The Young Athlete

The energy and nutrient requirements for growth and development are so high that it is difficult to imagine how growing children who are involved in regular, intense physical activity can possibly meet their nutrition needs unless extraordinary measures are taken.¹⁸ An inadequate energy supply may result in a failure to achieve the genetically prescribed growth potential, and insufficient nutrients may result in poor development of organ systems. For instance, a poor calcium uptake during the adolescent growth spurt will result in less than optimal bone density, which has a lifetime of health implications. Careful attention to the provision of an adequate energy and nutrient intake is the essential construct for ensuring that youth sports result in healthy outcomes. In particular, athletes who achieve elite status at a young age, as is typical of female gymnasts, may fail to obtain sufficient nutriture at a time when growth and sports-related training and performance stresses are at their highest. These athletes should be frequently assessed to ensure they remain in a healthy state and have a normal growth velocity.

The adolescent growth spurt in girls begins around the age of 10 or 11 and reaches its peak by age 12; girls typically stop growing by age 15 or 16. The adolescent growth spurt in boys begins about 2 years later at age 12 or 13 and reaches a peak by age 14; boys typically stop growing by the age of 19. It is common for girls and boys to grow approximately 11.8 inches (30 centimeters) between ages 5 and 10; but boys have a greater than 3.9 inch (10 centimeter) per year growth during the adolescent growth spurt, and adolescent girls have a greater than 3.5 inch (9 centimeter) growth per year during the adolescent growth spurt. It is estimated that 25 percent of the total bone mass is acquired during the adolescent years.¹⁹ Although the stimulation imposed on the skeleton through physical activity is important for bone development, adequate calcium, protein, and energy intakes are also critical during this period. (See table 11.2 for a summary of height and weight values of children and adolescents.)

Adolescence is the time when girls achieve menarche. Less than 10 percent of girls in the United States start to menstruate before 11 years, and 90 percent of all girls in the United States are menstruating by 13.75 years of age, with a median age of 12.43 years.²⁰Athletic females typically begin menstruating 1 to 2 years later.21

The blood loss experienced approximately every 4 weeks by girls who are having menstrual periods is an important nutrition consideration. The iron loss in conjunc-tion with the periodic bleeding may predispose adolescent girls to iron deficiency or iron-deficiency anemia that, if allowed to occur, would have a significant impact on endurance capacity. Although all adolescent girls should be cognizant of the importance of obtaining an adequate iron intake, athletic girls must make a particular effort to obtain enough of this mineral. The DRI for iron is 15 milligrams per day for girls between the ages of 14 and 18. This represents nearly a 100 percent increase over the iron requirement for girls between the ages of 9 and 13, when the DRI for iron is 8 milligrams per day. Obtaining 15 milligrams of iron per day is not easy, even if the athlete is a red-meat eater. For non-meat-eating athletes, regularly obtaining 15 milli grams of iron daily becomes nearly im possible without iron supplementation.²² (See table 11.3 for the iron content of selected foods.) If adequate iron consumption from food is not possible, the risk of iron deficiency, reduced performance, and impaired immune function associated with inadequate iron intake should motivate athletes to seek a well- tolerated strategy for consuming enough iron.²³

Consumption of sufficient energy is critically important for ensuring normal growth and development and supporting physical activity. It appears that substrate distribution is less important for young athletes than it is for adults. The general adult recommendation for the distribution of substrates is 60 percent from carbohydrate, 15 percent from protein, and 25 percent from fat, but the energy utilization pattern of children may allow for a greater proportion of calories from fat. Studies have found that children use more fat and less carbohydrate than adults during endurance activities and more intense activities.^24,25 Because fat is a more concentrated source of energy, a slightly higher fat intake may make it easier to satisfy the high caloric requirements of these young athletes.

Adolescent females, including adolescent female athletes, often diet to control the change in body morphology and weight associated with growth. Dieting may increase the risk of eating disorders, particularly among adolescent female athletes involved in sports where appearance and size matter (e.g., diving and gymnastics). Compared with athletes in team sports, athletes in these sports are at greater risk of having inadequate intakes of energy, protein, and some micronutrients including calcium and iron. These are not minor issues; an inadequate calcium intake could predispose a young athlete to stress fractures and later osteoporosis, and an iron deficiency leads to poor endurance. Studies have confirmed that energy and nutrient intakes of male and female adolescent athletes, despite being better than that of nonathletes, are below recommended levels, which increases disease and injury risk and diminishes athletic performance potential.²⁶

Typical school schedules that mandate a breakfast before school, a moderate lunch at midday, and a dinner that often follows sports practice create an environment that guarantees an energy imbalance. Athletic children should eat at frequent intervals to increase their total energy and nutrient exposure, to guarantee that sufficient energy is provided when it is most needed, and to reduce the chance of energy deficits that can encourage the loss of lean mass and the relative increase in fat mass.

The risk of athletes developing musculoskeletal injuries during periods of fast growth is high. This is not to say that physical activity is bad for children. On the contrary, the right amount and intensity of physical activity stimulates musculo skeletal development. However, excess physical activity that does not allow for sufficient rest and nutrient intake can result in overuse injuries, including tendinitis, Osgood-Schlatter disease, and stress fractures.²⁷ In addition, secondary amenorrhea often occurs during periods of intense physical activity. To avoid overworking specific muscle groups or skeletal areas, it has been suggested that young children should participate in a variety of sports and specialize in a specific sport only after puberty. Those who follow this strategy perform better, have lower injury risk, and continue in the sport longer than those who specialize in a single sport early.²⁸