17 Physical Development During Adolescence

Physical Development during Adolescence

Adolescence Defined

Adolescence is often characterized as a period of transformation, primarily, in terms of physical, cognitive, and social-relational change. Adolescence is a developmental stage that has been defined as starting with puberty and ending with the transition to adulthood (approximately ages 10–20). Adolescence has evolved historically, with evidence indicating that this stage is lengthening as individuals start puberty earlier and transition to adulthood later than in the past. Puberty today begins, on average, at age 10–11 years for girls and 11–12 years for boys. This average age of onset has decreased gradually over time since the 19th century by 3–4 months per decade, which has been attributed to a range of factors including better nutrition, obesity, increased father absence, and other environmental factors (Steinberg, 2013). Completion of formal education, financial independence from parents, marriage, and parenthood have all been markers of the end of adolescence and beginning of adulthood, and all of these transitions happen, on average, later now than in the past. In fact, the prolonging of adolescence has prompted the introduction of a new developmental period called emerging adulthood that captures these developmental changes out of adolescence and into adulthood, occurring from approximately ages 18 to 29 (Arnett, 2000). (46)


Adolescence begins with puberty. While the sequence of physical changes in puberty is predictable, the onset and pace of puberty vary widely. Several physical changes occur during puberty, such as adrenarche and gonadarche, the maturing of the adrenal glands and sex glands, respectively. Also during this time, primary and secondary sexual characteristics develop and mature. Primary sexual characteristics are organs specifically needed for reproduction, like the uterus and ovaries in females and testes in males. Secondary sexual characteristics are physical signs of sexual maturation that do not directly involve sex organs, such as development of breasts and hips in girls, and development of facial hair and a deepened voice in boys. Girls experience menarche, the beginning of menstrual periods, usually around 12–13 years old, and boys experience spermarche, the first ejaculation, around 13–14 years old.

During puberty, both sexes experience a rapid increase in height (i.e., growth spurt). For girls this begins between 8 and 13 years old, with adult height reached between 10 and 16 years old. Boys begin their growth spurt slightly later, usually between 10 and 16 years old, and reach their adult height between 13 and 17 years old. Both nature (i.e., genes) and nurture (e.g., nutrition, medications, and medical conditions) can influence height.

Because rates of physical development vary so widely among teenagers, puberty can be a source of pride or embarrassment. Early maturing boys tend to be stronger, taller, and more athletic than their later maturing peers. They are usually more popular, confident, and independent, but they are also at a greater risk for substance abuse and early sexual activity (Flannery, Rowe, & Gulley, 1993; Kaltiala-Heino, Rimpela, Rissanen, & Rantanen, 2001). Early maturing girls may be teased or overtly admired, which can cause them to feel self-conscious about their developing bodies. These girls are at a higher risk for depression, substance abuse, and eating disorders (Ge, Conger, & Elder, 2001; Graber, Lewinsohn, Seeley, & Brooks-Gunn, 1997; Striegel-Moore & Cachelin, 1999). Late blooming boys and girls (i.e., they develop more slowly than their peers) may feel self-conscious about their lack of physical development. Negative feelings are particularly a problem for late maturing boys, who are at a higher risk for depression and conflict with parents (Graber et al., 1997) and more likely to be bullied (Pollack & Shuster, 2000). (47)

Physical Development during Adolescence (continued)

The Brain: Basic Facts

The frontal cortex, the area of the brain responsible for rational thinking, is still developing during adolescence. Adolescents differ from adults in the way they behave, solve problems, and make decisions. Recent research shows that there is a biological explanation for this difference; the brain continues to develop during adolescence and even into early adulthood.

Brain Development: The Amygdala and the Frontal Cortex

The amygdala and the frontal cortex are two key regions of the brain that develop at different times. The amygdala, which processes stress and other emotions, and is responsible for instinctual reactions like fear and aggressive behavior, matures early.

On the other hand, the frontal cortex, the area of the brain responsible for judgment, self-control, emotional regulation, rational thought, goal setting, morality, and understanding consequences, is not yet fully developed in teenagers. In fact, this area of the brain develops quite dramatically during adolescence and into the mid-20s.

What Does This Mean for Adolescents?

Pictures of the brain in action show that adolescents’ brains function differently from those of adults when making decisions and solving problems. Adolescents’ actions are guided more by the amygdala and less by the frontal cortex. That means that teens’ responses to situations are rooted in emotion rather than rationality. In other words, the last part of the brain to fully develop is one of the most important—it’s the area that gives people the ability to make rational decisions.

Because the part of the brain that helps us think before we act isn’t fully developed until adulthood , in stressful situations or when faced with difficult decisions, teens are more likely to:

  • Think one thing and feel another
  • Act from impulses that differ from thoughts or feelings
  • Misread or misinterpret social cues and emotions
  • Engage in risky or inappropriate behavior

How Can Adults Help?

There are several ways adults can help teens make healthy choices. Adolescents’ brains go through a “use-it-or-lose-it” pruning system: brain cells and neural connections that get used the least get pruned away and die off, whereas those that get used the most become stronger.

To help teens make healthy choices, walk them through the decision making process before they encounter risky situations. This will help them to make life-impacting decisions with less stress. Teens who undergo learning and positive experiences help build complex, adaptive brains.

Strategies to Support Healthy Adolescent Brain Development

  • Encourage teens to have healthy lifestyles and offer opportunities for positive experiences.
  • Provide meaningful opportunities for teens to exercise logic and apply analytical and decision making skills to build up those brain functions.
  • Encourage teens to take healthy risks. Taking such risks will help to develop a stronger frontal cortex, effectively giving the teen more valuable life skills.
  • Allow teens to make mistakes so that they can learn from them. (48)

Physical Development during Adolescence (continued)

Nutrition and Activity

Adolescents may be ready to make decisions about their body and health. Making healthy decisions about what to eat and drink, how active they are, and how much sleep to get are important decisions that can either promote or hinder health. Unfortunately, many teens do not make healthy decisions, partly due to the frontal cortex still developing and partly due to the culture in which we live. In the United States, 20% of individuals between the ages of 12 and 19 are obese. If you ever have the opportunity to watch the documentary, “Fed Up.” It powerfully shows how we are failing our adolescents in terms of healthy eating.

Healthy Eating

Teens need to be taught how to make healthy eating choices. Here are some healthy eating tips that teens should know:

  • Try to limit foods like cookies, candy, frozen desserts, chips, and fries, which often have a lot of sugar, unhealthy fat, and salt.
  • For a quick snack, try recharging with a pear, apple, or banana; a small bag of baby carrots; or hummus with sliced veggies.
  • Don’t add sugar to your food and drinks.
  • Drink fat-free or low-fat milk and avoid sugary drinks. Soda, energy drinks, sweet tea, and some juices have added sugars, a source of extra calories. The 2015-2020 Dietary Guidelines recommend getting less than 10 percent of your daily calories from added sugars.

In addition to making smart food choices, it is also important to know that the nutritional needs of adolescents are unique. Many teens need more of these nutrients:

  • Calcium , to build strong bones and teeth. Good sources of calcium include fat-free or low-fat milk, yogurt, and cheese.
  • Vitamin D , to keep bones healthy. Good sources of vitamin D include orange juice, oranges, tuna, and fat-free or low-fat milk.
  • Potassium , to help lower blood pressure. Good sources of potassium include bananas and baked potatoes with the skin.
  • Fiber , to help stay regular and feel full. Good sources of fiber include beans and celery.
  • Protein , to give you energy and help you grow strong. Good sources of protein include peanut butter, eggs, tofu, legumes (lentils and peas), and chicken, fish, and low-fat meats.
  • Iron , to help you grow. Red meat contains a form of iron that your body absorbs best. Other good sources of iron include spinach, beans, peas, and iron-fortified cereals. You can help your body absorb the iron from these foods better when you combine these foods with vitamin C, like an orange.

Physical Activity

Physical activity should be part of teenagers’ daily life, whether they play sports, take physical education (PE) classes in school, do chores, or get around by biking or walking. Regular physical activity can help teenagers manage their weight, have stronger muscles and bones, and be more flexible.

Aerobic Versus Lifestyle Activities

People, regardless of age, need to be physically active for at least 60 minutes a day. Most of the 60 minutes or more of activity a day should be either moderate or intense aerobic physical activity. Everyone should include intense physical activity at least 3 days a week. Examples of aerobic physical activity or activity that makes you breathe harder and speeds up your heart rate, include jogging, biking, and dancing.

For a more moderate workout, brisk walking, jogging, or biking on flat streets or paths all work. To pick up the intensity, individuals can turn a walk into a jog, or jog into a run and including hills to the walk, jog, or bike ride. We don’t have to do 60 minutes a day all at once to benefit from the activity. Teens can download fitness applications onto their computer, smartphone, or other mobile device to help keep track of how active they are each day. (49)

Sleep Needs

Sometimes it’s difficult for teens to get enough sleep, especially if they have jobs, help take care of younger brothers or sisters, or are busy with other activities after school. Like healthy eating and getting enough physical activity, getting enough sleep is important for staying healthy.

Everyone needs enough sleep to do well in school, work, drive safely, and fight off infection. Not getting enough sleep may lead to moodiness and irritability. While more research is needed, some studies have shown that not getting enough sleep may also contribute to weight gain. Individuals between 13 and 18 years old should get 8 to 10 hours of sleep each night.

The amount of sleep you need changes as you age. Children need more sleep than adults. The American Academy of Sleep Medicine and the Sleep Research Society recommend:

Age Group Recommended Hours of Sleep Per Day
Infant 4-12 months 12-16 hours per 24 hours (including naps)
Toddler 1-2 years 11-14 hours per 24 hours (including naps)
Pre-school 3-5 years 10-13 hours per 24 hours (including naps)
School Age 6-12 years 9-12 hours per 24 hours
Teen 13-18 years 8-10 hours per 24 hours
Adult 18-60 years 7 or more hours per night

Habits to Improve Your Sleep

There are some important habits that can improve your sleep health:

  • Be consistent. Go to bed at the same time each night and get up at the same time each morning, including on the weekends.
  • Make sure your bedroom is quiet, dark, relaxing, and at a comfortable temperature.
  • Remove electronic devices, such as TVs, computers, and smart phones from the bedroom.
  • Avoid large meals, caffeine, and alcohol before bedtime.
  • Avoid tobacco/nicotine.
  • Get some exercise. Being physically active during the day can help you fall asleep more easily at night.

What about Sleep Quality?

Getting enough sleep is important, but good sleep quality is essential. Signs of poor sleep quality include feeling sleepy or tired even after getting enough sleep, repeatedly waking up during the night, and having symptoms of sleep disorders (such as snoring or gasping for air). Better sleep habits may improve the quality of your sleep. (50)


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Child and Adolescent Psychology Copyright © by Lumen Learning is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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