This section will identify the typical, average ages when youth reach certain developmental milestones; but, it is important to keep in mind that individual youth will develop according to their body's own timetable. As such, a youth's development may not always follow these averages but their development may still be considered healthy and normal. If parents have concerns about their child's growth or development, they should discuss these concerns with their child's health care provider.
Because the rate of physical development is so varied during adolescence, it often becomes a source of difficulty and discomfort for youth. Some teens will develop more slowly than their peers. As a result, they may feel self-conscious about their bodies' lack of maturity, relative to their peers. They may even feel disappointed or resentful they are not receiving the same kind of attention their more physically mature friends seem to enjoy. This can lead to feelings of frustration because their bodies aren't maturing as fast as they would like, or they may worry that something might be wrong with them.
Conversely, some teens may mature more quickly than their peers. This earlier development may also cause feelings of frustration and self-consciousness. These teens may be teased about their changing bodies and they may receive more attention than they desire, which can cause them to feel uncomfortable and conspicuous. This can be especially true for teen girls as the overt admiration of the female body is generally considered an acceptable practice in our culture. A young female teen may not be emotionally prepared to be viewed and admired in a sexual manner. Parents may wish to assist their daughters to determine the limits of what is respectful and acceptable to them, and to develop strategies for handling situations that make them feel uncomfortable. Teenage boys who develop sooner than their male peers may have an easier time because although physical prowess in males is respected and admired, it is less common for them to receive unwanted public attention.
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Changes in height and body composition
During adolescence, most growth in height generally occurs during one, single growth period, or "growth spurt." Girls normally start their growth spurt between the ages of 8 and 13 years, with the most rapid growth occurring between the ages of 10 and 13 years. Girls reach their adult height between the ages of 10 and 16 years. Boys tend to begin their growth spurt a bit later than girls. On average, guys start their growth spurt between the ages of 10 and 16 years, with the most rapid growth occurring between the ages of 12 and 15 years. Boys reach their adult height between the ages of 13 and 17. Even though guys reach their adult height later than girls, young men grow to become taller than their female peers. The average height of adult women is 5'5", and the average height of adult men is 5'10". Several factors can influence potential height such as genetics and nutrition, as do certain medical conditions and medications that interfere with digestion and appetite.
During adolescent growth spurts, the arms and legs also lengthen and eventually become proportional to the rest of their body. However, teens may suddenly feel awkward and uncoordinated during this time because growth does not always occur at a perfectly proportional rate. Their limbs may become longer or shorter relative to the rest of their bodies and it may confuse or frustrate young teens to inhabit a body that no longer seems familiar.
Besides significant changes in height, adolescents also experience changes in body composition; i.e., the ratio of body fat to lean muscle mass. Teen boys' lean muscle mass greatly increases during adolescence due to the rising levels of male hormones, such as testosterone, that cause an increase in muscle mass. In general, boys' straight-lined, square bodies become broader at the shoulders and more tapered at the waist, forming the familiar triangular shape of adult males. Their arms and legs will become more muscular and bulkier. However, factors such as heredity, nutrition, and muscle-building exercise can influence muscular development. If adolescents play sports, lift weights, or routinely workout in other ways, they are more likely to gain muscle mass. Many teen boys may feel self-conscious about their body if they believe they are not building enough muscle in comparison to their friends and classmates.
Teen girls continue to develop muscle mass while also adding body fat. During adolescence, girls' percentage of body fat will increase, relative to muscle mass. This additional fat is deposited in her body's midsection (hips, buttocks, and chest). Girls' straight-lined, square bodies become wider and broader at the hips, buttocks, and chest, forming the familiar hour-glass shape of adult females. Often, teen girls feel uncomfortable or upset during this growth phase because of the increase in body fat. In some rare cases, an Eating Disorder may develop as a result. For information about the early signs of an Eating Disorder please refer to the topic center on eating disorders. Girls should be encouraged to view this change to their body composition in a positive light: as yet another indication they are becoming young women. While girls may feel "fat" during this maturation process, it may be helpful for them to understand that some additional body fat is necessary for women to have healthy pregnancies and in order to nurse babies.
While their bodies are changing and growing it's particularly important for teens and older adolescents to maintain a healthy lifestyle that includes a balanced, nutrient-rich diet, with plenty of exercise, and adequate, restful sleep. Maintaining this healthy balance helps to prevent medical problems such as obesity and diabetes and also protects mental health by creating a healthy and confident self-image.