characteristic of young athletes
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THE CHARACTERISTIC OF YOUNG ATHLETE
Introduction An implied plea is made for coaches to cease applying adult-relevant coaching practices to this population of athletes. It is obvious that the ways the body energizes activity and performs skilled movements in young people is different to those, which occur in adults. This issue does not touch on the psychological factors involved in this group of individuals even though they are distinctly different to those of adults. A case has been made to coach mature female athletes appropriately and differently to males. This particular issue may seem to promote a paradox to that principle. For practical purposes, pre-pubescent athletes can be trained without considering gender differences. While there are gender differences in children, they are relatively minor and small when compared to those existing in mature individuals. Adolescence is a time when gender differences appear. When they emerge depends largely upon the stage of maturation of individuals. Since females mature earlier than males, they warrant special attention to their unique characteristics and factors and the provision of gender-specific sport programs earlier than males. Developmental differences in adolescence make it particularly difficult to categorize specific coaching principles that can be applied in a manner that is similar in conceptual definition to that which is possible for children and adults. Young athletes are physically developing, from early childhood to late adolescence. This means they have different capabilities for, and adaptations to, exercise and for this
reason, young athlete training programs should not be just scaled down versions of adult training programs. More young people enjoy sports than ever before. Athletic participation has increased in grade schools, high schools and community programs. Young athletes have special needs. Because their bodies are growing, they often require different coaching, conditioning, and medical care than more mature athletes. It is important to examine the special requirements of young athletes to better prepare them for the competitive pressures and physical injuries that can come with increased sports activity. Statistics demonstrate the increased popularity of sports among young people. Fifty percent of boys and 25 percent of girls between the ages of eight and 16 compete in an organized sports program sometime during the year. Three-fourths of junior high schools and middle schools have competitive interscholastic sports programs. At the high school level, there are 32 male and 27 female competitive sports with 7,000,000 high school students participating. Beyond organized sports programs, millions more compete and participate in physical education classes, church and community intramural programs, and other recreational athletic activities. A host of factors has contributed to the awakening of interest in health, conditioning and sports. The media impact on youth has elevated talented college and professional athletes to heroic levels. The multimedia message on these sports heroes may confuse young athletes by creating unrealistic expectations. The early return to competition by
professional athletes following an injury creates the impression that athletes often heal faster than the rest of us. However, peer pressure and the economic and social forces exerted on school coaches to win may lead to decisions that are not truly in the best interests of a child's health, growth and development. The fastest rate of growth occurs in the first two years, the growth rate then slows until the adolescent spurt when the growth rate increases again. The adolescent spurt last approximately two years and takes place, on average, at 10 to 12 years for girls and 12 to 14 for boys. Growth rate then decreases until full height is reached. Muscle mass increases steadily until puberty, at which point boys show faster muscle growth. The hormonal changes at puberty also affect body composition in terms of fat. At birth, both boys and girls have around 10 to 12% body fat Pre-puberty, both girls and boys still have a similar 16 to 18% body fat Post-puberty, girls have around 25% body fat due to high serum oestrogen, which causes the hips to widen and extra fat to be stored in the same area. Post-puberty, boys have 12 to 14% body fat
There is a science of the child and the adolescent in exercise. It behooves all coaches to become familiar with the content and principles of those sciences so that maturing individuals can be provided with healthy and sound experiences in their sporting endeavors.
Young Athletes are Different The growing athlete is not merely a smaller version of the adult. There are marked differences in coordination, strength and stamina between a youth and an adult. In young athletes, bone-tendon-muscle units, growth areas within bones, and ligaments experience uneven growth patterns, leaving them susceptible to injury Increases in body size may be due to fat and not muscle, causing marked differences in strength. Too often unfair competition occurs between boys of 100 pounds of baby fat and peach fuzz versus 200 pounds of muscle and mustache. Grade school students are less likely to suffer from severe injury because they are smaller and slower than older athletes; when they collide or fall, the forces on their musculoskeletal system are usually not high enough to cause injury. On the other hand, high school athletes are bigger, faster, stronger and capable of delivering tremendous forces in contact sports. Coaches bear a prime responsibility in developing their young athletes and watching for early signs of physical problems (such as pain or limp). They often recognize severe injuries because their athletes show signs of pain and can't continue playing. Coaches may have more difficulty spotting less severe injuries, however, because the pain is low grade and the athlete often ignores it. Repeat injuries may turn into overuse conditions which can put the athlete on the sidelines for the rest of the season.
Many sports injuries in young athletes, particularly elbow and knee injuries are caused by excessive, repetitive stress on immature muscle-bone units. Such repetitive overuse can cause fractures, muscle tears or bone deformity Fortunately, such injuries are uncommon, and usually prolonged pain is an early warning sign. Coaches, parents and players should provide protection for the young athlete through proper conditioning, prompt treatment of injuries and rehabilitation programs. Conditioning programs usually strive to make the young athlete "physically fit" by improving muscle strength, endurance, flexibility, and cardio respiratory fitness. The coaches and parents also are responsible for creating a psychological atmosphere that fosters self-reliance, confidence, cooperation, trust and a positive self-image. Young athletes must learn to deal with success and defeat in order to place events in a proper perspective. Some coaches and parents go too far in analyzing player performance. The promotion of the "win at all costs" ethic has both short-term and long-term detrimental effects on impressionable young people. This issue is divided into four topics: children, adolescents, growth, and application criteria.
CHAPTER 1 THE GROWTH OF PHYSICAL CHARACTERISTICS IN MALE AND FEMALE CHILDREN
" . . . there is an increasing awareness and concern on the part of parents and educationalists about the possible harmful effects on children who participate at a progressively younger age and with ever-increasing intensity in sports competitions designed by and for adults." (Borms, J, 1986.)
Exercise and GrowthBoys and girls differ in stature. Girls experience their adolescent growth spurt and
peak height velocity on average about two years earlier than boys. The growth spurt of boys lasts longer and is somewhat more intensive than in girls. Subsequently, boys tend to catch up and then pass the growth period of girls. In any random sample, there is a remarkable range in body sizes in both sexes. Still tenable hypothesis : Epiphyseal growth may be stimulated by physical
activity to an optimal length but excessive and prolonged pressure can retard linear growth. There is no convincing evidence to support the view that regular and natural exercise promotes an increase in body size. 6
There have been no studies in children of effects of training on bone growth and its mineral contents although exercise does promote these factors (actually reverses demineralization) in adults.
Height and Bone
During the first two years of life there is a rapid increase in height, with 50 percent of adult height reached by the age of two years. This is followed during childhood by a progressive decline in the rate of change in height. Just prior to puberty, there is a marked increase in the rate of change in height, followed by an exponential decrease until full height is attained at a mean age of 161/2 years in girls and 18 years in boys. These trends are illustrated in Figure 1. There is a wide variation in the average age at which the different bones reach full growth or maturity, ranging from the preteens to the early twenties. On the average, girls achieve full maturity of their bones several years before boys. Exercise is regarded as essential for proper bone growth. While exercise appears to have little or no influence on the growth in length of long bones, it does increase the width of bone, gives the bone greater tensile strength, and lays down more mineral in the bone matrix.
Figure 1 : Changes in the rate of change in weight and height with age in both males and females between the ages of 6 months and 18 years
Figure 2 : Epiphyseal slippage at the proximal head of the femur in the left leg of an eight-year old girl injured while playing competitive soccer (from Murray Robertson, MD., Tucson, AZ ).
In this chapter, we are interested in the process of bone growth primarily for the purpose of understanding the potential for injury. An injury to an immature bone could
result in the premature cessation of growth, resulting in a shorter bone. Disruption of the growth of the femur, as an example, would lead to a difference in the lengths of the two legs, with the involved leg being much shorter. The greatest concern is with the potential for injury at the epiphyses, since a fracture at the epiphysis and growth plate could disturb the blood supply and disrupt the growth process. Fortunately, such injuries are relatively rare and seldom occur in sports. In one study of 31 epiphyseal injuries, only 23 percent were sports-induced, the remainder resulting from falls and vehicular accidents (Larson, 1974). Figure 2 illustrates a slipped epiphysis of the distal head of the femur in an eight-year old girl, whose presenting symptoms were initially diagnosed as a groin pull. The injury occurred during a championship soccer match.
Figure 3 :
An example of a separation of the epiphysis (Larson, 1974)
One type of serious epiphyseal injury that occurs in athletics is called traumatic epiphysitis. One form is "Little Leaguer's elbow," a condition resulting from repetitive strains to the medial epicondylar epiphysis of the humerus. According to Larson, studies have shown that 12-year-old boys can throw a baseball up to 70 mph. This can cause a
sudden pull on the epiphysis, which anchors the tendons of the involved muscles, which may result in its separation (see Figure 3). The repetitive stress of throwing may produce an inflammatory response, referred to as traumatic epiphysitis. In a well-controlled study published in 1965, Adams found epiphysitis by X-ray examination in all 80 pitchers in a group of 162 young boys, while only a small percentage of the nonpitchers and the control group of nonplayers exhibited similar changes. Subsequent studies have not substantiated this initial study, in that a much lower percentage of those with epiphysitis have been reported.
Larson and McMahan (1966) reviewed 1,338 consecutive athletic injuries seen by a group of four orthopedists in one major sports medicine practice. They reported that 20 percent of these injuries were in the age range of 14 years and younger. Only six percent of all injuries in 15-year-olds and younger involved the epiphysis. They also stated that this type of injury does not always result in crippling, or permanent, trauma and that early recognition is important.
Of all the sports, competitive baseball appears to be the most dangerous because of its potential for serious injuries, which largely result from the pitching motion. Some leagues have replaced the pitcher with a pitching machine. This would seem to be the only sensible approach until the youngster reaches an age at which pitching is not a major source of injury. Pop Warner football and the other competitive sports and activities have a relatively good record with regard to bone injury. While the potential for injury in football is generally considered high, apparently the small size of the player, the
matching of children by size, and good protective equipment provide a relatively safe environment for the young football player. Inappropriate equipment, and mismatching players by size and ability, creates an environment with a high potential for injury.
Muscle From birth through adolescence there is a steady increase in the muscle mass of the body that parallels the youngster's gain in weight. The total muscle mass in males increases from 25 percent of body weight at birth to 40 percent or more in the adult. Much of this gain occurs at puberty, when there is peak acceleration in the development of muscle, which corresponds to the sudden, approximately tenfold increase in testosterone production. Girls do not experience this period of rapid acceleration at puberty, but their muscle mass does continue to increase at a rate considerably below that of boys. Once a girl reaches puberty, her estrogen levels increase, which promotes the deposition of body fat. The increases in muscle mass with age appear to result primarily from hypertrophy of existing fibers, with little or no hyperplasia (increase in fiber number). The hypertrophy is the result of increases in the myofilaments and myofibrils. As bones grow in length, muscle length increases. Increases in the number of sarcomeres, which are added at the junction of muscle and tendon, and increases in the length of existing sarcomeres, result in this increase in muscle length. When the female reaches 16 to 18 years of age and the male 18 to 22 years, the muscle mass is at its peak, unless it is increased further through exercise, diet, or both. The muscle mass will remain relatively stable from this age through the ages of 30 to 40 years, if physical activity levels remain constant and do not decrease. With older age, there is a decrease in the total muscle mass,
which may result from both atrophy of selected muscle fibers, generally Type 11, and a decrease in the number of muscle fibers. The decrease in fibers may be the result of nerve fiber degeneration.
Fat Fat cells form and fat starts to deposit in these cells early in the development of the fetus and continues indefinitely. Each fat cell has the ability to increase in size at any age, from birth to death. Initial studies suggested that the number of fat cells became fixed early in life, thus it was considered important to keep the total fat content of the body low during this early period of development. In this way, the total number of fat cells would be minimized, and the chances of extreme obesity as an adult would be greatly reduced. More recent evidence, however, suggested that fat cells can continue to increase in number throughout life (Bjorntorp, 1986). The most recent evidence suggests that as fat is added to the body, existing fat cells continue to fill with fat to a certain critical level, at which point new cells are formed from pre adipocytes of undifferentiated cells. Thus, it is important to maintain good dietary and exercise habits throughout life!
Figure 4 : Changes in triceps and subscapular skinfold thickness (subcutaneous fat) with age, from 2 years to 18 years (data from the NHANES-I, National Center for Health Statistics)
The degree of fat accumulation with growth and aging will depend entirely on your dietary and exercise habits, in addition to heredity. While heredity is unchangeable, diet and exercise can be manipulated to either increase or decrease the fat stores. At birth, 10 to 12 percent of your body weight is fat, and by the time you reach physical maturity, the fat content reaches 15 to 25 percent of the total body weight for males and females, respectively. Figure 4 illustrates the relationship between subcutaneous fat at the triceps and subscapular sites, and age for males and females, with subcutaneous fat being representative of total body fat.
Nervous System As the child grows, he or she develops better agility and coordination, which is a direct function of the development of both the central and peripheral nervous systems. During the early stages of development, myelination of the nerve fibers must be completed before fast reactions and skilled movement can occur. Conduction velocity along a nerve fiber is considerably slower if myelination is absent or incomplete. Late in life, as aging progresses, conduction velocity along a nerve fiber may tend to slow. Speed of reaction and movement both decrease with aging due to an increased conduction velocity in the peripheral nervous system, both sensory and motor.
General Performance and Physiological Function. In almost all of the physiological systems, function appears to improve until
maturity, or shortly before, and then plateaus for a period of time, before starting to decline with old age. This section will focus on changes in motor ability, strength, cardiovascular function, aerobic capacity, and anaerobic capacity that accompany the growth and development process.
Motor Ability The motor skill ability of boys and girls generally increases with age, from six years to 17 years, although girls tend to plateau at about the age of puberty for most items tested. This is illustrated in Figure 5 . These improvements are the result of the development of the neuromuscular and endocrine systems that occur with growth and development, and secondarily to the increased activity patterns of these children. The plateau observed in the girls at puberty is most likely explained by two factors. With puberty, the increase in estrogen levels, or in the estrogen/testosterone ratio, leads to a greater deposition of body fat. As fat levels increase, performance tends to decrease. Probably of greater importance, however, is the fact that many girls assume a much more sedentary lifestyle coincident with puberty. As these girls become less active and more sedentary, their motor abilities tend to plateau.
Strength Changes in strength with age parallel the increases that occur in muscle mass. Peak strength is usually attained by the age of 20 years in females and between 20 and 30 years in males. Rather marked increases in strength occur at the time of puberty in the male resulting from sudden changes in the hormonal status, up to tenfold increase in the androgens, which lead to increased deposition of muscle. Brooks and Fahey (1984) have also made the important observation that the extent of the development and performance of muscle is dependent on the relative maturation of the nervous system. High levels of strength, power, and skill are impossible if the child has not reached neural maturity. Since myelination of nerves is incomplete until sexual maturity, the neural control of muscle function will be limited. Figure 6 illustrates changes in leg strength in a group of boys from the Medford Growth Study followed longitudinally for a period of 12 years, from the age of eight years to 18 years. There is a noticeable increase in the rate of strength gain at about the age of 12 years, which is coincident with the onset of puberty. Similar longitudinal data for girls is not available. From cross-sectional data, however, girls experience a more gradual increase in strength, and do not exhibit a marked change in the rate of strength gain with puberty.
Figure 5 : Gains in leg strength with age in young boys followed longitudinally over a 12-year period. Data from the Medford Growth Study (from Clarke, H. H).
Figure 6 : Changes in means of performance scores of boys and girls from ages 6 to 17 years (data from the President's Council on Physical Fitness and Sports).
Basal Metabolic Rate (BMR)
The BMR, or lowest metabolic rate that the individual attains during a 24-hour day, decreases at a rate of approximately three percent per decade from the age of three through 80. Longitudinal studies that have followed the same individuals over 20-year periods, or longer, suggest a more conservative decrease of only one to two percent per decade. Up to the age of 20 to 30 years, this decrease is assumed to reflect a more efficient metabolism. Beyond 30 years of age, this decrease could be a result of the decrease in lean body weight. It would be interesting to determine if physically active individuals, particularly those performing heavy-resistance exercises on a regular basis, have this same decrease in BMR. Likewise, it would be interesting to determine whether increasing muscle mass through heavy-resistance weight training would increase the BMR in older people. An increased BMR might reduce the degree of fat accumulation that seems to accompany the aging process.
Pulmonary Function A number of cross-sectional studies have demonstrated that lung function is markedly altered by age. During the period of growth, the static lung volumes, as well as the volumes determined during functional pulmonary tests, increase to the time of physical maturity. Shortly after reaching this peak, however, there is a gradual reduction with age. Vital capacity, FEVi.o (the greatest volume of air that can be exhaled in the first second of a forced vital capacity test), residual volume, and forced expiratory flow rate, all exhibit a linear increase with age, up to the age of 20 to 30 years. These changes
are associated with the growth in size of the pulmonary system, which parallels the growth patterns of the child.
The changes in these volumes and flow rates are matched by the changes in maximal ventilatory capacity during exhaustive exercise. Maximal expiratory ventilation (ft max) will increase with age to the point of physical maturity, and then it will decrease with the aging process. From cross-sectional data for males, the VE max, for four- to six-year-old boys, will average about 40 liters per min, increase to from 110 to 140 liters per min at full maturity, and decrease from 60 to 80 liters per min for 60- to 70-year-olds. Females follow the same general pattern, although their absolute values will be considerably lower for each age level, due, primarily, to their smaller stature.
Cardiovascular Function A number of changes occur in cardiovascular function as the child ages. There is a linear decrease in maximal heart rate with age. Young children, under ten years of age, frequently exceed 210 beats per min, while the average 20-year-old has a maximal heart rate of approximately 195 beats per min. It has been estimated that the maximal heart rate decreases by slightly less than one beat per year as the individual ages. The submaximal heart rate response to the same absolute rate of work on a cycle ergometer is higher in the child compared to the adult. This higher submaximal heart rate is a partial compensation for a lower stroke volume which results from a smaller heart size and smaller total blood volume. As the child ages, heart size and blood volume will increase parallel with increases in body size, and stroke volume will thereby increase for the same absolute rate
of work. The higher submaximal heart rate does not totally compensate for the lower stroke volume in the child, thus the cardiac output will be somewhat lower in the child compared to the adult for the same absolute rate of work. The child, to maintain adequate oxygen uptake for these submaximal levels of work, further compensates by increasing the arterio-mixed venous oxygen difference. These submaximal relationships are illustrated in Figure 7. Blood pressure at rest and during submaximal levels of exercise is lower in the child compared to the adult, but will progressively increase to reach adult values during late pubescence.
Figure 7 : Submaximal heart rate, stroke volume, cardiac output and arterio-venous oxygen difference in boy and men at fixed rates of oxygen uptake.
Blood flow to active muscle may be increased during exercise in the child as compared to the adult, due to a reduced peripheral resistance.
During maximal levels of exercise, the smaller heart of the child limits the maximal stroke volume that can be achieved. While the child has a higher maximal heart rate, this higher rate is unable to fully compensate for the lower maximal stroke volume, thus maximal cardiac output is lower in the child. This will be a limitation in the performance of high absolute rates of work, such as a fixed rate of work on a cycle ergometer, since the capacity for oxygen delivery will be less. However, for high relative rates of work, where the child is only responsible for moving his or her body mass, this will not be as serious a limitation.
Maximal Aerobic Capacity The purpose of the basic pulmonary and cardiovascular adaptations that are made in response to varying levels of exercise, or rates of work, is to accommodate the need of the exercising muscles for oxygen. Thus, the increases in pulmonary and cardiovascular function with growth suggest that aerobic capacity, or VO2 max, experiences a similar increase with age. Robinson, in 1938, demonstrated this phenomenon in a cross-sectional sample of boys and men ranging in age from 6 to 91 years. He found that V02 max attained its peak value at 17 to 20 years of age and then decreased as a linear function of age. Others have subsequently reported results that confirm these original observations. Studies of girls and women have shown essentially the same trend, although the female
starts her decline at a much younger age, probably due to an earlier assumption of a sedentary lifestyle. The changes in V02 max with age, expressed in liters-min-', are illustrated in Figure 8.
Figure 8 : Changes in maximal oxygen uptake with age with values expressed in liters rnin-'. When V02 max values are expressed relative to body weight, a considerably different picture emerges (see Figure 9). Values appear to change very little in boys from the age of six years to young adulthood. For girls, however, there appears to be little or no change from six years to 13 years, but from 13 years to young adulthood there is a gradual decrease in aerobic capacity.
Figure 9 : Changes in maximal oxygen uptake with age with values expressed relative to body weight (ml - kg -' - min 1)
How do these changes in aerobic capacity with growth affect the child's performance? For any activity that requires a fixed rate of work, for example, cycling on an ergometer, the low V02 max expressed in absolute liters-min-' will present limitations to endurance performance. However, for activities where the body weight is the major resistance to movement, as in distance running, the child should not be at a disadvantage, since his or her V02 max, expressed relative to body weight, is already at or near adult values. Does this mean that a child should be able to run as fast as an adult? The answer to this question is "no," due to basic differences in mechanical efficiency between the child and the adult. For the same speed on a treadmill, the child will have substantially higher submaximal oxygen consumption. If the child's lactate threshold occurred at the same relative oxygen consumption as an adult (the same percentage of their respective ~702 max), the child would be running at a much slower pace.
Anaerobic Capacity The child has limited ability to perform anaerobic types of activities. This is demonstrated in several ways. First, the child is not able to achieve adult concentrations of lactate in either muscle or blood for submaximal, maximal, and supramaximal rates of exercise. It has been suggested that this reflects a low concentration of the key, rate limiting enzyme of glycolysis, phosphofructokinase. This is also apparent in the inability of the child to achieve high respiratory exchange ratios during maximal or exhaustive exercise-the maximal values are seldom above 1.10, and are frequently below 1.00. Lactate threshold, however, when expressed as a percentage Of V02 max, does not
appear to be a limiting factor in the child, as his or her values are similar, if not somewhat higher, than those of similarly trained adults.
Anaerobic mean and peak power output, as determined on the Wingate anaerobic test is also lower in the child as compared to the adult. Figure 10 illustrates this fact on 306 males who performed the Wingate test with both arms and legs. Mean power output was the average power output for the entire 30-second test. Peak power output was the highest power output attained during any one five-second interval during the 30-second test. Anaerobic power does increase with growth and development, even when the values are expressed relative to body weight, as watts-kg-'.
Figure 10 : Mean (MP) and peak (PP) anaerobic power changes with age, expressed in absolute terms (watts) and relative to body weight (watts-kg-').
CHAPTER 2 ENERGY SYSTEM OF YOUNG ATHLETES
Aerobic PowerAerobic power increases with age during childhood in both sexes and is quite
similar. Girls hardly differ from boys in the prepubertal period but, from the age of 14 years on their aerobic power are significantly lower by about 15%. The maximal aerobic performance capacity in girls reaches a plateau from 14 years onwards while in boys it increases up to the age of 18 years. Thus, even though the aerobic capacity is fully developed aerobic performance continues to improve. That is because other growth factors, such as larger levers, greater musculature, etc. are still developing and govern the effectiveness and mechanical efficiency of aerobic activities. The potential effect of endurance training programs on VO2max is not consistently shown in studies involving children. Endurance training has been shown not to effect aerobic capacity before 11 years. After the age of 12, an improvement in VO2max has been shown in males, particularly swimmers. This suggests that there is an increased trainability of the heart and circulatory system around puberty in males. However, studies at the International Center for Aquatic Research in Colorado Springs have shown that swimmers' aerobic capacity reaches its ceiling level at the time of onset of the adolescent growth spurt. It takes a lot of intense aerobic training to produce shifts in aerobic factors in children. The apparently high threshold of a stimulus for training effects on VO2max in children is
probably related to their naturally active lives. The stresses induced by short-term training are probably small when placed in the context of the overall activities of children. VO2max improvements are similar to those reported for adults when the training volumes and intensities are very high. VO2max training effects are larger in swimmers probably because it is an unnatural and specific activity (the starting point is much lower than those of other everyday activities). Short-term training programs (such as in schools) probably should not even consider improving endurance in pre-pubertal children. Boys and girls 7.6 to 10.3 years have shown a significant improvement in running performance (up to 18%) but without an obvious increase in VO2max. The improvements are probably due to motor coordination and running technique. This suggests that if VO2max is the only criterion for aerobic fitness it may be misleading. Implication : In pre-pubertal children, the gains from endurance training will
largely result from improvements in mechanical efficiency NOT a large change in physical aerobic power. Thus, for endurance improvements, an emphasis on the techniques of performance is more beneficial than the programming of assumed physiological stimulations of training. There is no difference between children and non-trained adults relative to physical capacity at the anaerobic threshold. In children, cardiovascular adaptation is efficient and similar to adults; muscle structure is identical to adults; and glycogen storage mechanics and values are similar to adults.
Anaerobic CapacityUnlike aerobic capacity, the anaerobic capacity of children expressed per Kg of
body weight is much smaller than adults. It is lowest in children and increases progressively with age in both boys and girls. Little to nothing is known about the trainability of anaerobic capacity in children. The ratio of aerobic : anaerobic metabolism contribution to exercise differs between children and adults. "Most researchers agree that a paced 3000-metre run . . . . is less strenuous for children than a vigorous 200-800-metre run . . . . instructions on running speed must be given, otherwise both a 3000-meter run and a 200-800-metre run may be equally strenuous since lactate accumulation depends, among other things, upon running intensity. Even longer distance runs (e.g., 30-min duration) for children are more justified than vigorous short sprints as they may also lead to the maintenance of optimal body composition . . . . it is not the duration but the intensity of the effort which could prove harmful." (Borms, J. 1986.) Implication : Children are endurance animals and are best suited to adapt to
aerobic exercises. Frequent and stressful stimulation of anaerobic metabolism will be particularly fatiguing and if overdone, could be harmful. Children will fatigue rapidly in anaerobic work when compared to their response to endurance work. The major content
of swimming program for children should be "distance" work at a comfortable level (anaerobic threshold and lower) with an obvious concentration on skill, smoothness, and mechanical efficiency.
Strength"In the prepubescent age, muscle weight is about 27% of the total body weight
and the effect of training on muscle hypertrophy is small so that strength gains are perhaps more the result of an improvement in coordination . . . . After sexual maturation [the onset of the adolescent growth spurt], muscular development is influenced by androgenic hormones and the percentage of muscle weight then increases to over 40%." (Borms, J. 1986) Since the increase in testosterone production in adolescent children is markedly higher in boys than girls, boys will become stronger faster and to a higher degree. Implication : If strength training is to be done with pre-pubescent children,
exercises should involve submaximal resistance, such as one's own body weight, light dumbbells, or medicine balls. Sophisticated and restrictive weight exercises, particular on machines, are useless for strength-limited children. General, whole-body activities are more important and beneficial than the same exercises used for post-pubescent athletes.
Speed" . . . a yearly increase in sprint velocity has been noted from age 5 years until
age 16 years for boys, and until age 13 to 15 years for girls. The rate of development of speed seems to accelerate in two phases. A first phase occurs around 8 years of age, both in boys and girls . . . Probable reasons for this are the development of the nervous system and improved coordination of arm and leg muscles. A great variety of exercises involving the whole body should be offered to children to stimulate improvement of this ability. A second phase . . . occurs around 12 years of age for girls and between 12 and 15 years for boys . . . related to the increase in body size with age and the concomitant increase in muscular strength, power, and endurance . . . slightly higher performance levels for boys than for girls until the onset of adolescence when the differences favoring the boys becomes more marked." (Borms, J. 1986)
FlexibilityThere is a gradual increase in flexibility with age as measured on the sit-and-reach
test. However, generalization is not clear because of the absence of studies and data that take into account growth spurts and anthropometrical size changes (e.g., longer arms produce a better sit-and-reach measure).
Coordination and Skill Learning
Most authors agree that the sensitive skill learning period is between 9 and 12 years. Very early training may produce learning of a less economical nature. Later starters would soon catch up. One must not confuse performance with skill. Early maturers will compensate, usually advantageously, for lack of skill with strength and leverage.
: Up to the age of 8, children should enjoy a variety of stimulating
activities to develop a general base of physical and movement aptitudes. From then on, more detailed instruction in particular skills can be entertained but against a background of general stimulation. It has been shown that, in general, children who specialize early will lack the "background" development of capacities for flexible maximum responses in the later years, and higher performance categories, of participation.
Early Maturation" . . . early maturation in boys is an advantage in some sports, but the opposite
applies in girls . . . there is an apparent delay in maturity in sports where females who maintain preadolescent physique seem to have an advantage. An ordering of sports on a continuum from participants demonstrating early maturation through to late maturation might be as follows: alpine skiing, field events, swimming, synchronized swimming, track events, diving, figure skating, gymnastics . . . " (Borms, J. 1986)
Successful female athletes display physical characteristics that favor good performances (more mesomorph, less ectomorph); successful young female athletes have similar somatotypes to older successful athletes.
" . . . There is a trend towards increase linearity in these athletes and this linear physique characterizes the physical attributes of late maturing girls." (Carter, J. E. 1981). Early maturing girls undergo a socialization process which does not motivate them any more to excel in physical exercise. On the other hand, late-maturing girls tend to be socialized into sports participation. Late-maturing girls are older chronologically when they attain menarche and have not yet experienced the social pressures regarding competitive athletics for girls and/or are more able to cope with the social pressures.
Children and AdultsThe child differs in some aspects from the adult and is comparable in others. The
training principles appropriate for both groups are generally different. That is because not only are developmental factors different, but so are the skill/experiences that are taken into each participation realm. Intensive training to acquire specialized sports skills at too early an age has more disadvantages than advantages. Early specialization is by definition achieved at the expense of developing a broader base of fundamental movement skills
such as balance, agility, and coordination, and usually occurs at the expense of learning other sports. Early specialization, in a sense, produces the physical equivalent of a specialist who has little competency outside of the specialty.
TRAINING THE YOUNG ATHLETE
Must special consideration be given to the young athlete when developing individualized programs of training? Generally, the youngster will adapt well to the same type of training routine used to train the mature athlete. This section will look at the specific areas of strength, aerobic and anaerobic training, addressing those issues that are of concern to this age group.
Strength One area of major controversy with regard to muscle development in youngsters is the use of weight training to increase muscular strength and endurance. For many years, young boys and girls were discouraged from using weights for fear that they might injure themselves and prematurely stop their growth processes. Studies on animals suggest that heavy-resistance exercise would lead to a stronger, broader, and more compact bone. However, since it is nearly impossible to load these animals to the same extent as youngsters, it has not been practical to design an experiment that accurately
defines the risks associated with heavy resistance exercise in youngsters. It would appear that the potential for injury and structural damage from heavy-resistance exercise is extremely low, but since the future of the youngster is at stake, it is appropriate to take a conservative approach until additional studies can be conducted. Thus, a program using low weights and high repetitions would be preferred to one using high weights and low repetitions. One of the safest techniques for strength training in youngsters would be to use the isokinetic concept, in which resistance is matched to the force applied, so that the youngster does not have to contend with actual weights, such as a barbells and dumbbells.
It has been suggested that since young, prepubescent boys have relatively low circulating androgen levels, there is no reason to expect them to be able to benefit from strength training at this early age. Several recent studies have demonstrated that prepubescent boys can not only participate in this form of activity safely, but they can also gain substantial increases in strength. In a study conducted by Sewall and Micheli (1986), prepubescent boys and girls took part in a nine-week progressive, resistance-strength training program, 25 to 30 minutes per day, three days a week. They experienced a mean strength increase of 42.9 percent compared to a 9.5 percent increase in a nontraining control group. Weltman and his colleagues (1986) followed 26 prepubertal males with a mean age of 8.2 years through a 14-week strength training program using isokinetic techniques with hydraulic resistance. Isokinetic strength increased between 18 and 37 percent in these young boys. Only one injury was reported which the authors felt was related to the strength training routine. As a result, the boy missed three training sessions.
An additional six subjects reported injuries resulting -from activities of daily living, independent of the strength training program. No boy demonstrated any evidence of damage to epiphyses, bone, or muscle as a result of strength training.
Aerobic and Anaerobic Training Do prepubescent boys and girls benefit from aerobic training (training to improve the cardiorespiratory systems)? This has also been a highly controversial area as several early studies indicated that training prepubescent children did not affect changes in V02 max. Interestingly, even without significant increases in V02 max, these children had substantial improvements in performance, for example, reduced time for running a fixed distance. From the research studies that have been conducted to date, it seems appropriate to conclude that there will be only small increases in aerobic capacity with training in youngsters ten years of age and younger, even though their performances in aerobic activities are improved. More substantial changes in'~02 max appear to occur once the child has reached puberty. The reasons for these findings are not well-defined at this time. Since stroke volume appears to be the major limitation to aerobic performance in this age group, it is quite possible that further increases in aerobic capacity are dependent on growth of the heart. Anaerobic training does appear to improve the anaerobic capacity of children. Following training, children have increased resting levels of creatine phosphate, ATP, and glycogen, and they have an increased activity of
phosphofructokinase, and increased maximal lactate levels in the blood.
Is formal, organized competition or participation in vigorous physical activity damaging to the emotional health and psychological development of the athlete? For the mature athlete, this presents no major problem, but many parents, educators, physicians, and psychologists have expressed concern over the potential for undesirable emotional experiences in the developing young athlete. The question has been raised whether children who compete in formal, highly-organized activities are likely to develop undesirable behavior patterns or psychological damage as a result of the pressures to win and be successful by adult standards. Does the 11 year-old boys competing on the all-star Little League team experience pressures and situations that could lead to immediate or future behavior or emotional problems?
Only limited research has been conducted in this area. Skubic (1954, 1955) studied both Little League and Middle League (13 to 15 years of age) baseball athletes in a small community in California. Using parents' opinions and the Galvanic skin-resistance measurement, she found essentially no difference between the athletes in formal competition compared to those who participated informally in physical education softball. There were few athletes who had any serious emotional problems that could be related to the stress of competition. Generally, her results suggested that formal competition at this age level was not detrimental to the child, but actually facilitated social and emotional growth.
On the other hand, Sherif, et al. (1961) conducted a fascinating study, which has been referred to as the "Lord of the Flies" or "Robber's Cave" experiment. In this study, a group of boys at summer camp were divided into two subgroups. During the initial part of the study, the groups were separated during much of the day, but they had periods of interaction. No problems between the groups developed during this part of the study. For the second phase of the study, the groups were put into situations where they were always in competition with each other in camp life, as well as in sports and games, both for recognition and for tangible rewards. During this phase, members of the individual groups developed strong allegiances to their own group and extreme hostility toward the other group. Night raids, cheating, and other forms of aggressive behavior began to develop. This phase of the study was discontinued when several members of both groups started developing serious psychological disturbances. During the third, and last, phase of the experiment, an attempt was made to bring the two groups back together in cooperative ventures, removing all forms of competition between the groups. It took considerable time to achieve the goal of working in a genuinely cooperative effort.
From these examples, it can only be concluded that competition can have both positive and negative influences on the emotional development of the youngsters. Of major importance is the climate in which the competition takes place. If the climate is such that winning is the only goal and parents are allowed to say and do whatever they please without giving the child sound guidance in coping with the stress of the situation, the child will be likely to have a negative experience. In short, the nature of the child's experience will depend almost entirely on the local situation. If competition is organized
with this in mind, and the goal is to satisfy the needs of the child and not the adult, the experience should be positive and facilitate sound emotional growth and psychological development.
ENERGY CAPACITIES ONLY WEAKLY RELATED IN CHILDREN AND ADOLESCENTS
Only a weak relationship was found between the aerobic and anaerobic capacities in children and adolescents classified according to maturational age.
: The type of physical performance capacity exhibited by pre-pubertal
children is not a sound index for predicting post-pubertal athletic capabilities. One cannot, with any moderate degree of confidence, conclude that a successful pre-pubertal sprinter will be just as successful in sprinting during adolescence. Performance capacities are weak predictors of later performances and therefore, are not sound bases for talent identification.
PRE-PUBERTAL CHILDREN HAVE ONE ENERGY SYSTEM?
In both male and female children, those who performed best anaerobically also performed best aerobically. In children, energy systems appear to be able to compensate for each other and "cross" the line of supposed specialization. There is no evidence of metabolic specialization in pre-pubertal children.
Implication : When planning training and fitness programs for pre-pubertal children, there is no point in differentiating between anaerobic and aerobic work. General fitness will be accommodated within the capabilities of children of this age.
TESTING PHYSICAL FITNESS IN CHILDREN
Field tests to measure the capability of children to do certain classifications of physical work are just as valid as are laboratory assessments. The 50 yd run is a good measure of anaerobic capability and the 1600 yd run valuable for aerobic assessment. Implication : The fitness of pre-pubertal children is measured satisfactorily by
convenient simple running tests.
How Much Weight-Training For Children?
It was found that weight training two times per week was equally effective for developing strength as was three times. Implication : In growing children and youths, there is no need to do a "lot" of
weight-training. Two times per week appears to be quite sufficient to develop significant changes. More frequent sessions do not produce any more development.
STRENGTH TRAINING RESPONSE OF CHILDREN
The effects of eight weeks of strength training followed by eight weeks of detraining in children (7-12 yr) were evaluated. Sessions were conducted twice per week. A group matched for age and maturity level served as a control group. The trained group improved leg extensions (53.5%) and chest press (41.1%). Controls improved 7.9%. Vertical jump and sit-and-reach flexibility did not change in any significant manner. During detraining, losses in strength were evident after four weeks, with the legs losing more strength than the upper body. Implication : Twice-per-week strength training is sufficient to dramatically
improve the strength of children over gains that would be expected by maturation. Detraining occurs with inactivity as with any trained effect. Weight-bearing muscle groups (legs) were seen to detrain more than the upper body.
Strength Training Effects Different For Prepubescent Males And Females
The effect of an isoinertial (isotonic) strength training program on isometric strength in prepubescent females was investigated. An experimental and control group
were used. The training response was different to that of previously published work with prepubescent males. Throughout the change and detraining phases of the study, there was no change in isometric measures or positions. Implication : The specificity of strength training may operate differently in
prepubescent females than in males.
Strength Training In Children
Early studies and theorists have generally supported the view that resistance (strength) training in prepubescent children is ineffective. This study performed a metaanalysis on published studies that used Ss with a maximum age of 12 years for girls and 13 years for boys. From 25 studies which showed an increase in strength in children, 9 were sufficiently detailed and controlled to assess common magnitudes of effect. Generally, improvements of between 13 and 30% were obtained. The size of the effect was modified by the various variables associated with resistance training (loads, frequency, type of exercise, sessions per week, etc.). Three studies were found that demonstrated no change. The authors advise that since studies which show changes are published with a much higher frequency than those
which yield no differences, the overall meta-analysis could be biased (Falk, B., & Tenenbaum, G. 1996). Generally, adults and adolescents demonstrate greater absolute increases in strength but prepubescents demonstrate an equal or greater relative percentage gain. No differences in gains were found between genders in children. As with almost all strength programs rates of gain are highest at the start and largely due to learning to do the skills involved in a more economical manner. Studies in this area have not been designed particularly well. Many factors need to be controlled. Simply giving a weight program and measuring changes does not shed light on effects because of the many confounding variables associated with this activity.
Strength training programs are effective with prepupbescent
children. The dynamics and limits of this form of training have not been determined for this population. Coaches are advised to be cautious when employing this training activity.
CHAPTER 8 AEROBIC TRAINING IS LIMITED IN CHILDREN
Cardio-respiratory function develops throughout childhood. Lung volume and peak- flow rates steadily increase until full growth. For example, maximum ventilation increases from 40 L/min at five years to more than 110 L/min as an adult (Wilmore & Costill, 1994). This means that children have higher respiratory rates than adults, 60 breaths/min compared to 40 breaths/min for the equivalent level of exercise (Sharp, 1995). The ventilatory equivalent for oxygen is also higher in children, VE/V02 = 40 for an eight-year-old compared to 28 for an 18 year-old. This means that children have inferior pulmonary functions to adults. Cardiovascular function is also different for children. They have a smaller heart chamber and lower volume than adults. This results in a lower stroke volume than adults, both at rest and during exercise. Chamber size and blood volume gradually increase to adult values with growth. Children compensate for the smaller stroke volume by having higher maximal heart rates than adults have. For a mid-teenager, max heart rate could be more than 215 beats/min compared to a 20 year-old whose max heart rate will be around 195200 bpm (Sharp, 1995).
However, the higher heart rates cannot fully compensate for the lower stroke volume and so children's cardiac output, measured in L/min, is lower than adults (Wilmore & Costill 1994). Children can compensate a little again, as their arterial venous oxygen difference 43
is greater. This suggests that a greater percentage of the cardiac output goes to the working muscles than in adults (Wilmore & Costill, 1994). An in-school 12-week aerobic training program was designed for girls (N = 24) and boys (N = 13). Three 30 min training sessions were offered per week. It was found that training changes occurred but were of less magnitude than would be expected of adults. This finding supports the general literature contention that children are more limited in aerobic training adaptations than adults. Implication : Prepubescent children should be trained aerobically but
expectations for improvement should be less than that afforded adults.
Chidren Have Only General Metabolic Responces
The objective information in female youth energy responses in sprint activities is quite scant. However, it appears that children who specialize in sports do not exhibit a specialized metabolic response. They appear to be "metabolic non-specialists." Children do not seem to display the wide variations in metabolic response capabilities seen among adults, nor do they appear to have high levels of response in any one metabolic system. Implication : It may be a false premise to concentrate on developing specific
energy systems in children as young as 12 years of age. Rather, what exercises they do
should be energized by training responses to a variety of stimuli which, if applied to adults, would not produce specialized metabolic responses.
Training Effects In Young Boys (11-13 Yr)
Boys (11-13 yr, N = 18) from different sports (4 endurance runners, 7 tennis players, 4 weightlifters, 3 sprinters) were divided into two groups according to a "fast" group (M = 59% Type II fibers) and a "slow" group (M = 60.6% Type I fibers). A variety of tests were performed. Fibers were divided into (a) Type I slow-twitch oxidative, (b) Type IIA fast-twitch oxidative, and (c) Type IIB fast-twitch glycolytic. The fiber distributions were as follows:
Category Type I Type II Type IIA Type IIB
Fast Group 40.8% 59.2% 36.5% (61.6%) 22.7% (38.4%)
Slow Group 60.4% 39.4% 22.8% (57.9%) 16.6% (42.1)%
Source : Mero, A., Jaakkola, L., & Komi, P. V. (1991). Relationships between muscle fibre characteristics and physical performance capacity in trained athletic boys. Journal of Sports Sciences, 9, 161-171.
Few significant differences were revealed. Reaction time to sound and choice reaction time were faster for the fast group and it also had a greater rate of force development. A weak significant relationship between Type II fiber area and blood lactate levels ( r = .53) was revealed. There were no differences between running velocity, maximal oxygen uptake, or anaerobic characteristics. The similarity in aerobic capacity stemmed from the training program of the boys (general endurance within each sport). The Type IIA fibers made up the inherent difference by adapting to oxidative work. It was shown that even though the "fast" boys inherited 66.5% more Type II fibers, a greater percentage of them switched to oxidative functioning so that between the groups the fast group had 77.3% and the slow group 83.2% of fibers functioning oxidatively. This suggests that in young boys, the adaptability of fibers allows individuals to perform a variety of tasks, particularly of an endurance nature. Implication : In young boys, the adaptability of the inherited fiber distributions
to different types of training makes measures of aerobic or anaerobic capacity relatively useless as a performance predictor. However, reaction time and power development rates may discriminate between fast- and slow-twitch dominant pubescent boys. This is about all that can be used to identify capacity talent that will not be revealed in a current sporting performance.
Early Learning / Training Is Not Necessarily The Best
Certain periods in the life of young children are marked by times of particular sensitivity. For example, in McGraw's (1935) attempts to modify the behaviors of identical twins by teaching them a number of physical activities, some credence to the "appropriate times for learning" postulation was presented.
The onset of walking was not affected by preemptory practice or help. It is a phylogenetic behavior that is largely "programmed" into the natural development timing of the youngster. It cannot be "speeded-up."
Roller skating, an unnatural activity but closely allied to walking, developed almost in concert with walking itself.
A number of other activities were actually made worse by early practice because of bad skill habits developed or the negative occurrences associated with the learning experience.
Starting a sporting experience at a very young age is not
necessarily advantageous. It would seem that if one was to design development in a sport, the following are appropriate:
Provide a wide variety of activities so that generalized basic gross skills are developed.
Pay little attention to skill intricacies, instead being satisfied with gross motor movement patterns.
Provide much activity that leads to successful outcomes. Avoid at all costs, the implementation of adult rules and sport dynamics, instead providing activities appropriate for the social, intellectual, and development stages of the participants.
There are critical periods for learning that vary from sport to sport. For each kind of coordinated muscular activity there is an optimum for rapid and skillful learning.
CARDIOVASCULAR RESPONSES IN CHILDREN AND ADULTS
Submaximal cardiovascular responses at a given rate of work on a treadmill and cycle ergometer were compared between children (M = 12; F = 12) and adults (M = 12; F = 12). Cardiac output was significantly lower, but heart rate, total peripheral resistance, and stroke volume were significantly higher, in children of both sexes than comparable adults in both forms of exercise. The smaller amount of muscle mass in children would be stressed to a relatively greater extent than in adults. Greater metabolic by-products and heat would be produced per unit of muscle which would: a) increase the amount of oxygen liberated from hemoglobin in the muscle, and b) increase vasodilation of the arteries entering the muscles. Both these effects contribute to a higher a-vO2 difference in children in exercise (Turley, K. R., & Wilmore, J. H. 1996).
Submaximal cardiovascular responses are different between
children and adults. These differences are related to smaller hearts and less total muscle volume in children. These differences are observable irrespective of the form of exercise.
CHAPTER 10 SPRINT AND ENDURANCE TRAINING IN CHILDREN
Groups (sprint, endurance, and control) of children were trained for 20 minutes in a specific program four times a week for six weeks. The science of developmental physiology can supply answers to certain important questions regarding the training of children. One such question is: should children perform adult-type endurance training in reduced quantities, or should they be performing a different type of training that is tailored to their physiology? Science suggests the latter is true and that the type and intensity of training that is most effective for developing endurance in the young will be different from that used by adults. The average adult model for endurance training involves an intensity of 75% of max heart rate maintained for 20 to 30 minutes. If this is performed 3 to 5 times a week, then the average adult can expect a 25% improvement in VO2max. Both an increase in stroke volume and an improvement in O2 respiration and metabolism in the working
muscles due to increased capillaries, mitochondria and enzyme activity cause this improvement in fitness. Several training studies have been carried out on children to find out what effect a cardiovascular (CV) training programme will have on fitness levels. In general, the research shows that if children follow a 3 to 5 times a week routine of at least 20 minutes continuous activity for 12 weeks, then improvements in VO2max of 7 to 26% is possible. On average, though, and the results of some of the better-controlled experiments support this, a child can expect a 10% improvement in VO2max after following an 'adult-like' CV training programme. The consensus from the research is that children can improve their aerobic fitness but not to the same degree as adults, when following a similar training programme.
No differences were observed between the two training groups in either aerobic or anaerobic performance parameters. Differences were observed between the training a control groups. The training effects of each different program were not specific indicating that children can be trained aerobically in a sprint (anaerobic) program. (Dykstra, G. L., Demetriou, D. G., Copay, A. G., & Boileau, R. A. 1996). Implication : The effects of specific training programs are general in children.
Any form of training trains all capacities in growing children.
10.1 Work Capasities In Children
Children typically demonstrate a higher ventilatory threshold (VAT), expressed as %VO2max, than adults. This investigation found that the greater children's (M = 11; F = 10) values are best explained by lower levels of relative anaerobic capacity rather than superior aerobic power ( Rowland, T., & Boyajian, A,1994) Implication : The type of work at children's practices should be appropriately
programmed. A greater percentage of aerobic work, when compared to that which better matches adults' capabilities, should be included.
VO2max AND GROWTH
Research has consistently shown that relative VO2max (maximal aerobic power) declines from the onset of adolescence. However, the use of mean VO2maxand mean age may be misleading. The relationship is reported assuming that duration and distance in the testing protocol are unimportant. The highest mean speed for a protocol is used to determine VO2max at the point of perceived exhaustion ( Orban, W. A., & Kozak, J. F. 1997). Males (N = 84) were studied for 10 years from the age of 7 through 16. It was found that relating VO2maxto the specific variables of duration and distance a well as speed affects the relationship between VO2max and age. A different understanding between age and VO2max resulted. 1. VO2max, relative to performance, accelerates, rather than declines, through adolescence.
2. To validly comprehend VO2max, it must be related to a specific maximal performance of a given distance or duration under specific performance conditions. Implication : The traditional use of VO2max produces a spurious understanding
for actual performance. Adolescents increase in aerobic performance for specific tasks as age increases. Thus, it becomes important to talk of maximal aerobic power for what task rather than just quoting a number as if there is a very simple entity of VO2max that exists independent of task quality. Performance features must be included in any consideration of aerobic capacity.
Growth, Puberty And Exercise
Puberty is characterized by the onset and continued development of secondary sexual characteristics and an abrupt onset of linear growth. The secondary sexual characteristics are a result of androgen production from the adrenals in both sexes (adrenarche) and testosterone from the testes in the male and estrogens from the ovaries in females (gonadarche). During early childhood linear growth velocity declines rapidly to reach a constant childhood rate of approximately 5.5 cm per year. With the onset and progression of pubertal development, the rate accelerates markedly to reach a peak during midadolescence (later in the developmental process in boys compared with girls) and then diminishes toward zero as the bony epiphyses fuse. Pubertal growth spurt cannot occur
without sufficient quantities of growth hormone. hGH alone apparently is not sufficient, since important physiological synergism exists between the gonadal axis and hGH secretion coincident with the progression of puberty. Shortly after cessation of linear growth, the circulating pattern of hGH returns to the prepubertal configuration with the result that the hGH concentration versus time profiles in young men are remarkably similar to those in prepubertal boys, but greater than those in older men despite a continued rise in serum testosterone concentration. hGH secretion (and other pituitary hormones) occurs in a repetitive, burst-like manner (Rogol, A. D. 1994). The pubertal growth spurt is likely subserved by altered neurosecretory dynamics for growth hormone. The augmented hGH secretion apparently results from an increase in the maximum rate of hGH release rather than from an increase in hGH burst frequency caused in the main by increasing amounts of circulating gonadal steroid hormones. The markedly altered hormone levels subserve the equally profound changes in body composition, regional fat distribution, and muscular strength. Gonadal steroid hormones strongly regulate growth and hGH secretion at puberty. However, any straightforward relationship between growth velocities and the circulating hGH concentrations, or attributes of hGH neurosecretion, is diffused by the added components of hGH binding proteins, circulating IGF-1 and its binding proteins, and the complex metabolic signals that reflect the relative fatness of an individual, even when well within the physiological range.
Exercise And Growth
The "anabolic effects" of exercise are defined as constructive or biosynthetic metabolic processes involved in tissue adaptation to physical activity. A sizable anabolic stimulus arises from the relatively modest physical activity of daily living. Excessive training may have adverse effects (it has been reported that a reduction of growth potential occurs in female gymnasts engaged in intense training). Naturally occurring levels of physical activity, energy expenditure, and muscle strength exhibit some of their most rapid increases during childhood and puberty. Most children pass through activity phases that far exceed those of adults, and some biologically essential, minimal threshold of activity is reached by the vast majority of healthy children. The effects of exercise on somatic growth become important only if a child's level of activity (possibly due to social, psychological, or disease causes) falls below this biological threshold. Exercise modulation of growth does not imply that increasing levels of physical activity will increase somatic growth in healthy children. Increases in heart mass or skeletal muscle mitochondrial density may have little impact on overall body size. Conflicting results have been obtained from studies done to test the effect of training on growth rates in children. It may be useful to focus on exercise anabolic effects in terms of cardio respiratory adaptation rather than somatic growth. There is evidence that an integrated cardio respiratory and muscular response to exercise may be modulated by childhood patterns of
physical activity and exercise. The time to respond to the onset of exercise and to recover is faster in children than in adults. These responses are also faster in lean children than those who are obese. This suggests that CO2 transport from cells to the lungs is delayed by the high solubility of CO2 in adipose tissue. This may also explain the differences in CO2 transport dynamics between adults and children since adiposity increases with age in adults. Children also work less efficiently in terms of oxygen cost of exercise than do adults. Patterns of physical activity during childhood may affect the incidence and morbidity of disease later in life.
Peripheral mechanisms of exercise stimulation. Energy generated by exercise is transformed into signals that stimulate cellular
anabolism at the site of the exercise. Physical stretch profoundly influences endothelial cell orientation and actin cytoskeleton organization. In exercising muscle, PO2 and pH are low and lactate concentrations are high. Similar conditions can be found in the interior milieu of wounds. The healing wound is characterized by new capillary and collagen formation which suggests that there is a parallel between wound healing and exercise-induced anabolism (Cooper, D. M. 1994).
Physical activity is a naturally occurring stimulator of growth hormone (hGH) release into the circulation. hGH induces tissue production of IGF-1 (insulin-like growth factor 1) and elevations in serum IGF-1. An hypothesis exists that exercise induced hGH release is partly responsible--directly or indirectly--for anabolic effects of exercise. hGH plays an important role in anabolic effects of exercise, but the mechanism of regulation is not known. The role of the pattern of physical activity in the adult or developing child may prove to be particularly important. hGH given in pulses results in more and better growth than when it is given continuously. Thus, the body has a mechanism that pulses hGH rather than continuously introducing it into the system. It is intriguing to note that activity patterns in children are characterized by bursts of exercise, perhaps being a pattern that optimizes the anabolic effects of exercise in the growing child. Both hGH -dependent and hGH -independent pathways likely exist and link exercise with tissue anabolism.
Nutritional factors. One possible mechanism that affects exercise-stimulated hGH release is diet.
Glucose ingestion leads to hyperglycemia that inhibits hGH release. Meals high in fat could inhibit pituitary hGH release either by the direct effect of free fatty acids on the pituitary, or might cause release of gastric and pancreatic somatostatin. A single high-fat meal prior to exercise can interfere with performance and prolong the period of recovery.
Structure-function interactions. The athlete's heart is more massive in both absolute and normalized to body
weight terms. The combination of a high-fat diet and inactivity contributes to the development of obesity, hypercholesterolemia, hypertension, and coronary artery disease. One could argue that there is no need in healthy children to attempt to impose patterns of physical activity since the natural inclination of children is to be active (they maximize the anabolic effects of exercise). The use of growth promoting agents may have different long-term physiological consequences in children compared with adults. Drug use touted to boost body height, strength, and athletic prowess in normal children and young adults should be construed as being abuse.
CHAPTER 12 SPORT INJURIES IN CHILDREN
Reasons for Concern Young athletes are not merely small adults. Their bones, muscles, tendons, and
ligaments are still growing, which makes them more susceptible to injury. Growth plates - the areas of developing cartilage where bone growth occurs in youngsters - are weaker than the nearby ligaments and tendons. What is often a bruise or sprain in an adult can be a potentially serious growth plate injury in a young athlete. Young athletes of the same age can differ greatly in size and physical maturity. Some youngsters may be physically less mature than their peers and try to perform at levels for which they are not ready. Parents and athletic coaches should try to group youngsters according to skill level and size, not chronological age, particularly during contact sports. If this is not practical, they should modify the sport to accommodate the needs of children with varying skill levels.
Types of Injuries Injuries among young athletes fall into two basic categories: overuse injuries and
acute injuries. Both types include injuries to the soft tissues (muscles and ligaments) and bones. Acute injuries are caused by a sudden trauma. Common acute injuries among young athletes include contusions (bruises), sprains (a partial or complete tear of a ligament), strains (a partial or complete tear of a muscle or tendon) and fractures. But not all injuries are caused by a single, sudden twist, fall, or collision. A series of small injuries to immature bodies can cause minor fractures, minimal muscle tears, or progressive bone deformities, known as overuse injuries. As an example, "Little League Elbow" is the term used to describe a group of common overuse injuries in young throwers involved in many sports, not just baseball. Other common overuse injuries occur in the heels and knees with tears in the tissue where tendons attach to the leg bone or the heel bone. Contact sports have inherent dangers that put young athletes at special risk for severe injuries. Even with rigorous training and proper safety equipment, youngsters are at risk for severe injuries to the neck, spinal cord, and growth plates. However, following the rules of the game and using proper equipment can decrease these risks.
Soft tissue injuries
Fortunately major sports-related injuries are rare in young people. About 95% of sports injuries are due to minor trauma involving soft tissues-bruises, muscle pulls, sprains (ligaments), strains (muscles and tendons), and cuts or abrasions. Little sports time is lost from these injuries. Moreover, sports injuries occur more frequently in physical education classes and free-play sports than in organized team sports. Minimal safety precautions and supervision can prevent many injuries.
SprainsAlmost one-third of all sports injuries are classified as sprains. A sprain is a
partial or complete tear of a ligament, which is a tough band of fibrous connective tissue that connects the ends of bones and stabilizes the joint. Symptoms include the feeling that a joint is "loose" or unstable; an inability to bear weight because of pain; loss of motion; the sound or feeling of a "pop" or "snap" when the injury occurred, and swelling. Not all sprains produce pain, however.
StrainsA strain is a partial or complete tear of a muscle or tendon. Muscle tissue is made
up of cells that contract and make the body move. A tendon consists of tough connective tissue that attaches muscles to bones.
The most common sports injury contusions (bruises) rarely cause a student athlete to be sidelined. Bruises result when a blunt injury causes underlying bleeding in a muscle or other soft tissues. Prompt treatment for soft tissue injuries usually consists of rest, applying ice, wrapping with elastic bandages (compression), and elevating the injured arm, hand, leg or foot. This usually limits discomfort and reduces healing time. Proper first aid will minimize swelling and help the physician establish an accurate diagnosis.
Spinal cord injuriesAlthough spinal cord injuries in sports are rare, ten percent of all spinal injuries
occur during sports, primarily diving, surfing and football. They can range from a sprain to paralysis in the arms and legs (quadriplegia) to death. Participants in contact sports can minimize the risk of minor neck spinal injuries-sprains and pinched nerves-by doing exercises to strengthen their neck muscles.
Skeletal injuriesA sudden, violent collision with another player, an accident with sports equipment
or a severe fall can cause skeletal injuries in the growing athlete, including fractures. Fractures constitute a low five to six percent of all sports injuries. Most of these breaks occur in the arms and legs. Rarely are the spine and skull fractured.
More common, however, are stress fractures and ligament-bone disruptions that occur because of continuing overuse of a joint. The main symptom of a stress fracture is pain. Frequently, initial x-rays do not show any signs of a stress fracture so the athlete is permitted to return to the same activity. Unfortunately the pain often returns or continues, but the athlete keeps playing. The most frequent places stress fractures occur are the tibia (the larger leg bone below the knee), fibula (the outer and thinner leg bone below the knee), and foot. "Little League elbow" can result when a pitcher's repetitive throwing puts too much pressure on the elbow bone's growth centers. This painful condition results from over usage of muscles and tendons or from an injury to the cartilage surfaces in the elbow. In the growing athlete's musculoskeletal system, pain from repetitive motion may appear somewhere besides the actual site of the injury. For instance, a knee ache in a child or adolescent may actually be pain caused by an injury to the hip.
12.3 Diagnosis and treatmentChildren and teens often experience some discomfort with athletic activity. Their bones and muscles are growing, and their level of physical activity may increase with a sudden, intense interest in sports, so some aches and pains can be expected. Still, their complaints always deserve careful attention. Some injuries, if left untreated, can cause permanent damage and interfere with proper physical growth.
Whether an injury is acute or due to overuse, a child who develops a symptom that persists or that affects his or her athletic performance should be examined by an orthopedic surgeon. A child should never be allowed or expected to "work through the pain." Signs that warrant a visit to an orthopedic surgeon include:
Inability to play following an acute or sudden injury. Decreased ability to play because of chronic or long-term complications following an injury.
Visible deformity of the athlete's arms or legs. Severe pain from acute injuries which prevent the use of an arm or leg.
Prompt treatment can often prevent a minor injury from becoming worse or causing permanent damage. During the evaluation, the orthopedic surgeon will inquire as to how the injury occurred and will examine the child. If necessary, the doctor may perform X-rays or other tests, to evaluate the bones and soft tissues. The basic treatment for many simple injuries is often "R.I.C.E."-Rest Ice Compression Elevation. Treatment for a child with any significant injury will usually involve specific recommendations for temporary or permanent adjustment in athletic activity. Depending on the injury's severity, treatment may range from simple observation with minor changes
in athletic level to a recommendation that the athletic activity be discontinued. Some combination of physical therapy, strengthening exercises, and bracing may also be prescribed. A basic component of any treatment plan is the orthopedic surgeon's ongoing assessment of the child's physical condition until signs of healing and reduction of symptoms occur. Successful treatment requires cooperation and open communication among the patient, parents, coaches, and doctors. Diagnosis of any sports-related orthopedic injury should be made promptly by orthopedic surgeons, physicians who specialize in the care of the musculoskeletal system. The physician usually will ask the young athlete how the injury occurred, then follow with questions about the type of pain-whether it is a stabbing pain, a dull ache or throbbing-the location of the pain, and the sport in which the athlete was involved. During the physical examination, the orthopedist will ask the athlete to move the affected area to determine whether the child's motion has been affected. The orthopedist will gently touch the area to observe for obvious skeletal abnormalities. X-rays or other radiographic tests may be ordered, depending on the athlete's condition and the doctor's need for additional information. Orthopedic surgeons have been in the forefront of treating musculoskeletal system injuries and have a long tradition of caring for young athletes. In the last two decades, they have analyzed and clarified young athletes' psychological needs, conditioning, training, and susceptibility to physical injury. They provide early and comprehensive care
of orthopedic injuries. This can help young athletes heal and return to competition with less chance of repeated injury. Treatment varies according to the patient's condition, but it may include bed rest, elevation, compression bandages, crutches, cast immobilization or physical therapy.
12.4 Female athletesFemale involvement in sports has increased tremendously at the high school level-by 700% over the last 15 years. Although early studies indicated that female athletes needed to train at lower levels of intensity than male athletes, it appears that this was more a social than a physiological problem. Today's female athlete is able to train and frequently compete at levels that rival many of the best male athletes. Although there are differences in performance that are sex-related, athletic injuries are related more to the player's sport than sex.
12.5 Risk and benefitsSports activity by young people is generally safe with low risks and high benefits. The major goal should be enjoyable participation. Exposure to competitive and noncompetitive sports encourages the development of fitness, motor skills, social skills and life-long appreciation for sports.
Orthopedist is a medical doctor with extensive training in the diagnosis, and non-surgical and surgical treatment of the musculoskeletal system, including bones, joints, ligaments, tendons, muscles and nerves.
CHAPTER 13 GUIDELINES FOR PREVENTING SPORTS INJURIESThe American Academy of Orthopedic Surgeons, Pediatric Orthopedic Society of North America, Canadian Orthopedic Association, and American Orthopedic Society for Sports Medicine designed Play It Safe! to help parents, coaches, and children prevent sports injuries. Play It Safe! Encourages children to:
Be in proper physical condition to play a sport. Know and abide by the rules of the sport. Wear appropriate protective gear (for example, shin guards for soccer, a hardshell helmet when facing a baseball pitcher, a helmet and body padding for ice hockey).
Know how to use athletic equipment (for example, correctly adjusting the bindings on snow skis).
Always warm up before playing.
Avoid playing when very tired or in pain.
Play It Safe Young athletes need proper training for sports. They should be encouraged to train for the sport rather than expecting the sport itself to get them into shape. Many injuries can be prevented if youths follow a regular conditioning program with incorporated exercises designed specifically for their chosen sport. A wellstructured, closely supervised weight-training regimen may modestly help youngsters prepare for athletic activities. Young athletes should have their coaches help them design a conditioning program suited to their needs.
Parents should make sure their child's coaches have the appropriate qualifications to supervise a particular sport, provide well-maintained safety equipment, and help with proper conditioning for that sport.
An estimated 500,000 young athletes, boys and girls, use black-market anabolic steroids to improve their athletic performance. Steroids have been shown to increase muscle mass, but they can cause serious and potentially life-threatening complications and should be avoided.
Youth sports should always be fun. The "win at all costs" attitude of many parents, coaches, professional athletes, and peers can lead to injuries. A young athlete striving to meet the unrealistic expectations of others may ignore the warning signs of injury and continue to play with pain.
Coaches and parents can prevent injuries by fostering an atmosphere of healthy competition that emphasizes self-reliance, confidence, cooperation, and a positive self-image, rather than just winning.
Youths, coaches, and parents should Play It Safe! Your orthopedist is a medical doctor with extensive training in the diagnosis and nonsurgical and surgical treatment of the musculoskeletal system, including bones, joints, ligaments, tendons, muscles, and nerves.
EVERCISES FOR YOUNG ATHLETES
Staying injury-free throughout the sports season requires a proper conditioning and exercise program. Here are some stretching exercises developed by the American Academy of Orthopedic Surgeons that young athletes can perform before participating in any athletic activity. Athletes must do each one of the exercises carefully, speed is not important. Once the exercise routine is learned, the entire program should take no longer than 10 minutes. It also is important to warm up before doing any of these exercises. Good examples of warm up activities are slowly running in place and walking for a few minutes.
Seat Straddle LotusSit down; place soles of feet together and drop knees toward floor. Place forearms on inside of knees and push knees to the ground. Lean forward, bringing chin to feet. Hold for five seconds. Repeat three to six times.
Seat Side StraddleSit with legs spread; place both hands on same ankle. Bring chin to knee, keeping the leg straight. Hold for five seconds. Repeat three to six times. Repeat exercise on opposite leg.
Seat StretchSit with legs together, feet flexed, hands on ankles. Bring chin to knees. Hold f