Hormonal changes in adolescence trigger rapid changes in both height as well as the muscle-fat make-up of the body. The changes are dramatic. Within a few short years, a child will reach his or her adult height and gain almost half of his or her adult weight. While many children are excited about becoming taller, teens feel different about muscle and fat gain.
While the adolescent growth spurt is certainly notable for how much your child grows, it is most amazing how fast the growth happens. It is literally the most rapid physical growth since your kid was 2. At the peak rate, on average, a boy will grow 4 inches a year, while a girl will grow 3.5 inches, with most of the growth coming from lengthening of the torso.
Remember that puberty starts for girls about 2 years earlier than it does for boys, and so it makes sense that we see about a 2-year difference in the timing of growth. This is why there is that brief period of time when all of the girls are a head or so above the boys, roughly around the 5th grade. On average, boys are taller before age 11; between 11 and 13 girls are taller than boys; after 13, boys are generally taller.
What is interesting about the body growth during adolescence is that it is asynchronous – not all parts of the part growth at the same rate and the same time. A teen’s head, hands and feet are the first to growth, followed by growth in arms and legs, followed by torso and shoulder growth. Ever seen a middle school basketball game? Girls and boys are literally tripping over themselves on the breakaway because their feet have grown but not legs, or their rate of airballing goes up because their arms are literally longer than they were at practice two weeks ago. Even at the facial level, often a teen’s nose will grow before other aspects of their face. The delightful awkwardness of a teen is due to the asynchrony in growth. By the end of the growth spurt, the teen will be more proportional, but that is little comfort to a teen who is feeling self conscious about the changes of their body.
Coupled with the changes in height and weight, adolescence also brings about a change in the proportion of one’s body that is muscle and fat. As you might expect, there are some gender differences in these changes. Prior to puberty, girls and boys are pretty similar in muscles and very small differences in body fat. During puberty, however, as individuals grow, muscle tissue grows more rapidly in boys than it does in girls. Conversely, while body fat increases for both boys and girls, it increases more rapidly in girls. Increases in body fat begin prior to puberty and increasing body fat may be a trigger for the start of puberty itself. By the end of puberty, boys have a muscle-to-fat ratio of 3 to 1, while girls have a muscle to fat ration of 5 to 4.
As in other aspects of puberty, how teens perceive the changes will affect their responses to these physical changes of height and weight. If a child perceives gaining muscle as good, he or she will be excited about these changes. Conversely, concerns about fat may lead to different emotions. As parents, it is important to be honest and open with your child, having candid conversations about the changes that are happening.