The design principle and importance of shoes and shoes

The shoe last is a fundamental element in the design of labor safety shoes. It serves as a mold or support that determines the shape, fit, and protective function of the footwear. The design of the shoe last must be based on the natural shape of the foot, but it cannot be an exact replica because the foot changes in size and pressure during movement and under different conditions. Additionally, factors such as material properties, shoe style, and environmental use all influence the final dimensions of the shoe. As a result, modern labor safety shoe design involves multiple disciplines and requires both technical expertise and practical experience.

Design Principles for Labor Safety Shoes

The length of the foot is the primary reference when determining the size of the shoe last. However, the length of the shoe last must always be slightly longer than the actual foot length. This is due to several reasons:

First, the foot can expand or contract depending on weather and physical activity. For example, temperature changes may cause the foot to swell by up to 3–5 mm, and prolonged walking or heavy labor can also increase foot length. Second, there is a necessary "allowance" within the shoe to allow for foot movement. Men's shoes typically have a 20 mm allowance at the toe, while women’s shoes usually have 16.5 mm. The amount of allowance varies depending on the shape of the toe—narrower toes require more space, while wider toes need less. Lastly, the heel of the shoe last should have a slight convexity (called "back tolerance") to accommodate the natural curve of the heel, ensuring better fit and comfort. Typically, this tolerance is about 2% of the heel circumference, with men's shoes having around 5 mm and women’s shoes around 4.5 mm.

For example, if a person has a foot length of 250 mm, the base length of the shoe last would be calculated as: 250 mm (foot length) + 20 mm (allowance) – 5 mm (tolerance) = 265 mm.

Foot Circumference and Length

The circumference of the foot is crucial in determining the fit and comfort of the shoe. While the length provides the base measurement, the circumference helps determine how snug or loose the shoe will be. For instance:

(1) Ankle Circumference

The ankle circumference is a key factor in ensuring the shoe fits comfortably and supports the foot properly. If the circumference is too tight, it can cause discomfort and even damage the surrounding areas over time. The ankle circumference also affects other parts of the shoe. For example:

- In shoes with a pointed toe, the toe circumference should be 3.5 mm smaller than the ankle circumference to ensure proper coverage without pressing against the toes.

- In low-cut shoes or those with a tongue, the ankle circumference should be 7 mm smaller to allow the foot to move freely without restriction.

- In high-top or boot-style shoes, the circumference can be equal to or slightly larger than the ankle, especially for high boots, which may require an additional 3.5 mm for comfort.

(2) Midfoot and Toe Circumference

The midfoot and toe circumference should generally be 1–6 mm larger than the foot itself, depending on the design. However, the relationship between these measurements is not fixed. Different girths can create varying shapes, so it's important to consider how the girth affects the overall structure of the shoe. Therefore, accurate planning of the girth and shape is essential for a well-fitted pair of labor shoes.

Width and Height of the Shoe Last

The width of the shoe last is determined by the width of the foot. There are two main types of foot widths: wide and narrow. However, these measurements are not directly used as the final width of the shoe last. Instead, the width of the last is adjusted based on the shape of the foot and the design of the shoe. For example, the front and rear ends of the shoe last include some extra space for movement, while the middle part is designed to balance the outline and footprint widths.

Additionally, the height of the front and back parts of the shoe last must be carefully coordinated. When the heel is higher, the front of the shoe tends to be lower, and vice versa. Generally, for every 10 mm increase in the heel height for women, the front of the shoe decreases by about 1 mm. Similarly, for men, a 5 mm increase in heel height results in a 1 mm decrease in the front of the shoe.

Base Line of the Shoe Last

The insole base line of the shoe last includes several key measurements relative to the foot length:

- 18% of the foot length at the curved part,

- 41% at the lumbosacral area,

- 63.5% at the fifth toe,

- 72.5% at the first toe,

- 78% at the outer edge of the little toe,

- 90% at the big toe.

China Labor Insurance Network