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AOSSM 2022 Annual Meeting Recordings - no CME
Pubertal Growth Spurt: What Changes in Boys and Gi ...
Pubertal Growth Spurt: What Changes in Boys and Girls
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Good afternoon. My name is Mark Reederer. Thank you, Dr. Vojtis, for that introduction. And as he had said, I am a non-operative pediatric sports medicine physician at the University of Michigan. I would like to thank Dr. Vojtis for inviting me to take a part of today's discussion with such a distinguished panel of speakers today, and to certainly enjoy this magnificent hotel. I would be happy to come back to any AOSSM and speak. The title of my first presentation is Pubertal Growth Spurt, What Changes in Boys and Girls? I have no financial relevant disclosures. So today's learning objectives, to understand the physical changes during normal pubertal growth spurt in adolescents, recognize the differences in the pubertal changes between boys and girls, identify the influence of obesity, race, and physical activity on pubertal onset, and understand the role of puberty has on the young athlete training. So why is this talk important? Prior to puberty, there are little differences between the athletic performance in boys and girls. During puberty, there are dramatic changes with significant differences between boys and girls. And lastly, these differences can improve performance, however, also pose injury risk. Puberty is the physiologic process where adolescents undergo dramatic changes in physical growth and sexual maturation. There are dramatic changes in body size, shape, and composition, and it is sexually dimorphic. So when does puberty start? There's not one single mechanism that has been identified. There are various genetic and environmental factors. Anywhere from 50% to 80% of pubertal timing is from parental history. Obesity, low socioeconomic status, chronic stress, and poor nutrition, as seen in anorexia nervosa and REDS, which stands for relative energy deficiency in sport, are all linked to delayed puberty. Secular trends, which are temporal changes in height and weight, have shown decreasing age of onset of puberty during the 20th century, however, this has recently stabilized. In girls, the onset of puberty is around 11, however, as we'll talk later in this presentation, that that does vary with ethnicity and race. And in boys, around 13. But there is certainly a wide range. So Tanner staging is an established means of assessing pubertal development by physical examination. In boys, the assessment is by testicular size and pubic hair development, and the onset is essentially when testicular size enlarges in boys. The growth spurt occurs during Tanner stage four. In girls, breast bud and pubic hair development are assessed, and in girls, the onset is with breast bud development. Growth spurt occurs during Tanner stages two and three. This is a diagram of the pubertal Tanner staging. Again, it is classified in boys with testicular enlargement and pubic hair development, and in girls, breast bud development and pubic hair development, too. And as a reminder, in girls, the peak height velocity or the growth spurt occurs anywhere between Tanner stage two and three, and in boys, stage four. So the growth spurt is a landmark physical change during puberty. Just prior to this, there is a nadir, or pre-adolescent dip, and it accounts for about 15 to 20% of the adult height. In girls, as I just mentioned, it occurs anywhere between Tanner stage two and three. The peak height velocity is about nine centimeters per year, and the average age of completion is 15. In boys, this occurs during Tanner stage four, and the peak height velocity is about 10.3 centimeters per year, and the average age of completion is 17. The greater peak height velocity and longer pre-pubertal growth results in greater height, adult height difference between boys and girls. This is a diagram of both girls and boys, girls being on the left, boys being on the right of their peak height velocity, each line representing a different growth percentile. And as you can see, the peak height velocity in girls is just after about 11, and in boys, just after 13. This is a table, again, summarizing the growth spurt and when the mean age at takeoff and peak height velocity are in samples of European and North American adolescents. We'll get to this a little bit later in the talk about how ethnicity changes the onset of puberty, but as you can see in African American girls, there's earlier takeoff as well as peak height velocity than North American and Caucasian samples, and the same goes for boys, but not as dramatic. So where does the growth occur? This diagram shows height, sitting height, and leg length, and the distribution of growth, and what I'd like you to do is focus in on the puberty portion of this graph. So linear growth first starts in the lower extremities and is followed by growth in the torso and upper extremities. Frequently, a lot of parents come to see me and ask, well, how tall is Johnny going to be? And you can actually calculate that with some degree of certainty and accuracy through the mid-parental height. This is for both girls and boys. It's essentially taking, for girls, the father's height and mother's height and subtracting 13 centimeters and getting the average of the two, and for boys, you would add 13 centimeters. So let's go into how different hormones affect bone, muscle, fat, and ligament growth during puberty. So growth hormone and insulin-like growth factor are fundamental regulators of longitudinal bone growth. The precise mechanism of how these two hormones, their effect on the epiphyseal growth plate is unknown. We do know that growth hormone recruits resting chondrocytes into a proliferative state and stimulates local IGF-1. Once activated, chondrocytes become responsive to IGF-1, and IGF-1 acts mainly in the hypertrophic zone, enabling chondrocyte proliferation. Estrogen and testosterone also have direct effects on bone formation during the growth spurt. They promote deposition of bone material, accounting for about 90% of peak skeletal mass by 18 in adolescence. Estrogen receptors are located throughout the growth plate and activates the growth hormone IGF-1 axis. In early puberty, low doses of estrogen stimulate chondrocyte growth, seen in the proliferative zone, and higher dose estrogens seen in late puberty are responsible for the epiphyseal fusion. Testosterone may also contribute to bone formation by indirect effects on chondrocytes through its effect on IGF-1 receptors and accounts for larger skeletal size in boys. Testosterone reduces bone resorption and increases periosteal deposition of bone. During peak height velocity, higher rates of distal radius and ulna fractures are seen in children between 10 and 14 than in prepubertal or young adults, and we consider this the transient adolescent osteopenia. Adolescents with delayed puberty or secondary amenorrhea may fail to accrue bone mineral normally and have reduced bone mineral density as adults, as we see in the female athlete triad or also known as the relative energy deficiency in sport. Current recommendations for calcium and vitamin D in growing adolescents are about 1,200 milligrams of calcium per day and anywhere from 600 to 4,000 international units of vitamin D per day. We typically recommend the higher dose of 4,000. So at the epiphyseal growth plate, bone elongation during the pubertal growth spurt occurs at this location. Gonadal steroids, growth hormone IGF-1 influence proliferation and differentiation of chondrocytes at the epiphyseal growth plate. What about muscle growth during puberty? Muscle mass grows during puberty with more pronounced in boys than in girls due to the androgen effects. Testosterone causes significant increases in lean muscle mass along with loss of adipose tissue. IGF-1 plays an important role in muscle growth through stimulation of glycogen accumulation and transfer of amino acids for protein synthesis. Girls reach a plateau in muscle strength by about 15 and boys demonstrate an acceleration of muscle strength around 13. In terms of ligament growth during puberty, IGF-1 promotes growth of connective tissue through the formation of collagen. With regards to fat development during puberty, fat mass and fat-free mass increases in both boys and girls during their peak height velocity. Fat accumulation increases twice as much in girls than in boys. Girls during Tanner stage 4 and 5 will gain fat mass proportionally more concentrated in the lower body and girls will have 25% body fat at the end of puberty compared to boys that have about 13%. Significant weight gains are obtained during puberty from bone fat and muscle. Approximately 50% of your adult body weight is gained. In boys, the peak weight velocity occurs during peak height velocity and it is about 9 kilograms per year. And for girls, peak weight velocity trails peak height velocity by about six months, which is about 8.3 kilograms per year. With regards to flexibility in puberty, girls have greater flexibility compared to boys as we all know. Flexibility tends to decrease in boys leading to about 14 to 16 years of age. Flexibility tends to increase in girls between 10 to 13 and plateaus 14 to 15. And skeletal growth typically occurs before musculotendinous growth, especially in males. We've all heard the adage that bones grow faster than muscles. So obesity is associated with earlier pubertal development. These children are tall for their age and more advanced in their Tanner staging. Epidemiologic studies in the U.S. have shown black girls with higher BMIs are more likely to have early menarche compared to white girls. And this may be associated with higher leptin levels seen in blacks. Leptin serves as a metabolic signal for puberty to progress. But that association is not as strong as in boys. This is a diagram showing and outlining leptin's influence on the hypothalamus, pituitary, gonads, adrenals, and the epiphyseal growth plate. With regards to ethnicity and puberty, black girls tend to have earlier onset of puberty than white girls. They have earlier peak height velocity, age of menstruation. They tend to be heavier and taller. Additionally, Mexican-American girls are almost two times as likely to have early menarche compared to white girls. But in comparison, Asians are almost a little over one and a half times likely than males to mature later than 14. This is a table summarizing the mean ages at onset of sexual, stages of sexual maturation samples from European and North American adolescents. Just looking at, again, highlighting that girls' breast stages for African-American girls compared to Caucasian and North American are a little bit earlier, as well as Mexican-American. And that also holds true for boys, too, as well. Worldwide poverty-related malnutrition is the single most cause of growth retardation and delayed pubertal development in the US. Delayed pubertal development is commonly from low energy availability. So what's physical activity's role with the development of puberty? Marked undernutrition combined with heavy training and competition can suppress growth, maturation, and delayed pubertal development. Weight-controlled sports, such as gymnastics, performing arts, wrestling, and endurance sports are at risk for delays in pubertal growth. The link between physical activity and delayed puberty is not entirely clear, however. There are well-documented delays in growth and sexual maturation in female gymnasts. Female gymnasts are shorter. They have less body fat. They have slower growth velocities. Female gymnasts had average age of menarche at 15.6 years of age versus 13.2 in controls in one study. Gymnasts have significantly delayed skeletal age also compared to age-matched swimmers. In boys, the link between high energy-demanding sports and pubertal onset is less clear. Distant runners in boys showed no difference in height velocity compared to age-matched controls. One study of almost 500 high school male wrestlers showed no statistically significant differences in the slope values for height and age-matched controls. And lastly, it's difficult, again, to make this link. These sports select desirable anthropometric traits of these boys and girls. So in summary, the physical changes between boys and girls, boys have later onset of puberty than girls. They have a higher peak velocity than girls. Their growth spurt lasts longer than girls. Their shoulders broaden where girls' hips widen. And they have increased muscle mass and strength with less adipose tissue distribution than girls. So in conclusion, puberty in the young athlete is characterized by rapid changes in growth, size, potty composition. The pubertal growth spurt occurs sooner and is shorter in girls and later and longer in boys. Obesity, physical activity, nutrition, race, ethnicity all have influences on the onset of puberty. And lastly, clinicians must be mindful of physical changes in young athletes during their puberty growth spurt. And these are my references. Thank you. Thanks, Mark. That was a great talk to start things off. But one of my favorite questions for pediatricians is, what are growing pains, Mark? We always hear that used and you get interesting answers, but what's your best explanation for that? Is it the bones stretching our muscles and tendons? What is it? So that's a really good question. I do see a lot of kids in my clinic who are usually younger kids, school-aged children who have leg pains. And I don't know if anybody really understands what the mechanism of that is. It could be from changes in vitamin D, could be vitamin D deficiency, could be stretch of periosteum where the nerves are. Usually it's bilateral, occurs at night, maybe worse later in the day, alleviates with NSAIDs. But I don't know if anybody really understands the mechanism of what causes growing pains. Fair enough. I was going to say guys my age shouldn't be experiencing that. Okay. All right. Thanks, Mark.
Video Summary
In this video, Dr. Mark Reederer, a non-operative pediatric sports medicine physician at the University of Michigan, discusses the physical changes that occur during puberty and how they differ between boys and girls. He explains that puberty is a physiologic process characterized by dramatic changes in physical growth and sexual maturation, and it is sexually dimorphic. Dr. Reederer discusses the onset of puberty, which is influenced by genetic and environmental factors, and the differences between boys and girls in terms of physical changes such as height, weight, muscle mass, and fat distribution. He also discusses the role of hormones, such as growth hormone, insulin-like growth factor, estrogen, and testosterone, in bone, muscle, fat, and ligament growth during puberty. Dr. Reederer highlights the importance of factors such as obesity, race, and physical activity in influencing pubertal onset. He concludes by emphasizing the need for clinicians to be aware of the physical changes that occur during puberty in young athletes.
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Mark Riederer, MD
Keywords
puberty
physical changes
boys
girls
hormones
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