The cervical and lumbar curves are compensatory or secondary curvatures, and are developed after birth, the former when the child is able to hold up its head (at three or four months), and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to walk.

At what age do the secondary curvatures typically become established?

The secondary curve of the lumbar region starts to form between the fifth and the thirteenth month of an infant's life. This curve, which is responsible for the arch of the lower back, is not fully developed until a child reaches 8 to 10 years old.

Under what circumstances do secondary curvatures develop?

A secondary curve develops gradually after birth as the child learns to sit upright, stand, and walk. Secondary curves are concave posteriorly, opposite in direction to the original fetal curvature. The cervical curve of the neck region develops as the infant begins to hold their head upright when sitting.