Baxter-Jones, Adam D. G. Ph.D.*; Thompson, Angela M. Ph.D.†; Malina, Robert M. Ph.D., F.A.C.S.M‡
Section Editor(s): Maffulli, Nicola M.D.
In recent years, reports of potentially harmful effects of intensive physical training beginning at young ages on the growing female athlete have alarmed parents, coaches, sport administrators, sports medicine practitioners, and the broader public. The primary concern is that training may delay pubertal growth and maturation. On the other hand, there have also been claims of positive influences of intensive training for sport on the growing and maturing athlete. There is considerable interest in identifying physical characteristics associated with success in several sports, e.g., gymnastics, figure skating, and ballet, and then identifying these characteristics at an early age in children who may have potential for success.
To examine the effects of sports participation on a young girl's subsequent growth and maturation, it is important first to review the concepts of somatic growth and sexual maturation in the healthy child.
GROWTH, MATURATION, AND DEVELOPMENT
Children experience three interacting processes: growth, maturation, and development. Often, these terms are treated as the same; yet, these terms refer to three distinct processes that occur in the daily lives of children and youth for approximately the first two decades of life. 1
Growth refers specifically to the increase in the size of the body as a whole, and of its parts. Thus, as girls grow, they become taller and heavier, they increase in lean and fat tissues, their organs increase in size, and so on. Different parts of the body grow at different rates and times. For example, in healthy girls, heart volume and mass follow a growth pattern similar to body weight, whereas lung size and bone mass grow in proportion to height. The different rates and timing of growth in the body and its parts results in changes in body proportions—that is, the relationship of one part of the body to another. The legs, for example, grow faster than the trunk during childhood; hence, the child becomes relatively longer-legged.
Maturation refers to progress towards the biologically mature state. It is an operational concept, because the mature state varies with body systems. Maturation differs from growth in that although various biologic systems mature at different rates, all persons reach the same endpoint and become fully mature. In contrast, there are wide variations in endpoints of growth, such as adult stature and physique.
Maturation—that is, the process of maturing—has two components: timing and tempo. Timing refers to the time when specific maturational events occur: age when menarche is attained, age at the beginning of breast development, age at the appearance of pubic hair, or age at maximum growth during the adolescent growth spurt. Tempo refers to the rate at which maturation progresses—how quickly or slowly a person passes from initial stages of sexual maturation to the mature state. Timing and tempo vary among individuals. Studies of growing children commonly focus on sexual and skeletal maturation.
Development refers to the acquisition of behavioral competence—the learning of appropriate behaviors expected by society. It is culture-specific. As children experience life at home, school, church, sports, recreation, and other community settings, they develop cognitively, socially, emotionally, morally, and so on. Children and adolescents learn to behave in culturally appropriate manners.
It is important to recognize that the three processes—growth, maturation, and development—occur simultaneously and interact. Growth and maturation are characterized by individual variation and, although under genetic and neuroendocrine control, environmental factors may also have an influence. 1–3 Physical activity, especially intensive training for sport, is often indicated as one such environmental factor. The demands of specific sports are superimposed upon those associated with normal growth, maturation, and development. Although widely discussed and, to a lesser extent, systematically investigated, the exact role of regular training is yet to be determined. Nevertheless, there is concern about potentially negative influences of intensive training on the growth and maturation of élite young female athletes in some sports. 4,5
Assessment of Growth
Assessing the longitudinal growth of an individual child is a dynamic statement of the general health of that child. Measurements should be performed often and accurately to detect alterations from expected growth. Although a single point on a growth chart is not informative, several points plotted over time illustrate whether a person's growth is average, a variant of the norm, or abnormal.
Stature (height) and body mass (weight) are the two body dimensions most commonly used to monitor growth. With age, girls are expected to become taller and heavier. Growth status (size attained at a given age) and progress (rate of growth) are usually monitored by making comparisons with reference percentiles, where the 50th percentile (P50) represents the average size at any given chronologic age. 6,7 Reference percentiles or standards are based on cross-sectional data derived from large, representative samples of children from infancy to young adulthood. Such charts are useful for the comparison or assessment of growth status of a child or a sample of children, at a given age or across several ages. However, since growth rates are not linear during childhood and adolescence, the interpretation of these comparisons or assessments may be difficult at times.
Assessment of Maturation
Biologic maturation differs fundamentally from the measurement of growth in that every child reaches the same endpoint by becoming fully mature. Yet, the processes of growth and maturation are intimately linked as differential growth creates form. As stated previously, maturation refers to the timing and tempo (rate) of progress from prepubertal childhood to adulthood. It is most often viewed in the context of skeletal (skeletal age), sexual (secondary sex characteristics), and somatic (age at peak height velocity) maturation. 1,8,9
It is imperative to assess maturity or biologic age in the study of growth. Chronologic age is of limited utility in the assessment of maturity. Other methods of assessment are necessary. Although existing methodology provides the required mechanism to assess maturity, there are limitations to the available methodologies. 10 Skeletal age assessment is the single best maturational index, but it is costly, requires specialized equipment and interpretation, and incurs radiation safety issues. Several different methods are available to assess the skeletal maturity of the hand and wrist. However, these different methods do not provide equivalent estimates of maturation. 1 Although the methodology of skeletal age assessment covers the entire period of growth from birth to maturity, a further disadvantage is that it does not lend itself to field work. Dental age and morphologic age are broader measurement techniques for maturation with limited applicability. Somatic methods such as age of peak height velocity (PHV), or the differential rates of growth associated with regional growth, require serial measurements for a number of years surrounding the occurrence of peak velocity; as a result, they are not suitable to assess maturation in a one-time measurement of growth. This is another important consideration, because many studies of young athletes are short-term, and rarely span the entire period of the adolescent spurt.
Other alternative noninvasive assessments of biologic maturity include predicting adult stature from somatic dimensions and chronologic age from a one-time measurement of growth (the Beunen-Malina prediction), and then using percentage adult stature as a maturity indicator. 11 Recently, Mirwald et al. 12 suggested using the known changes in body proportions associated with maturation to predict age at PHV, again from a one-time measurement of growth, and then using age from PHV as a maturity indicator.
However, the most obvious feature of biologic maturity during adolescence is sexual maturation. The first overt sign of sexual maturation in girls is usually the initial development of the breasts, followed by the appearance of pubic hair. Each of these secondary sex characteristics goes through a series of changes as the girl passes through puberty to maturity. 1,2 These characteristics are usually assessed at clinical examination, although self-administered scales have been used frequently in the sport and exercise literature. 8 Clinical assessment of secondary sex characteristics requires invasion of the adolescent's privacy at a time of life when the youngster is learning to cope with the physiologic changes that are occurring. Hence, monitoring these characteristics requires utmost care and sensitivity to the youngster involved. Since only five discrete stages have been identified, a disadvantage of assessing them is that only an approximate classification of maturity occurs. Continuous measure from a fixed milestone, such as PHV or menarche, provides a continuous and probably more accurate indicator of biologic maturity.
One sexual milestone that is easily assessed is menarche, the first menstrual period. Menarcheal status (i.e., whether menarche has or has not occurred) and chronologic age at menarche in individual girls can be obtained from a careful and sensitive interview. At times, it may be more appropriate to interview the girl's mother to obtain this information. In addition, familial effects can be investigated by obtaining information with regard to the mother's age of menarche. 13,14
Normal Variance of Growth
Size at birth is determined largely by genetic potential and intrauterine environment. Linear growth velocity rapidly decelerates from birth to 2 years (approximately 9 cm per year) and from 2 years to 5 years (approximately 7 cm per year). Linear growth then continues, on average, at approximately 5 cm to 8 cm per year until the onset of puberty (the terms “puberty” and “adolescence” are used interchangeably). By approximately 9 to 10 years in girls and 11 to 12 years in boys, the rate of growth in height begins to increase. This point of acceleration in the rate of growth in height marks the beginning of the adolescent growth spurt, a period of rapid growth that is highly variable among individuals. The rate of growth increases until it reaches a peak (PHV); then, it gradually decreases, and growth in height eventually ceases. Girls, on average, start their growth spurt, reach PHV, and stop growing about 2 years earlier than boys. Nevertheless, when the growth spurt starts, when PHV is reached, and when growth stops are quite variable among individuals.
Statural gain from birth to adulthood can be viewed as a form of motion, in which the increase in height between these two time periods is the distance traveled, and height gain per year represents the speed of the journey. The rate of growth, therefore, reflects the child's state at any particular time better than the distance achieved or size attained.
The growth spurt in body mass begins slightly later than the growth spurt in stature. Body mass is a composite measure of many body tissues. It is most often partitioned in terms of lean (fat-free) and fat components. Thus, body mass = fat-free mass (FFM) + fat mass (FM). The growth pattern of FFM is similar to that of body mass, and a clear adolescent growth spurt is evident. Fat mass increases more gradually during childhood and adolescence.
The normal range of variation for the occurrence of menarche is 9 years through 17 years of age. Estimated median ages at menarche for European girls from the mid-1960s through the 1980s ranged between 12.5 years and 13.5 years, while the estimate for United States girls is 12.8 years. 15
Sexual maturation is accompanied by small gains in muscle mass and strength, a widening of the hips relative to the shoulders, and substantial gains in fatness. In girls, sexual maturation also influences behavioral development: increased self-consciousness about overt manifestations of sexual maturation, concern with weight gain, relationships with the opposite sex, and so on.
GROWTH AND MATURITY STATUS OF YOUNG ATHLETES
A number of difficulties in assessing the growth and maturation of young athletes should be kept in mind. The first factor to consider is the definition of an athlete. Often, the definition of what constitutes a young athlete is vague, including a wide variety of age groups, skill, and competitive levels. Many studies of young athletes, however, include youth who can be classified as select, élite, or junior national caliber. 16 Typically, young athletes are a highly select group with regard to skill and performance levels. Size, physique, and other environmental factors likely interact with skill and performance.
Body Size of Young Athletes
On average, young female athletes from most sports have statures that equal or exceed the median (P50) from reference standards from childhood through adolescence. It has been found that female basketball players, volleyball players, tennis players and swimmers have mean statures, from 10 years of age onwards, that were above the 50th percentile of the reference populations. 16 The same finding has been observed in élite female junior rowers. 17 In contrast, gymnasts consistently present profiles of short stature, with mean values below the 50th percentile. A secular trend for decreased stature in gymnasts has been observed. Today's élite female gymnasts are, on average, shorter than the gymnasts of 20 years ago. 18 Figure skaters of both sexes also present shorter statures, on average, though data are not extensive. Female ballet dancers tend to have shorter statures during childhood and early adolescence, but catch up to nondancers in late adolescence. 16
Body mass presents a similar pattern, with several exceptions. On average, young athletes in a variety of sports tend to have body masses that equal or exceed the reference medians. Gymnasts, figure skaters, and ballet dancers of both sexes consistently show lighter body mass. Gymnasts and figure skaters have appropriate mass-for-height, while ballet dancers have low mass-for-height. A similar trend for low mass-for-height is indicated in female distance runners. Although female athletes from a number of sports tend to be heavier than reference populations, they also, in general, have lower skinfold thicknesses.
Physique of Young Athletes
Physique is often a selective factor in sport. Physique, or body build, refers to the configuration of the entire body, as opposed to emphasis on specific features. Assessment of physique focuses on external dimensions and characteristics of the body. It is most often quantified as somatotype, which is defined by the contributions of endomorphy (roundness of contours, fatness), mesomorphy (dominance of muscular and skeletal development), and ectomorphy (linearity). The three components together describe an person's physique. It is inappropriate to consider a component of somatotype independent of the other two components, or without statistically controlling for the other two components.
In general, late adolescence is a period of decline in physical activity, and at the same time, a period when many adolescent girls indicate a desire to be thinner. In a study that considered the relationship between physique and motivation for sport (410 Portuguese girls aged 16–18 years), it was found that girls with somatotypes at the outer limits tended to show low scores with regard to motivation for sport. 19
Athletes in a particular sport tend to have reasonably similar somatotypes and exhibit a limited range of variability, compared to the general population. 20 With the exception of the throwing events in track and field, the higher weight categories in weight lifting, and related activities, endomorphy is rather low in most athletes, mesomorphy is well developed, and there is more variability in ectomorphy. Data for early adolescent and adolescent athletes (about 12–18 years of age) suggest that successful athletes tend to have, on average, somatotypes similar to adult athletes in their respective sports. 20,21 Similar to adult athletes, there is typically less somatotype variation among younger athletes, compared to the general population. Compared to adult athletes, young athletes tend to be less endomorphic (particularly females), less mesomorphic, and more ectomorphic. The latter component, of course, reflects the role of growth in the transition from late adolescence into young adulthood.
Physique is a significant contributor to success in many sports and may be of particular importance in aesthetic sports. Performance scores in subjectively evaluated sports, such as gymnastics, figure skating, and diving, may be influenced by the athlete's physique as perceived by the judges. For example, in a sample of élite gymnasts participating in the 1987 World Championships Artistic Gymnastics (Rotterdam), about 41% of the variance in the total competition score could be explained by endomorphy (negative coefficient) and chronologic age (positive coefficient). 22 The positive influence of chronologic age suggests an important role for experience in international competition. On the other hand, the negative effect of endomorphy is difficult to explain. It may reflect a real influence of endomorphy on performance, a negative perception of endomorphy by the judges, or some combination of the two factors. Mean endomorphy scores ranged from 1.4 to 1.9 in this international sample of élite gymnasts. This range of scores was uniformly low and homogeneous across the ages (13–20 years) examined, 23 which markedly contrasts with the trend toward increasing endomorphy with age across adolescence in nonathlete females. In a national sample of Flemish girls, the mean endomorphy scores increased from 2.9 at 10 years of age to 4.1 at 18 years of age. Thus, it may be difficult to detect a negative influence of such low endomorphy on competition scores.
A similar trend was observed in élite young divers. For a sample of 121 male and 151 female Junior Olympic divers from 11 to 18 years of age observed in 1991 and 1992, 12 males and 17 females were identified as successful in future national and international competitions. As youths, the successful female divers were more muscular (greater estimated arm and calf muscle circumferences), and had less relative fatness and lower endomorphy scores than those who were not successful. Female divers, as a group, are higher in endomorphy scores than gymnasts, with mean values ranging from 2.5 to 3.5 among divers 11 to 18 years of age. 21
The issue of the perception of fatness or endomorphy by gymnastics judges, or the aesthetic demands of the sport which place an emphasis on petiteness and leanness, should be systematically addressed. This point has relevance for the health of young athletes, particularly gymnasts, many of whom are in negative energy balance in an attempt to limit weight gain and fat accumulation, when the normal course of growth and especially sexual maturation is to gain in both. Undue emphasis on leanness can potentially have a negative influence on the health of young athletes, in particular girls. The same applies to other sports in which coaches or the sport system place undue emphasis on fatness in female athletes, such as distance running, ballet, and swimming.
Maturation of Young Athletes
Except for the age at menarche, data on the maturity status and progress of young female athletes is limited. Maturity differences among young female athletes are most apparent during the transition from childhood to adolescence, particularly the adolescent growth spurt, which reflects the individuality in timing and tempo of maturation. Data on skeletal age are mostly available for female gymnasts and swimmers, with less data available for ballet dancers and track athletes. The data for track and field athletes are to some extent confounded as they differ according to type of event.
During childhood, gymnasts have skeletal ages that can be classified as average or on time for chronologic age. As gymnasts span the age range of puberty, most gymnasts are classified as average and late-maturing, with few early-maturing girls in the samples. In later adolescence, most gymnasts are late-maturing. 16 These data suggest that early- and average-maturing girls are systematically represented less among gymnasts as girls pass from childhood through adolescence. This trend probably reflects the selection criteria of the sport, and perhaps the performance advantage of later-maturing girls in gymnastics activities. Corresponding data for secondary sex characteristics are less extensive, but are consistent with the trends observed in skeletal age. Although data are not as extensive as for gymnasts, female ballet dancers and distance runners show a similar maturity gradient in adolescence. In contrast, female swimmers tend to have skeletal ages that are average or advanced in childhood and adolescence. 5,16 The data for later adolescence in swimmers are difficult to evaluate, because maturity status for that age is influenced by early attainment of maturity by youth advanced in maturation, as well as the catch-up of average and later maturing youth. In other words, all youth eventually reach skeletal and sexual maturity.
Discussions of the biologic maturation of female athletes usually focus on menarche, which is a late pubertal event. There is confusion about the later ages of menarche in athletes, which is related to the methods of estimating age at which this indicator of maturity occurs. 8 Age at menarche can be estimated in three ways. Longitudinal studies use a prospective method of assessment. Specifically, girls are ordinarily examined at 3-month intervals, so that interviews with the girl or her mother on each occasion usually provide a reasonably accurate estimate of when menarche occurs. Sample sizes in prospective studies are generally small. Longitudinal studies of athletes followed from prepuberty through puberty are ordinarily short-term and limited to small, select samples; a potentially confounding issue of these studies is selective dropout.
Another way to estimate menarche is the status quo method. This method provides a sample or population estimate for the age at menarche. It is a statistical method (based on probits), which requires sample subjects who span approximately 9 years to 17 years in age. Two pieces of information are needed: the exact age of each girl, and whether she has attained menarche. Status quo data for young athletes actively involved in systematic training provides estimates for the sample, but these samples often include athletes of different skill levels and training histories.
The third method used to obtain the age of menarche is retrospective. Most data on the age at menarche of athletes are retrospective, and based on samples of postmenarcheal late adolescent and adult athletes. Retrospective data, of course, include potential errors associated with the accuracy of recall.
Menarche data for athletes in a variety of sports are summarized elsewhere. 5,9,24–26 Prospective and status quo data for gymnasts and ballet dancers, and status quo data for Junior Olympic divers and soccer players, are generally consistent with the retrospective data. The limited prospective and status quo data for tennis players, rowers, track athletes, and the more available data for age group swimmers, indicate earlier mean ages at menarche than retrospective estimates for each sport. In other words, it appears that late adolescent and young adult athletes (retrospective data) in these sports tend to attain menarche later than those involved in the respective sports during the pubertal years (prospective or status quo data). The differences probably represent the interaction of several factors, including the longer growth period associated with later maturation, selective success and persistence of late maturing girls in some sports, selective drop-out of early maturing girls, and increased opportunity in sport at the collegiate level or older ages.
DOES REGULAR TRAINING FOR SPORT INFLUENCE GROWTH AND MATURATION?
Over the last 100 years or so, many investigators have attempted to study the effect of systematic exercise or training on growth. Early discussions focused on a stimulatory or accelerating influence on growth, while more recent commentaries focus on a potentially negative influence of training on growth and maturation. Although early studies suggested that exercise increased the rate of growth, particularly in the height of males, the results were limited. The apparent acceleration in height observed in some studies was likely related to the earlier biologic maturation of the young male athletes studied, and to sampling variation, rather than the intensity of the training program. More recently, the literature examining the potential effects of training for sport on maturation has concentrated on female athletes, particularly the age at which menarche is attained. 13,14,27
Physical activity is not the same as regular training. Physical activity refers to the complex set of behaviors which encompass any body movement, produced by skeletal muscles, which result in energy expenditure above resting level. 28 Training refers to the systematic, specialized practice for a specific sport or sport discipline for most of the year, or to specific short-term experimental programs. Training programs are ordinarily specific (e.g., endurance running, strength training, sport skill training), and vary in intensity and duration.
Body Size and Regular Training
Sport participation and training for sport have no apparent effect on growth in height or the rate of growth in height in healthy, adequately nourished children and adolescents. With few exceptions, athletes of both sexes in a variety of sports have, on average, heights that equal or exceed data for nonathletes. Exceptions among athletes are gymnasts and figure skaters, participants in sports in which successful athletes present shorter heights than average. This trend probably reflects the selection criteria of these sports. The smaller size of élite gymnasts is evident long before any systematic training is started, 29 and is in part familial—i.e., gymnasts have parents who are shorter than average. 30 When parental stature was used to predict adult target height in a group of male gymnasts, swimmers, soccer and tennis players, it was found that gymnasts had significantly lower target heights than athletes in the other sports. 31 There is also a size difference between those who persist in the sport and those who drop out, who tend to be the taller individuals. 30,32 Corresponding data are not available for female figure skaters, but given the emphasis on early entry into this sport, one might expect similar trends.
In several sports in which the same youngsters are followed on a regular basis over time (volleyball, diving, distance running, basketball), short-term longitudinal studies of athletes indicate rates of growth in height that, on average, closely approximate rates observed in nonathletic children and adolescents. 16 The growth rates observed were within the range of normally expected variation among youth. In a recent study investigating the interactions between club-level sports training for gymnasts, figure skaters, and runners, compared with controls, it was found that club-level sports training did not affect growth or maturation during puberty. 33 Other recent studies investigating anthropometric variables related to competitive sports participation have also come to similar conclusions; that is, they do not find any links between anthropometric variables and training. 34–38 The results of these studies support the hypothesis that variations in body size and form are already present in the female athletes before the cessation of systematic training.
However, others suggest an opposite view. The results from a short-term longitudinal study of 22 Swiss gymnasts, compared with 21 swimmers, suggested that gymnasts were failing to obtain full familial height. 39 However, decreasing predicted adult height during puberty is a characteristic of slow or late maturation, confirmed by the late onset of menarche in these subjects. 39 Other studies of gymnasts, over longer time periods, have also observed lags in adolescent growth, but then reported subsequent catch-up growth. 4,32 Lindholm et al. 40 found that 6 out of 21 Swedish gymnasts, studied over a 5-year period, ended up 3.5 cm to 7.5 cm shorter than their predicted adult stature. Final height was predicted from parental heights. 41 Although this protocol gives a target adult height, one would expect 95% of daughters to fall within a 9 cm range of this value. 41 Thus, the final heights of these Swedish gymnasts are, in fact, well within the range of variation expected with the stature prediction method used. 40
In contrast to height, body mass can be influenced by regular training for sport, resulting in changes in body composition. Training is associated with a decrease in fatness in both sexes, and occasionally with an increase in fat-free mass, especially in boys. Young athletes also have thinner skinfold thickness than reference samples. It should be noted that individual skinfolds change differentially during growth. The differential growth of skinfolds is especially evident in boys. In boys, skinfolds on the extremities generally decline during adolescence, whereas trunk skinfolds do not show this decline. This trunk–extremity skinfold contrast is not as apparent in girls, although some extremity skinfolds may show a reduced rate of adipose tissue accumulation during adolescence. Maintenance of reduced levels of fatness depends on continued, regular activity or training (or caloric restriction, which often occurs in sports such as gymnastics, ballet, figure skating, and diving, for girls, and wrestling for boys). When training is significantly reduced, fat tends to accumulate.
It is difficult to separate specific effects of training on fat-free mass from expected changes that occur with normal growth and sexual maturation during adolescence. On the other hand, regular training during childhood and adolescence is associated with increased bone mineral content and mass. The beneficial effects of training on bone growth are more apparent in weight-bearing (e.g., running, soccer, gymnastics) than nonweight-bearing (e.g., swimming) activities. Of particular importance to physical activity and the integrity of skeletal tissue is the observation that bone mineral levels established during childhood and adolescence may be an important determinant of bone mineral status in adulthood. 42
Physique and Regular Training
Information on the effects of regular sport training during childhood and adolescence on the female physique is limited. In a study of young adult female swimmers, small changes in endomorphy (decrease) and ectomorphy (increase) were observed, while mesomorphy remained virtually unchanged. Changes in somatotype components ranged between +1.5 and −1.0 units; the greatest changes occurred in endomorphy and ectomorphy. Mesomorphy did not change in most swimmers. 43 These results suggest limited, if any, changes in somatotype with training in young women.
BIOLOGIC MATURATION AND REGULAR TRAINING
Does regular training for and participation in sport influence the timing and tempo of biologic maturation? As noted earlier, there is a wide range of normal variation among youth in the timing and tempo of biologic maturation. It is a highly individual characteristic that often shows a tendency to run in families; i.e., mothers and their daughters may both be early or late maturing. The following summarizes the general trends in the literature for young athletes.
Skeletal Maturation and Regular Training
Short-term longitudinal studies of girls in several sports indicated similar gains in skeletal maturation in both athletes and nonathletes. On average, skeletal age proceeds in concert with a child's chronologic age. 16 It should be noted that in later adolescence, differences in maturity status among participants at younger ages are reduced and eventually eliminated as skeletal maturity is attained by all individuals. A recent cross-sectional study of élite German gymnasts found, on average, a delay in skeletal maturity of 1.7 years. Although the authors suggest that intensive training combined with inadequate nutritional intake can alter pubertal development, the study is unable to distinguish the effects of training from those of normal variance in growth and maturation. 44
Somatic Maturation and Regular Training
Available data indicated no effect of training for sport on the age at PHV and growth rate of height during the adolescent spurt in boys and girls. 16 It has been suggested that intensive training may delay the timing of the growth spurt and stunt the growth spurt in female gymnasts. Unfortunately, the data are insufficient to warrant such a conclusion. Many confounding factors are not considered, especially the rigorous selection criteria for gymnastics, marginal diets, short parents, and so on. Female gymnasts, as a group, show the growth and maturation characteristics of short, normal, slow-maturing children with short parents. 30 Interestingly, male gymnasts also present consistently short statures and late maturation, but these trends are not attributed to intensive training. 16,31
Sexual Maturation and Regular Training
Longitudinal data on the sexual maturation of girls who are regularly active or training for sport are not extensive. The available data are largely cross-sectional, so it is difficult to make clear statements on potential effects of training for sport. The limited longitudinal data for girls active in sport compared to nonathletic girls indicated no effect of training on the timing and progress of breast and pubic hair development. Mean intervals for progression from one stage to the next, or across two stages of secondary sex characteristics, are similar for active and nonactive youth, and are well within the range of normal variation in longitudinal studies of nonathletes. 45 The interval between ages at peak height velocity and menarche for girls active in sport and nonactive girls also does not differ. This interval (1.2–1.5 years) is similar to those for several samples of nonathletic girls. 35
Most discussions of the potential influence of training on sexual maturation focused on the later mean age at menarche, which was often observed in female athletes. Typically, training for sport was indicated as the factor responsible for the later mean age at menarche, with the inference that training delays menarcheal onset. Unfortunately, most studies of athletes do not consider other confounding factors known to influence menarche. For example, there is a familial tendency for later maturation in athletes. 14 Mothers of athletes in several other sports attained menarche later than mothers of nonathletes, and sisters of élite swimmers and university athletes attained menarche later than average. In addition, age at menarche in athletes varies with the number of children in the family. 25 Athletes from larger families attain menarche later than those from smaller families. Thus, allowing for the many factors known to influence menarche, it is exceedingly difficult to implicate sport training, per se, as the causative factor for later menarche in female athletes.
Training and Potential Growth Disorders
In the few young athletes who present problems related to growth and maturation, there is a need for more systematic and comprehensive evaluation. Factors other than sport training must be more closely scrutinized. In many cases of short stature, the shortness is largely familial—i.e., short children tend to have short parents. Shortness may be related to constitutionally late maturation, which may also be familial. In some sports, the growth of young athletes may be compromised by chronic marginal or poor nutritional status, to which coaches, parents, and the specific sport system may be significant contributors. Some young athletes also present clinical eating disorders. It is possible that intensive training for sport may interact with or be confounded by these factors and others, in the sport and home environments of the young athlete. Hence, the effect of physical training on growth and maturation may be difficult to extract.
As continually emphasized in the review, sport is extremely selective and exclusive at élite levels. Most community-based programs emphasize mass participation. Other programs have as their objective the identification and subsequent training of young athletes with potential for success in regional, national, or international competition. In these programs, the selection–exclusion process begins early and appears to be a closed one, excluding many children from entering sport at a later age.
Much time and effort has been spent trying to identify the particular physical and psychological characteristics that contribute to the selection and development of athletic talent. 46 The debate has often focused on the relative contributions of genetic, environmental, and social factors. From the research available, it would appear that training does not affect growth and maturation. It is more likely that young athletes select themselves, or are selected by coaches and sport systems, into their specific sports. This finding implies that, in general, sporting success in the young athlete has a large genetic component, and that the differences observed in growth and maturation between athletes and nonathletes are the result of nature rather than nurture. Genetic considerations in growth, maturation, and performance are discussed in more depth elsewhere. 3
The young, potentially talented athlete has to be introduced to her sport. A major limiting factor to organized sport participation is the availability of local resources, in particular human resources, in the form of adults to coach, supervise, and administer programs. Parental support, in terms of time and finance, is very important. In a study of young British athletes, parents played the main role in introducing children into sport. Furthermore, most of these parents participated in sport themselves when they were younger. 47 Similarly, among university athletes in the United States, parents were most often indicated as the primary persons responsible for getting them involved in sport, and most of these athletes had one or both parents involved in sport at the high school level or above.
Economic considerations are an additional factor. Young athletes often travel considerable distances to get to a training facility and are dependent on their parent(s) for transport. The cost of intensive training can be considerable, and in the most part is met almost exclusively by parents. 48 Systematic training in sports such as gymnastics, swimming, diving, tennis, and figure skating are often limited to private clubs and require a substantial economic investment by parents and possibly sponsors. Economic considerations are, therefore, likely to limit access to sports for children and adolescents in many countries.
The data presented in this review emphasizes that body size and physique are major constitutional factors in the selection of young female athletes into their sports. The presently available data for female athletes cannot substantiate causality between training and growth. Specifically, concerns have centered on the suggestion that intensive training causes growth retardation and pubertal delay in sports such as gymnastics. Again, the data currently available does not warrant the conclusion that gymnasts proceed through puberty without a normal growth spurt, leading to reduced adult stature. To clearly show that intensive training is a factor, future studies should partition constitutional factors and the other components of the female athlete's sport environment before causality can be established.
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Nicola Maffulli, M.D., Guest Editor
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