Adolescent Physical Growth
Written by Joseph Lao, Ph.D.
For the purpose of this discussion, adolescence is assumed to extend from 11-18 years of age. The beginning of adolescence coincides with the onset of puberty (i.e., the process by which the
individual becomes able to procreate). The end of adolescence coincides with the onset of
adulthood (though Jeffrey Arnett suggests there should be another stage between adolescence
and adulthood that he calls "emerging adulthood"). In effect, the body of a child is transformed
into the body of an adult. There is more to adolescence than puberty but puberty is the most
obvious physical benchmark. The physical changes associated with puberty are very well documented, especially in America
by Tanner during the 1960s and 1970s. The ages at which puberty begins and ends varies
across individuals, typically lasting anywhere from 2-6 years. Since female physical growth
tends to outpace male growth females typically display the signs of puberty about two years
earlier (between 11-14 years of age) than males (between 13-15 years of age). African
American females appear to precede Anglo American females in the onset of puberty by an
average of about six months. It is also common for children in rich countries to experience
puberty earlier than children in poor countries. And, there is also a secular trend in place, in
which during the last hundred years, the average age at which children around the world
experience puberty has been slowly declining. For most children, the rate of physical growth during adolescence is the fastest of the entire
lifespan. It is common to find adolescents growing at the rate of 3-6 inches per year. The net
result is that the average American child grows from about 53 inches at 10 years of age to
about 66 inches by 18 years of age, when the growth spurt typically finishes. One parent I know
once exclaimed that she thought she could actually see her son grow as he slept. In addition,
changes in height are correlated with changes in weight. The average weight of children
increases from about 67 pounds, at 10 years of age, to about 134 pounds, at 18 years of age. This gain accounts for about 50 percent of their adult weight. Unlike the preadolescent growth
spurt that occurs between 8-10 years of age, in which females grow faster and taller than
males, during adolescence male growth outpaces that of females. As a result, most males
catch up to and pass females in height and weight during adolescence. Finally, while females
typically reach their maximum height and weight by about 18 years of age, males continue to
grow, reaching their peak height and weight after 20 years of age.
Next to their dramatic increase in height and weight the most obvious physical changes to occur
during adolescene are associated with the diferentiation of the sexes. This consists of the
emergence of secondary sexual characteristics. In males there is an increase in body mass
that is about 50 percent greater than females. This is most evident in their shoulders. The
increase in male muscle mass is about 100 percent greater than in females. In males, the penis
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Adolescent Physical Growth
Written by Joseph Lao, Ph.D.
and testes get larger. There is increased growtih of pubic and public hair. There is also growth
of the male larynx muscles. This causes the male voice to deepen, startig at about 13.9 years
of age and culminating by about 15 years. The onset of phsyical sexual maturity in males is
marked by spermarche (or sometimes called semenarche), or ejaculation. This frequently
occurs in some type of a nocturnal emission ("wet dream") in which a male experiences
ejaculation during an erotic dream. This typically occurs around 13 years of age.
Although females also experience a mini growth spurt during adolescence, female bodies
change in different ways than males. Much of the weight gained by females is due to a 25
percent increase in body fat. This is about twice as much as males. Girls get wider hips during
adolescence. They also get larger breasts, and pubic hair grows. Brain Growth
While the human brain reaches approximately adult size by about 12 years of age, it is not yet
completely mature. First, it is important to bear in mind that the human brain continues to adapt
to environmental conditions, especially through experience, throughout our lifetime. Those
parts of the brain that are used more tend to grow more than those that are underutilized. This
means that as long as we are interacting with our environment, and especially as long as we
are learning, our brain continues to grow. Second, the last part of the human brain to fully
mature is the frontal lobe. This is the part of the brain responsible for planning, impulse control,
and the organization of voluntary behavior. Although development of this part of the brain
continues during adolescence, the myelination process (in which myelin sheaths wrap
themselves around the axons of neurons) continues unti our late thirties. As a result, the frontal
lobe gradually continues to increase it's capacity to inhibit impulsive behavior as we mature. Some researchers have noted that this ability is one of the greatest distinctions between
adolescents and adults. How Can I Nurture My Adolescent's Physical Growth?
The principles of physical growth are similar across the lifespan. The factors that influence
adolescent growth are similar (though not identical) to those influencing growth during other
periods of development. The most important thing you can do is provide a diet of healthy
nutritious foods. (To learn more about nutrition click here). The rapidly growing adolescent
body depends on vitamins and nutrients contained in healthy foods. Unfortunately, adolescents
who are busy learning about so much of what the world has to offer do not generally think about
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Adolescent Physical Growth
Written by Joseph Lao, Ph.D.
the most nutritious substances to consume. Parents can help tremendously by reinforcing
healthy eating habits. It is important for adolescents to get plenty of physical and mental exercise. It is common for
teenagers to join school athletic teams. Because of their greater height, strength, and
endurance, boys tend to gravitate toward rough and tumble sports, especially football, wrestling,
and basketball. Girls tend to prefer less physically demanding sports. It is also common to find
adolescents engaged in regular exercise at home, especially boys. This may involve running or
weight lifting. Athletic activity should be encouraged. Get your child involved in some sort of
school team, and cheer them on, e.g., by attending their games. This means more to most
teenagers than most parents would imagine.
On the other hand, it is also important for adolescents to get enough rest. In contrast to the
increasingly busy lifestyle of today's adolescent, scientific research has revealed that the
average adolescent is not getting enough sleep. This is in part because they typically need
about 9 1/4 hours of sleep but are lucky to get eight hours. This affects their moods
(adolescents, and adults, tend to get grumpy when they don't get enough sleep), and their
academic performance. One study found that allowing adolescents to start their school day one
hour later resulted in significant improvements in their academic performance. 3/3