last measurement of how high the toe point stands above the ground plane
Many shoe lasts have at least some toe spring, for various reasons:
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Pre-bending the ball reduces stress on the forefoot when the ball of the foot bends, especially from shoes with thick or reinforced soles.
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Pre-bending the vamp reduces creasing that may show as rolls or deep wrinkles on the most visible part of the shoe.
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Wearers are accustomed to how slightly sprung toes look and feel.
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Springing the toe may reduce tripping outdoors.
Overall, lasts with higher heel height tend to have less toe spring. Shoes with particularly thick or inflexibles soles tend to have more toe spring.
Some rock climbing shoes have negative toe spring to aid toe holds on small protrusions. Similarly, the toes of pointe shoe lasts point down.