From the Bones for Life® website
A dynamic and springy walking style is the natural motivation which stimulates the organism to strengthen its bones. It is the rhythmical pulsations of lively steps that enable the blood, which carries nutrients and oxygen, to penetrate the solid tissue of the bones and provide for growth of new bone cells. A well-aligned posture and harmonious coordination of movement are essential for sustaining the springy pressure of this dynamic walk which can stimulate bone strength.
Comparative research shows that African women, who carry massive loads on their heads with effortless grace, are one hundred times less liable to fractures than women in the West, despite the fact that their bone density is lower than that of Western women.