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Defining growth, maturation, and development
This is an excerpt from Growth, Maturation, Physical Activity, and Sport-3rd Edition by Robert M. Malina.
Growth refers to an increase in the size of the body as a whole and its parts. As children grow, body size increases and body composition changes. Different parts of the body grow at different rates and times, which results in changes in body proportions. Changes also occur in specific organs and related structures. Heart mass and volume follow a growth pattern like that for body weight, whereas the lungs and lung functions follow a growth pattern like that for height.
Changes in body size and composition are outcomes of three underlying cellular processes: (1) an increase in cell number, or hyperplasia; (2) an increase in cell size, or hypertrophy; and (3) an increase in intercellular substances, or accretion. Hyperplasia, hypertrophy, and accretion all occur during growth, but the predominance of one or another process varies with age and the tissue involved. For example, the number of neurons (brain cells) is established by midpregnancy, though hyperplasia of different types of nerve cells continues during the second half of pregnancy and into postnatal life. The number of muscle fibers is established shortly after birth; fibers subsequently grow primarily by hypertrophy. However, all three processes occur in the process of bone growth. These cellular processes are also involved in the process of biological maturation.
Maturation refers to the process of becoming mature—specifically, progress toward the biologically mature state. Maturation occurs in all organs and organ systems: enzymes, chemical composition, functions, shapes, and so on. Maturity thus varies with the biological system considered. Sexual maturity is fully functional reproductive capability. Skeletal maturity is a fully ossified adult skeleton. Maturation of the nervous and endocrine (neuroendocrine) systems is a major factor in regulating growth in general and especially sexual, skeletal, and somatic maturation during the interval spanning late childhood through adolescence, generally called the interval of the adolescent growth spurt and sexual maturation.
Maturation can be viewed in three contexts: status, timing, and tempo. Status refers to the stage of maturation at the time of observation—for example, maturation of the skeleton (skeletal age) or reproductive system (stage of development of secondary sex characteristics, pre- or postmenarche). Timing refers to the age at which specific maturational events occur—for example, the age at the appearance of secondary sex characteristics in girls and boys, age at menarche (first menstrual flow), or the age at maximum growth in height during the adolescent growth spurt. Tempo refers to the rate at which maturation progresses in specific systems. Children and adolescents of the same chronological age (CA) vary considerably in their state of maturation at the time of observation; the timing of specific maturational events and the tempo of maturation also vary considerably among individuals.
It should be evident that the biological processes of growth and maturation are closely related. The former focuses on size attained at a given point in time, whereas the latter focuses on progress (rate) in attaining adult size and maturity. The target is the adult state—maturity—and the processes imply progress toward this target from the moment of conception until maturity is attained. For example, two children of the same age may be the same height (i.e., may have attained the same level of growth), but they can be at quite different places on the path to adult size or maturity. One child may have attained 65% of his or her adult stature, the other 75%. The individuals eventually reach the adult state but do so at different times and ages.
The processes underlying growth and maturation are cellular. The study of growth and maturation, however, focuses on the measurement and observation of the outcomes of these processes (e.g., size attained or level of fatness, level of maturity, or the extent to which an individual has progressed to adulthood). The measurement and observation of growth and maturation are discussed in detail in specific chapters of the book.
Development is a term that is used in the context of both biology and behavior. Biologically speaking, development refers to the process of the differentiation and specialization of embryonic stem cells into different cell types, tissues, organs, and functional units. Full differentiation is attained with the onset of function in a particular tissue. This mainly occurs early in prenatal life when tissues and organ systems are being formed, and it is highly dependent on the activation and repression of genes or sets of genes that interact with hormones and nutrients in the prenatal environment. The development of specific body systems obviously continues after birth as the different systems are functionally refined.
The term development is also commonly used in the context of the acquisition of behavioral competence in a variety of interrelated domains as children grow up and adjust to the social and cultural environments into which they have been born and are subsequently reared. Development refers specifically to the acquisition and refinement of behaviors expected by society. Thus, it is common to speak of social, cognitive, emotional, and moral development as the individual personalities of children emerge within the context of the particular cultures into which they are born and reared.
Motor development is an important component of behavioral competence. It refers to the acquisition and refinement of proficiency in a variety of movement activities, beginning in infancy with, for example, rolling over, sitting up alone, and eventually walking alone. The development of proficiency in movement activities involves interactions between the maturation of the nervous and muscular systems (neuromuscular maturation) and specific movement behaviors that occur in the context of the home, nurseries, preschools, free play, and so on. The latter, of course, reflect the culture into which a child is born and reared. Motor development and motor performance are considered in separate chapters, and both are relevant to physical activity and sport.
The processes of physical growth, biological maturation, and behavioral development are summarized in table I.1. As infants, children, and adolescents grow and mature, they develop behavioral competence in a variety of domains. Children do not grow, mature, and develop in isolation. They do so in the context of life at home, school, the neighborhood, church, sports, recreation, and other community activities. These processes occur simultaneously and interact; vary during infancy, childhood, and adolescence; and influence the individual’s relationships with both peers and adults (parents, teachers, coaches, etc.). Growth, maturation, and development influence self-concept, self-esteem, and perceived competence.
Self-concept refers to the individual’s evaluations and perceptions of oneself, whereas self-esteem refers to the value or worth that the individual places on oneself. Self-concept and self-esteem influence the individual’s perceived competence in a variety of social domains and contexts, including physical activity and sport.
The development of self-concept and self-esteem is often overlooked in biological discussions of the physical growth and maturation of children and adolescents. Similarly, the influence of individual differences in growth and maturity status is often overlooked in discussions of behavioral development. It is important to recognize that behavioral development and biological growth and maturation do not occur in isolation; the processes do in fact interact. The interactions are especially apparent during the transition into adolescence, when there is considerable variability among individuals in the timing (when) and tempo (rate) of the growth spurt and sexual maturation. There may also be a temporal discrepancy between biological growth and maturation on the one hand and social, personal, and emotional development on the other. This asynchrony may in turn affect the development of self-concept and self-esteem. How youngsters cope, or learn to cope, with their sexual maturity or adolescent growth spurt may influence their behaviors. It is thus important to recognize that children and adolescents cannot be approached in an exclusively biological or exclusively behavioral manner.
A biocultural perspective that recognizes the interaction of biological and societal demands on the growing, maturing, and developing individual is thus essential. Growth and maturation are biological processes, whereas development is a broader concept that involves several behavioral domains. Biological growth and maturation do not proceed in isolation of the behavioral realm.
Although the focus of this text is the biological aspects of growth, maturation, physical performance, physical activity, and sport, it is important to recognize that both the biological and behavioral domains interact in shaping individuals as they progress from the immature state to the mature state, or from infancy through childhood and adolescence and into adulthood. Physical activity and performance are behaviors that are influenced by the biological characteristics of the individual. Organized youth sports, for example, emphasize both performance and activity, but the contexts of specific sports vary considerably and are largely influenced by adults (parents, coaches, league administrators, etc.). It should be reasonably clear, therefore, that no set of isolated phenomena describes the growth, maturation, and development of children and adolescents or their level of physical activity and performance.
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