Vinod Anand | 09 Aug 2013

A BRIEF VIEW OF THE GROWTH OF CHILDREN (Vinod Anand) LONGITUDINAL STUDIES In a longitudinal study a group of children is followed over a period of time. The same children are measured at successive periods. Growing, not merely growth accomplishment is measured. Data from individual children can be combined and recombined in many ways. For example all the girls who reach the menarche at age 12 can be put in one group and their growth compared with girls who reach the menarche at age 13. It is soon seen that age of menarche has far more significance for growth than chronological age. Longitudinal studies are more difficult to conduct than cross-sectional ones. It takes years to complete a study in which the investigator is waiting for his subjects to grow up; families move about, so it is difficult to maintain a group of children for a long span of years; longitudinal studies are expensive; and investigators as well as children grow older with the years! At the present time in the United States there are a number of large-scale longitudinal studies, some under way, others completed. The Brush Foundation Study of Child Health and Development in Cleveland, the Fels Research Institute Study of Prenatal and Postnatal Environment at Antioch, Longitudinal Studies of Child Health and Development of the Harvard School of Public Health in Boston, Studies of the Institute of Human Development in Berkeley, California, are some of the most outstanding studies. GENETIC INFLUENCES There are many genes which influence growth. Since it is of course impossible to identify them individually, the problem is to relate observable and measurable qualities of a child with his growth potential. Growth in childhood is correlated with (1) size at birth, (2) sex, (3) speed of maturation, and (4) body build, and perhaps with other factors, too. Of these four factors sex, with only rare exceptions, is readily observable at birth. It is certainly genetically determined, and there is no conceivable environmental factor which can change this basic fact about the individual. Birth weight is information easy enough to come by, but by itself it does not offer enough information to warrant prediction of growth. Body build and rate of maturing are probably genetically determined. Rate of maturing, while not determinable at birth, shows itself during the early years. Combined with sex and birth weight, it offers the best information for predicting what a given child should accomplish under good conditions. There is considerable evidence to suggest that although both body build and rate of maturing are genetically determined, they, unlike sex, may both be subject to change by environmental forces (see below). SIZE AT BIRTH The size at birth after full-term pregnancy is an index, although a rough one, of the ultimate size of the mature man. While dependent upon the genetic growth potential operating since conception, birth weight is influenced by many other factors. It is only a first step in estimating the growth potential of any given child. First-born infants are usually smaller by some ounces than later-born infants. Why this should be so is unknown, and there seems to be no correlation between this small difference and growth potential. Infants born to small women and fathered by large men are often smaller at birth than would be expected as judged by their ultimate growth (Tanner, 1956). Apparently some dampening effect from the mother keeps an infant in utero from becoming too large to pass through her small birth canal. Birth weight is related to duration of gestation. Lubchenco, Hansman, Dressler, and Boyd related birth weight to gestational age in a large series of premature and full-term infants. Their data suggest that infants destined to be large are already large by the end of 24 weeks of gestational age. SEX Boys and girls have different growth patterns. At birth boys are slightly bigger (between 1 and 4 per cent) than girls in both height and weight. During the first year of life boys grow slightly faster than girls, but between the ages of 1 and 9 the growth rate differences between boys and girls are almost nonexistent. At puberty the first significant differences in height and weight between the sexes become evident. It is at this time that the different endocrines exercise their effects—androgens in the male and estrogens in the female. Girls mature earlier than boys, so that for a few years the girls in any population group are larger than the boys in almost all dimensions. Then the boys begin their pubertal spurt; they catch up and pass the girls and end up roughly 10 per cent bigger. SPEED OF MATURING Some children progress along their predetermined growth pattern at a faster rate than others. The age at which a child matures sexually is a milestone that is convenient to use as a peg. Some girls accomplish sexual maturity in eleven years from birth; others take 16 or even 17 years to reach the same level of maturity. Boys are not as speedy as girls. The speediest can reach manhood in 12 years; the slow ones may take 18 years. Early maturers are early in all their physiologic accomplishments (Reed and Stuart, 1959). In general, during childhood they are taller and heavier than later maturers. Their skeletons grow faster, they get their teeth earlier, and they develop muscular capacity and coordination a little sooner than the late maturers. The speed of maturation is a gene-determined phenomenon. The early maturers become adults who have more weight for height than late maturers. BODY BUILD Adult human bodies vary in all their external dimensions. Almost all classifications consist of two extreme types and one intermediate one. At one extreme human beings are tall and thin, the typical Uncle Sam; at the other extreme they are short and fat, the John Bull. In between there is the strong muscular athlete, the Hercules. Sheldon uses the terms endomorph, mesomorph, and ectomorph to describe the three types. The endomorph has a round head and large, fat abdomen predominating over this thorax. His arms and legs are short, with considerable fat in the upper arm and thigh but with slender wrists and ankles. He has a great deal of subcutaneous fat. His body is thick, his skeleton large. The endomorph is plump as a child and tends to put on weight as he gets older. The mesomorph is the strong athlete. Bone and muscle predominate, but he has much less fat than the endomorph. He has broad shoulders and chest and heavily muscled arms and legs with the lower segment strong in relation to the upper. The endomorph is the linear man; he has a thin, peaked face with a receding forehead, a thin, narrow chest and abdomen, spindly arms and legs. His muscles are neither large nor strong. He has very little subcutaneous fat. He seldom becomes obese. The majority of people have a moderate amount of each component in their somatotype. Virtually all somatotyping has been done on adults. In the Brush Foundation Growth Study a group that had been followed since childhood was somatotyped in early adult life. With the knowledge of their adult somatotypes their growth records were sorted out and recombined into groups of homogeneous somatotypes. The ectomorphs were taller than the mesomorphs at all ages from 4 onward, but the mesomorphs were heavier from age 2 onward. From the age of 2 the mesomorphs had more weight for height than the ectomorphs. Unfortunately somatotyping at the early ages has not at present been worked out. From longitudinal growth studies it was obvious, after the subjects reached adult size and could be somatotyped, that their growth in childhood varied according to the body build they finally achieved. This is important, but at present data are lacking with which to predict growth based on somatotype at birth. Bayley and Bayer (1946) have suggested another way of classifying body builds. They describe androgyny, the degree of masculinity in the female and femininity in the male. Androgyny emphasizes the fact that every individual has some characteristics of the opposite sex. Bayley and Bayer describe an undifferentiated pattern of body build characteristic of the neuter gender quality of early childhood. At puberty the pattern fans out either toward the hyperfeminine or the hypermasculine or remains intermediate (asexual). Some individuals travel all the way to the extreme of their sex; others stop part way, retaining elements of the undifferentiated pattern of childhood. While the final measurement of androgyny cannot be made until maturity is reached, nevertheless, like the somatotypes of Sheldon, the androgyny type is, Bayley and Bayer believe that an innate trait uniquely characteristic of the individual and possessed by him all his life. By means of certain anthropometric measurements during childhood these investigators have been able, at least roughly, to categorize children before puberty with respect to their androgyny scores. In the androgyny score considerable emphasis is placed on the distribution of subcutaneous fat and muscles. Women on the whole deposit more fat than men and men develop larger muscle mass than women. Amount of muscle and of fat are also factors in the somatotyping system of Sheldon. These two different methods of describing body build overlap. The mesomorph of Sheldon is the muscular type and is closely related to the hyper-masculine on the androgyny scale. As a male this type tends to mature early. The endomorph deposits an abundance of fat and is related to the hyper-feminine on the scale of Bayley and Bayer. As a female this type tends to mature early. The ectomorph of Sheldon, the linear person, is the asexual person of Bayley and Bayer; in both sexes they are late maturers. The muscular girl is high in mesomorphy on Sheldon’s scale, high in masculinity on that of Bayley and Bayer. Unlike the muscular boy, she tends to be a later maturers. The fat boy is high in endomorphy and high in femininity. He does not follow the early-maturing pattern of the endomorphic girl, he tends to be a late maturer. Brozek raises the question of how stable the body type of an individual remains through the life span. He feels that while there are stable (genetic) aspects to body build, the variable (environmental) aspects have been confused in most of the attempts to categorize body build. It is doubtless true that body build is not a simple, single, gene-directed characteristic. Body build is the result of the growth and development of the skeletal structure, the muscles, and the adipose tissue. Each of these parts of the organism is acted upon by many things, both intrinsic and extrinsic. Nevertheless there are measurable tendencies toward one or another of the recognized body types which are useful clinically.     PAGE  PAGE 1