responsible for these critical functions. However, the adipose cell
is now better appreciated as a complex organ whose functions are
not limited to storage of unneeded calories and delivery of
metabolic fuel in times of fasting or starvation or other kinds of
biological passivity. Its functions are now known to include the
regulation of energy balance, glucose and insulin metabolism, lipid
metabolism, immunity, feedback regulation of adipogenesis,
production of estrogens and the regulation of blood pressure
(Ailhaud and Hauner, 1998; Romanski et al., 2000; Fruhbeck et al.,
2001). The
reporting of the discovery of Leptin in 1994 has resulted in the
opening of an entirely new chapter in the biological sciences
(Zhang et al., 1994). The understanding that leptin, a
cytokine-like molecule synthesized and secreted by adipocytes in
proportion to fat mass in most people, is implicated in the
regulation of food intake, energy expenditure, glucose and lipid
metabolism, puberty, reproductive functions, angiogenesis, and
other processes is important (Masuzaki et al., 1997). New
technologies such as computerized tomography (CT) and magnetic
resonance imaging (MRI) now permit differentiation of subcutaneous
and visceral adipose tissue in the abdominal area, and a sex
difference in visceral adiposity appears to occur during late
adolescence when males accumulate proportionately more visceral
adipose than females (Bouchard, 1994; Goran, 1995, 1999; Huang et
al., 2001). Ratios of trunk and extremity skinfolds suggest that
subcutaneous fat distribution is not stable during childhood.
During growth, some fat individuals move away from the high fatness
categories, whereas some lean children move into these categories
(Katzmarzyk
et al., 1999; Campbell et al., 2001). However, few studies have
examined the stability of relative adipose tissue distribution from
childhood to adulthood.
Body dimensions and growth curves The course of growth in
stature and weight from birth to 19 years of age has been amply
illustrated as distance or size-attained curves (Kuczmarski et al.,
2000) and velocity curves (Tanner, Whitehouse and Takaishi, 1966)
in several authoritative texts, journal reports and growth charts
(Flegal et al., 2002; Malina, Bouchard and Bar-Or, 2004). Other
curves already generated are distance curves for body mass index
(RollandCachera et al., 1991) as well as growth patterns for other
body dimensions such as sitting height and leg lengths (Martorell
et al., 1988), biacromial and biiliocristal breadths (McCammon,
1970; Roche and Malina, 1983), distance curves for arm and calf
circumference (Johnson et al., 1981). Ratios such as sitting height
as percentage of stature (Roche and Malina, 1983) and biiliocristal
to biacromial breadths (Roche and Malina, 1983) are also available.
Percentile curves useful in evaluating the growth status of
individual children have been developed and revised since the late
1950s in the United States (U.S.) as the National Health
Examination Survey (NHES, 1959-1970), National Health and Nutrition
Examination Survey (NHANES, 1971-2000), and Hispanic Health and
Nutrition Examination Survey (HHANES, 1982-1984). Some of these
data have been incorporated into these percentile growth charts
developed and also revised by the U.S. Center for Disease Control
and Prevention (CDC Growth Charts 1973, 1988 and 2000). The curves
represent age-specific and sex-specific averages for boys and girls
and do not
portray the wide range of normal individual variability apparent
in any group of children. The pattern of changes is generally
similar in all children, but the size attained at a given age and
the timing of the adolescent growth spurt varies considerably from
child to child. From birth to early adulthood, both stature and
weight follow a four-phase growth pattern: 1) rapid gain in infancy
and early childhood, 2) rather steady gain during middle childhood,
3) rapid gain during the adolescent spurt, and 4) slow increase
until growth ceases with the attainment of adult stature
(Kuczmarski et al., 2000). Body weight, however, usually continues
to increase into adult life. Adolescence is a difficult period to
define in terms of chronological age because of the variation in
the time of its onset and termination. The World Health
Organization (WHO) defines the age of adolescence as between 10 and
18 years, but the age ranges 8 to 19 years in girls and 10 and 22
years in boys are more appropriate as limits for normal variation
in the onset and termination of adolescence. In this period, most
bodily systems become adult both structurally and functionally,
i.e. they reach maturity. Structurally, adolescence commences with
acceleration in the rate of growth in stature, which marks the
onset of the adolescent growth spurt. The rate of growth in height
reaches a peak, then begins a slower or decelerative phase, and
finally terminates with the attainment of adult stature.
Functionally, adolescence is usually viewed in terms of sexual
maturity, which actually begins with changes in the neuroendocrine
system before overt physical changes and terminates with the
attainment of mature reproductive function. From a biological
perspective, the period of adolescence includes two major events,
the adolescent growth spurt (somatic maturation) and sexual
maturation. Youth enter this phase of growth at varying ages
(differential timing) and proceed through it at variable
rates (differential tempo). Timing and tempo are highly
individual characteristics and are unrelated. Girls are, on
average, in advance of boys in the timing of maturation, but
tem