466 Adolescent Health
characteristics). Adolescent medicine specialists have pro-
moted the routine use of Tanner staging. Clinically, a 12-year-
old girl at Stage 1 will have very different concerns and health
risks than 12-year-old girls at Stage 4 or 5.
Tanner staging is also valuable for research purposes. For
example, a study of panic attacks among sixth- and seventh-
grade girls reported striking differences in the incidence
of panic attacks as a function of sexual maturity, but no
differences due to chronological age (Hayward, Killen, &
Hammer, 1992). Traditionally, Tanner stage is rated by physi-
cians and based on physical examination. Fortunately, Litt
and her colleagues (Duke, Litt, & Gross, 1980) found that
teenagers can rate themselves with considerable accuracy,
and this method has been employed in more recent research.
While accuracy appears to be more problematic with abnor-
mal samples (e.g., adolescents with growth retardation), self-
ratings seem to be acceptably reliable and valid with normal
populations (see Finkelstein et al., 1999).
It is impossible to overemphasize the extent of physical
change that occurs during the relatively brief period of pu-
berty. Major endocrine changes are associated with the onset
of puberty, with three distinct changes in the hypothalamic-
pituitary unit and (typically) increased secretion of sex
hormones from the adrenal gland. Other changes occur in
insulin secretion, growth hormone, and somatomedins. While
it seems evident that substantial increases in hormonal levels
(especially testosterone) would be related to increased sexual
urges and to aggression, the effects on behavior are not yet
well understood. What is clear is that teenagers experience
major biochemical and skeletal changes during puberty.
During childhood (age 5 to 10 years), the average child
grows 5 cm to 6 cm per year. In contrast, during the average
adolescent growth spurt (24 to 36 months), girls grow 23 cm
to 28 cm, and boys grow 26 cm to 28 cm taller„a growth rate
of 10 cm to 11 cm per year, twice that of childhood. For both
genders, pubertal growth accounts for 20% to 25% of “nal
adult height. Weight growth is even more dramatic, account-
ing for about 50% of ideal adult body weight.
Other physical changes accompany rapid increase in
height and weight. Adolescents grow in a concentric fashion,
with their extremities (heads, hands, and feet) reaching adult
size “rst, followed by their limbs and “nally their torsos. This
accounts for the •ganglyŽ appearance of many teenagers,
who seem to be •all arms and legs.Ž Teenagers also experi-
ence signi“cant changes in body composition. Percentage
of body fat changes from about 15% in prepubertal girls
(comparable to that of prepubertal boys) to 27% by Tanner
Stage 4, along with pelvic remodeling and the emergence of
breasts and hips. In contrast, lean body mass increases in
boys to about 90% at maturity, largely re”ecting in-
creased muscle mass. During puberty, boys also experience a
sevenfold increase in the size of the testes, epididymis, and
prostate, while the phallus usually doubles in size. Given
these signi“cant changes in body size and shape, adolescent
medicine clinicians joke that young teenagers are obsessed
with their hair because it is the only part of their bodies that
they recognize from one month to the next. Indeed, it is re-
markable that adolescents are able to remain suf“ciently
coordinated to be able to play a variety of sports.
Spermarche,the onset of seminal emission, appears to be
an early pubertal event for boys (median age 13.4 years) al-
though there is considerable variation (range 11.7 to 15.3). It
precedes peak height velocity in most boys and may occur
with no evidence of pubic hair development. Some sperm are
usually present in the ejaculate by Tanner Stage 3 but fertility
is generally not reliable until Tanner Stage 4.
Menarche,the onset of a girl•s monthly period, has been
studied much more extensively than spermarche, presumably
because it is a discrete and salient event unlike the more
subtle sexual development of boys. American girls experi-
ence menarche at about 12.3 years (with normal variation
from 9 to 17 years). A secular trend has been observed over
the last century, with a gradual decrease in the age of menar-
che both in the United States and in European countries. This
decrease is hypothesized to re”ect improved nutrition and
appears to have leveled out with little decrease from 1960 to
the present.
For individual girls, the age of menarche is a function of
factors such as race, socioeconomic status, heredity, nutrition,
culture, and body composition. For example, menarche tends
to occur at a later age in rural families, in larger families, and
at higher altitudes. Also, amenorrhea (the absence or cessa-
tion of periods) is commonly found among girls who are un-
derweight and/or have an unusually low percentage of body
fat, such as athletes or ballerinas who train intensively.
Despite the apparent stability of the age of menarche,
however, there have been reports that the onset of secondary
sexual characteristics is occurring at an earlier age for many
American girls. After observing breast development in a
number of young female patients (age 7 to 9 years), a pedia-
trician launched a large study of 17,000 girls. This investiga-
tion con“rmed the clinical observation, and it does appear
probable that American girls are developing secondary sex-
ual characteristics at an earlier age than they did in the 1960s,
even through the age of menarche remains unchanged
(Herman-Giddens et al., 1997). This “nding has prompted in-
tense speculation regarding the reason for the change, with
the most popular culprit hypothesized to be the increased fat
in the American diet: It may be that even mild obesity is pro-
viding the trigger for very early sexual development. Alterna-
tive hypotheses focus on environmental changes, including
increased hormones in milk and other animal products