Heal to toe running is a thing of the past and somewhat archaic. The human foot is designed to absorb impact through the arch, which is a natural shock absorber. By landing mid to forefoot (depending on how fast you are going) the tendons and natural shape of the foot absorb the impact like a spring. When you land on your heal the shock is sent right up through your leg into your knees, hips and back. Shoes are typically overbuilt in the heel region but there is a move to create shoes with less of a prominent heel as we move towards a more mid to forefoot landing surface.