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How do growth patterns change from infancy through adulthood?

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Fetal growth — human development Growth of the human fetus from the fourth month to the ninth month of pregnancy.

Human growth is a complex, non-uniform process characterized by shifting rates and changes in body composition from infancy through adulthood.12

Growth Velocity and Phases

In general, the velocity of growth decreases from birth onward. Following birth, the rate of growth in height declines rapidly until about age four or five, after which the deceleration becomes more gradual. This pattern is interrupted by the adolescent growth spurt, during which growth velocity approximately doubles for a period. This spurt typically occurs between ages 13 and 15 in boys and earlier in girls, driven by hormones such as testosterone and estrogen.134

Changes in Body Composition

Growth involves more than just an increase in size; it includes significant changes in shape and tissue distribution. For example, the head accounts for about one-quarter of an infant's total length but only one-seventh of an adult's. Additionally, early development is dominated by cell division, whereas later growth primarily involves the enlargement of existing cells through the accumulation of protein and other materials. Muscle mass also increases significantly relative to total body mass as a child matures into a young adult.21