Toe Spring (William A. Rossi, D.P.M.)
If you rest a shoe, new or old, on a table and view it in profile from the side, it reveals an up-tilt of the toe tip varying from five-eighths to one inch or more. More on worn shoes. This is known as "toe spring" and is built into the last.
On the bare, natural foot the digits rest flat, their tips grasping the ground as an assist in step propulsion. Inside the shoe, the digits are lifted slantwise off the ground, unable to fulfill their natural ground-grasping function.
So why is toe spring built into the last and shoe? To compensate for lack or absence of shoe flexibility at the ball. The toe spring creates a rocker effect on the shoe sole so that the shoe, instead of full flexing as it should, forces the foot to "roll" forward like the curved bottom of a rocking chair. The thicker the sole, such as on sneakers or work boots, or the stiffer the sole (such as on men's Goodyear welt wingtip brogues), the greater the toe spring needed because of lack of shoe flexibility.
With toe spring, the toes of the foot are constantly angled upward five to twenty degrees, depending upon the amount of shoe toe spring. Functionally, they are "forced out of business," denied much or all of their natural ground-grasping action and exercise so essential to exercising of the whole foot because 18 of the foot's 19 tendons are attached to the toes.
The combination of the up-tilted toes caused by the toe spring, and the down-slanted heel and foot caused by the heel wedge angle, create an angle apex at the ball where the two angles converge. The angle apex has a dagger-point effect on the ball. This is certainly an important contributing cause of metatarsal stress symptoms and lesions.
But equally important, the natural gait mechanics are affected. Because the hallux and other digits are largely immobilized by their uptilted position, the step propulsion must come almost wholly from the metatarsal heads. This not only imposes undue stress on the heads, but forces an unnatural alteration of the gait pattern itself.
For more from Mr. Rossi: http://www.unshod.org/pfbc/pfrossi2.htm.