Part 1: Adolescent growth and development

Authors:
Aditya Mahajan, Aman Bindra
Assessment Division,
Institute of Nutrition and Fitness Sciences (INFS)

Synopsis:
Participation in sports plays a crucial role in child’s development and well-being. Many young athletes have been able to achieve outstanding sports performance. Swimmer Michael Phelps, for example, competed in Sydney Olympics when he was only 15. Arnold Schwarzenegger started training when he was 15 and won his first Mr. Olympia title when he was 20. Young athletes are, therefore, a special population which require special focus.
From early childhood to maturation, children undergo number of physical, hormonal and cognitive changes each having a direct relevance to the training and nutrition demands. Hence, it is important to gain understanding of these changes in order to enable the child to perform at it’s full potential. In this first article of INFS Health series, following topics were covered:
➢ Changes in body composition: Height, Body fat, Fat-free mass, Bone-mineral density
➢ Changes in strength
➢ Changes in hormonal profile
It’s a known fact that the young athletes possess a greater risk for abnormal growth and susceptibility to serious injuries. Therefore, in this article, we discussed why it’s inappropriate to consider adolescents as the “young adults”.

Keywords: Adolescent, Athlete, Nutrition, Strength, Maturation

Introduction:
As per a study, 75% of the teenagers drop out of sports by the age of 15. The major factor responsible for this is that their coaches make them perform beyond their development capabilities leading to increased risk and chances of injuries, disappointment, and discouragement. This leads to giving up of the sport altogether. Hence, it is really important to have a thorough understanding of the physical and cognitive growth and development of a child in order to create any successful sports program.
There are many factors which need to be considered while developing the guidelines for a young player or an athlete. In this article, we will discuss these physiological and hormonal changes in detail to lay the foundation of demands of the young athletes. If you are a coach to a young athlete or a parent who wish to support their child’s athletic endeavor, understanding their level of development will help you to establish a positive and an effective relationship with the athlete and will ensure that you support them in the most beneficial way.

1. Changes in body composition:
A) Height:
During adolescence, it has been observed that majority of the growth in height is achieved during a single growth period or “growth spurt”. It is estimated that 15-25% of final adult height is gained during this growth spurt. Generally, the period of the spurt lies between 12 to 15 years for females and 14 to 17 years for males.

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Peak height velocity (PHV) is defined as the period of the maximum rate of growth, i.e the time when a child grows fastest during the growth spurt. It is considered as the major determiner of the frequency, intensity, and duration of the strength and aerobic exercises by the coaches. The PHV is typically attained around the age of 12 years for girls and14 years for boys.

B) Body fat:
Total body fat (in Kgs) increases with age. However, the rate of gain is greater in females than males, particularly at a young age. By the end of the puberty, average adolescent girl acquires around 26-31% of body fat. Females generally continue to gain body fat percentage with the age but the velocity of gain declines annually and reach a minimum at an age of 15Y and then start increasing thereafter.
Boys experience an increase in body fat percentages from age 8-12 years and then a significant decrease until 18 years of age. This is largely contributed to the greater production of testosterone.

C) Fat-free mass (FFM):

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Source: Vaughn I. Rickert, ed. Adolescent nutrition: Assessment and management. Jones & Bartlett Learning, 1996.

The fat-free mass increases almost linearly with age till the puberty. Before puberty, both males and females have a comparable amount of Fat-free mass (FFM) but males generally have substantially greater FFM thereafter. This is primarily due to the fact that both males and females have similar hormonal levels before hitting the puberty but post-puberty, the difference in hormone sky-rockets.
During the age group of 10-20 years, average male gains approximately twice the FFM than an average female.

D)Bone mineral density (BMD):
BMD increases progressively with age from birth to early adulthood. The mechanism is basically dependent on centrally regulated hormonal factors and mechanical factors. However, adolescence is one of the most critical phases of the overall bone development. The cross-sectional data suggests that a short period of the pubertal year adds 5-70% of the total bone mass. It has been reported that girls reach PBMD (Peak bone mineral density) between 16-23 Years of age and boys, between 16-25 years.
Bone mass adapts to the mechanical strain placed on it by skeletal loading. Changes in bone mass are localized to the induced strain and there may be a net bone increase or net loss occurring simultaneously in different parts of the skeleton. Interestingly, the intensity of the forces that act upon the body, and not the duration of the exercises, is a key factor affecting the bone health. The high magnitude and high rate intermittent loading have shown to produce the significant osteogenic effect. Therefore, short bursts of explosive exercise are effective for bone development as well as muscle mass.

Figure: Changes in bone mineral density with age

2. Changes in strength:
It is known that maximal muscle force production is significantly lower in children than adults, even when different factors such as body mass and muscle cross-sectional area is normalized. Data from several studies suggest that age and weight are the prime predictors of strength between 3.5 and 15 years of age. The strength increases progressively in an almost linear manner from early childhood and throughout the adolescence, the major contributing factors being a gradual increase in the body size (height, weight etc.) and body composition (muscle mass, bone mineral density etc.) with age. This is followed by a somewhat slower increase in the early or late 20’s. However, their lies gender-based differences. Boys seem to experience a greater increase in the arm isometric strength than girls but the increase in lower limb isokinetic strength is somewhat similar between both sexes. Also, this rate of strength gain is sex-dependent. The rapid increase in strength during puberty in males has been observed after which the rate of increase slows down. On the other hand, the rate of increase in strength in females is almost constant between pre-pubertal and post-pubertal phases. These gender-based differences can be explained by the difference in the changes in body composition with age. While the subcutaneous fat increases in girls, the boys experience a relative increase in muscle mass with age (as explained above).

3. Change in Hormonal Profile:
There are a dozen hormones of importance in the control of human development. A transition between childhood and adulthood is a very crucial stage. This is the stage of significant changes, which leads to puberty. During puberty, dramatic changes occur in the hormonal profile, and especially in the hypothalamic-pituitary-gonad (HPG) axis. The gonads secrete hormones in sufficient amount which results in the accelerated growth of the genital organs and the conspicuous appearance of secondary sexual characters. The most obvious changes are brought about by the increase in the secretory activity of gonad and interaction with adrenal sexual hormones. The peripheral increase of Testosterone and Estrogen along with their characteristic events follows.
Girls pass through various stages of puberty at an earlier age than boys do (generally 18–24 months earlier), with girls beginning at the approximate age of 8 and boys at 9. For males, rapid annual increase in the testosterone levels are observed until the age of 14 after which it hits a plateau. For the female, the increment is not that linear. T-levels shows little change in the 9- year-olds across the span of 1 year followed by a slight rise in the 10- and 11-year-olds and the changes in T become more variable in the 12-, 13-, and 14-year-olds because of menstrual cycle variations.
It’s important to understand that each child is unique and therefore, they grow and mature at a different rate. For example, in a 1943 study, Schoenfeld et. al observed that 4% of 10-year-old boys already showed pubescent signs, but 6% of 14-year-old boys showed none yet. And a similar study in girls by Can’t Land & De Hass et. al showed that, whereas 12% of 12-year-old girls had started to menstruate, another 12% of 15-year-old ones had still to experience menarche, with a range of 11–16.3 years of age. These individual differences in hormonal levels at the same chronological age pose important theoretical and methodological considerations. Genetic factors and timing of puberty, as well as other environmental (climate, light, temperature, etc.), socioeconomic (nutrition, urban vs. rural, stress, etc.) and experiential factors (experiences of success and failure), contribute to these individual differences in hormone levels at puberty.
Also, there is some evidence that suggests that higher body fat percentage during childhood may influence the onset of puberty as well. The higher body fat percentage delays puberty in boys and advances puberty in girls.

Conclusion:
In conclusion, from early childhood to maturation, people go through several stages of development resulting in a number of changes in the body composition, hormone levels, and strength. The succession of these events during puberty is consistent among adolescents, however, this degree of maturation (physical and biological) is not universal and there may be a great deal of deviation in the age of onset, duration, and tempo of these events. For this reason, adolescents of the same chronological age can vary greatly in physical appearance and strength. You, as a coach or a parent, must understand these differences since this has a direct relevance to the nutritional requirements and training programs of a child.

 

References:
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12. Schoenfeld, W. A. (1943). Primary and secondary sexual characteristics: Study of their development in males from birth through maturity, with the biometric study of penis and testis. American Journal of Diseases of Children, 65, 535 – 549.
13. can’t Land, G. M., & de Hass, J. H. (1957). Menarche-leeftijd in Nederland. Nederlandse Tijdschrift voor Geneeskunde, 101, 1425 – 1431.
14. Andreu, J. M., & Ramirez, J. M. (in press). Biological, social, and contextual dimensions of human aggression. A new tridimensional construct. International Review of Social Psychology
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