7.1: Size and Proportions

Body growth is not a smooth or gradual process. In fact, the child grows in many spurts and starts. As mentioned in the section about newborns, the average newborn in the United States weighs about 7.5 pounds and is about 20 inches in length. After about a 5% weight loss in the first few days, there is a period of rapid growth. By the time an infant is 4 months old, it usually doubles in weight and by one year has tripled its birth weight. By age 2, the weight has quadrupled. The average length at one year is about 26-32 inches.[1]

Two hormones are very important to this growth process. The first is Human Growth Hormone (HGH) which influences all growth except that in the Central Nervous System (CNS). The hormone influencing growth in the CNS is called Thyroid Stimulating Hormone. Together these hormones influence the growth in early childhood.

Proportions of the Body

One dramatic physical change that takes place in the first several years of life is the change in body proportions. The head initially makes up about 50 percent of our entire length when we are developing in the womb. At birth, the head makes up about 25 percent of our length (think about how much of your length would be head if the proportions were still the same!). By age 25 it comprises about 20 percent our length. Imagine now how difficult it must be to raise one’s head during the first year of life! And indeed, if you have ever seen a 2 to 4 month old infant lying on the stomach trying to raise the head, you know how much of a challenge this is. The comparison in this graphic was originally introduced in the last chapter.

Figure \(\PageIndex{1}\): Shown from left to right: Human body proportions at birth, at 2 years, at 6 years, at 12 years, and at 19 yearsHuman body proportions changing as the subject matures. The diagram shows that the head becomes proportionately smaller and the limbs become proportionately longer as the subject matures..[2]

Some of the most dramatic physical change that occurs during this period is in the brain. At birth, the brain is about 25 percent its adult weight and this is not true for any other part of the body. By age 2, it is at 75 percent its adult weight, at 95 percent by age 6 and at 100 percent by age 7 years.

Growth in early childhood

Children between the ages of 2 and 6 years tend to grow about 3 inches in height each year and gain about 4 to 5 pounds in weight each year. The 3 year old is very similar to a toddler with a large head, large stomach, short arms and legs. But by the time the child reaches age 6, the torso has lengthened and body proportions have become more like those of adults. The average 6 year old weighs approximately 46 pounds and is about 46 inches in height. This growth rate is slower than that of infancy.

During the early childhood years of three to five we see significant changes in the way children look, think, communicate, regulate their emotions, and interact with others.

Figure \(\PageIndex{2}\): Two early childhood kids - a girl and a boy - contrasted in size.[3]

Middle childhood

Figure \(\PageIndex{3}\): Stature for age and weight for age percentiles of boys – these are charts used by pediatrician offices to graph children’s weight over time.[5]

Figure \(\PageIndex{4}\): Stature for age and weight for age percentiles of girls – these are charts used by pediatrician offices to graph children’s weight over time.[5]

Physical Growth in Adolesence

The adolescent growth spurt is a rapid increase in an individual’s height and weight during puberty resulting from the simultaneous release of growth hormones, thyroid hormones, and androgens. Males experience their growth spurt about two years later than females. The accelerated growth in various body parts happens at different times, but for all adolescents it has a fairly regular sequence. The first places to grow are the extremities (head, hands, and feet), followed by the arms and legs, and later the torso and shoulders. This non-uniform growth is one reason why an adolescent body may seem out of proportion. During puberty, bones become harder and more brittle.

References

Polan EU, Taylor DR. Journey Across the LifeSpan: Human Development and Health Promotion. Philadelphia: F. A. Davis Company; 2003, 150–51

Attributions:

Child Growth and Development by Jennifer Paris, Antoinette Ricardo, and Dawn Rymond, 2019, is licensed under CC BY 4.0

[1] Lifespan Development - Module 4: Infancy by Lumen Learning references Psyc 200 Lifespan Psychology by Laura Overstreet, licensed under CC BY 4.0

[2] Image by Ephert is licensed under CC BY-SA 4.0

[3] Image by Kevin Gent on Unsplash

[5] Images by the CDC is in the public domain