Physical Changes

Adolescence is the life stage between childhood and adulthood. Its age limits

are not clearly specified, but it extends roughly from age twelve to the late

teens, when physical growth is nearly complete. Puberty, a term often confused

with adolescence, occurs at the end of childhood and lasts from two

to four years. It is the period of adolescence during which an individual

reaches sexual maturity.

Human beings grow most rapidly at two times during their lives: before

they are six months old and during adolescence. The second period of accelerated

growth is often referred to as the adolescent growth spurt. Adolescents

grow both in height and weight, with the increase in height occurring

first. As they gain weight, the amount and distribution of fat in their bodies

changes, and the proportion of bone and muscle tissue increases. In girls,

the adolescent growth spurt usually begins between the ages of nine and

eleven and reaches a peak at an average of twelve and a half years. Then

growth slows and usually ceases completely between the ages of fifteen and

eighteen. The growth spurt in boys generally begins about two years later

than it does in girls and lasts for a longer time. It begins between the ages of

eleven and fourteen, reaches a peak at about age fifteen, and slowly declines

until the age of nineteen or twenty.

The teenager’s body grows at differing rates, so that at times adolescents

look a bit awkward. Big feet and long legs are the early signs of a changing

body, but even these changes do not occur at the same time. First the hands

and feet grow, then the arms and legs; only later do the shoulders and chest

grow to fit the rest of the developing body. Changes in body proportion become

obvious. The trunk widens in the hips and shoulders, and the waistline

narrows. Boys tend to broaden mostly in the shoulders, girls in the hips.

Puberty is chiefly characterized by sexual development. Sexual development

can be best understood by examining the maturation of primary and

secondary sex characteristics. Primary sex characteristics are the physiological

features of the sex organs. For males, these organs are the penis and the

testes; for females, they are the ovaries, uterus, clitoris, and vagina. Secondary

sex characteristics are not directly related to the sexual organs but nevertheless

distinguish a mature male from a mature female. Examples of secondary

sex characteristics are the male beard and the female breasts.

In girls, the onset of breast development is usually, but not always, the first

sign that puberty has begun. This typically occurs between the ages of ten

and eleven but can occur as late as ages thirteen and fourteen. There is simultaneous

development of the uterus and vagina, with enlargement of the

labia and clitoris. Menarche (the first menstrual period), although perhaps

the most dramatic and symbolic sign of a girl’s changing status, occurs relatively

late in puberty, after the growth spurt has reached its peak velocity.

The first menstrual periods tend to be irregular, and ovulation (the release

of a mature egg) does not usually begin until a year or so after menarche.

Onset age of menarche has decreased as body weight has increased in the

modern era, with girls on average reaching menarche at ten and a half to

eleven years of age.

The first noticeable change in boys is usually growth of the testes and

scrotum. The growth of the genitals begins, on average, about the age of

twelve and is completed, on average, by about the age of fifteen. Boys generally

become capable of ejaculation about a year after the penis begins to

grow. These first emissions may occur as a result of nocturnal emissions, the

ejaculation of semen during sleep. Nocturnal emissions are a normal phase

of development and are frequently caused by sexual excitation in dreams or

by some type of physical condition, such as a full bladder or even pressure

from pajamas.

As the bodies of adolescents become more adult, their interest in sexual

behavior increases sharply. They must learn the necessary behavior to satisfy

that interest, and they must face the issue of a mature gender identity. This

includes the expression of sexual needs and feelings and the acceptance or

rejection of sex roles. The onset of dating and the beginning of physical intimacies

with others can provoke frustration and anxiety. As this unfamiliar

territory is explored, the adolescent is often very underinformed and overly

self-conscious. Conflicting sexual values and messages are frequently encountered,

accentuating the problem of integrating sexual drives with other

aspects of the personality.