The resistance (R) of any curved column to compression forces is directly proportional to the square of the number of curves (N) plus one (R = N
2 + 1). Therefore, the fetal spine with its single curve has a resistance value of 2 (12 + 1 = 2). This is not enough to resist the forces of gravity against the head, neck, and upper trunk as we saw in Figure 1. The development of the cervical curve increases the resistance value of the spine by 2.5 times (22 + 1 = 5).