Physical Growth and Sexual Maturation of Adolescents

A growth spurt in boys occurs sometime between ages of about 12 and 16, with the peak typically between ages 13 and 14; a gain of > 10 cm can be expected in the year of peak velocity. A growth spurt in girls occurs sometime between ages of about 9½ and 13½, with the peak typically between ages 11 and 12½; the gain may reach 9 cm in the year of peak velocity (1).

If puberty is delayed, growth in height may slow considerably. If the delay is not pathologic, the adolescent growth spurt occurs later and growth catches up, with height crossing percentile lines until the child reaches a genetically determined stature.

In children with true precocious puberty (typically defined as breast development before age 8 in girls, growth of the testicles and penis before age 9 in boys), an early growth spurt occurs at a young age and, ultimately, short stature results because of early closure of growth plates. Although precocious puberty is defined as sexual development starting before age 8 in girls or age 9 in boys, some children who develop before age 8 or 9 may be normal. Because onset of puberty is occurring at younger ages in the United States, especially in females, these traditional standards are being re-evaluated.

All organ systems and the body as a whole undergo major growth during adolescence; breasts in girls and genitals and body hair in both sexes undergo the most obvious changes. Even when this process goes normally, substantial emotional adjustments are required. If the timing is atypical, particularly in a boy whose physical development is delayed or in a girl whose development occurs early, additional emotional stress is possible. Most children who grow slowly have a constitutional delay and catch up eventually. Evaluation to exclude pathologic causes and reassurance are needed.

Guidance concerning nutrition, fitness, and lifestyle should be given to all adolescents, with special attention paid to the role of activities such as sports, the arts, social activities, and community service in the adolescent’s life. Relative requirements for protein and energy (g or kcal/kg body weight) decline progressively from the end of infancy through adolescence (see table Recommended Dietary Reference Intakes for Some Macronutrients, Food and Nutrition Board, Institute of Medicine of the National Academies), although absolute requirements increase. Protein requirements for boys age 15 to 18 years are 0.9 g/kg/day and for girls of the same age are 0.8 g/kg/day; mean relative energy requirements for boys age 15 to 18 years are 45.5 kcal/kg and for girls of the same age are 40 kcal/kg.

Sexual maturation generally proceeds in an established sequence in both sexes. The age at onset and rapidity of sexual development vary and are influenced by genetic and environmental factors. Sexual maturity begins earlier today than a century ago, probably because of improvements in nutrition, general health, and living conditions—eg, the average age of menarche has decreased by about 3 years over the past 100 years. The physiologic changes that underlie sexual maturation are discussed in Male Reproductive Endocrinology and in Female Reproductive Endocrinology.

In boys, sexual changes begin with enlargement of the scrotum and testes, followed by lengthening of the penis (see figure Diagrammatic representation of Tanner stages I to V of penis maturation in boys) and enlargement of the seminal vesicles and prostate (1). Next, pubic hair appears (see figure Diagrammatic representation of Tanner stages II to V for development of pubic hair in boys). Axillary and facial hair appears about 2 years after pubic hair. The growth spurt usually begins a year after the testes start enlarging (see figure Puberty—when male sexual characteristics develop). The median age for first ejaculation (between 12½ years and 14 years in the United States) is affected by psychologic, cultural, and biologic factors. First ejaculation takes place about 1 year after penis growth accelerates. Gynecomastia, usually in the form of breast buds, is common among young adolescent boys and usually resolves within several years.

Diagrammatic representation of Tanner stages I to V of penis maturation in boys

Adapted from Figure 1 in Marshall WA, Tanner JM: Variations in the pattern of pubertal changes in boys. Arch Dis Child 45(239):13–23, 1970.

Diagrammatic representation of Tanner stages II to V for development of pubic hair in boys

Adapted from Figure 2 in Marshall WA, Tanner JM: Variations in the pattern of pubertal changes in boys. Arch Dis Child 45(239):13–23, 1970.

Puberty—When Male Sexual Characteristics Develop

Bars indicate normal ranges. No mean is available for change in habitus.

In most girls, breast budding is the first visible sign of sexual maturation, followed closely by the initiation of the growth spurt. Shortly thereafter, pubic and axillary hair appears. Menarche generally occurs about 2 years after onset of breast development and when growth in height slows after reaching its peak. Menarche occurs within a wide range, with most girls in the United States starting their periods at 12 or 13 years (see figure Puberty—when female characteristics develop). The stages of breast growth (see figure Diagrammatic representation of Tanner stages I to V of breast maturation in girls) and pubic hair development (see figure Diagrammatic representation of Tanner stages I to V for development of pubic hair in girls) can be detailed using the Tanner method (2).

If the order of sexual changes is disturbed, growth may be abnormal, and the physician should consider pathologic reasons.

Diagrammatic representation of Tanner stages I to V of breast maturation in girls

From Marshall WA, Tanner JM: Variations in pattern of pubertal changes in girls. Arch Dis Child 44:291–303, 1969; used with permission.

Diagrammatic representation of Tanner stages I to V for development of pubic hair in girls

From Marshall WA, Tanner JM: Variations in patterns of pubertal changes in girls. Archives of Disease in Childhood 44:291–303, 1969; used with permission.

Puberty—When Female Sexual Characteristics Develop

Bars indicate normal ranges.