Shoe Design Parameters
In addition to comfort and fit, key shoe design parameters are flexibility, stability, durability and traction. Let's examine what these terms mean and how the shoe components contribute to these attributes.
Flexibility:
Flexibility refers to the shoe's pliancy - its ability to yield and bend. Depending on the sport, flexibility is built in or minimized in a shoe. For example, a football place-kicker requires a stiff area in the forefoot (the area between the ball of the foot and the toes), while a running shoe deforms with the human foot's natural flex lines. There are tradeoffs. A highly flexible shoe can jeopardize stability and durability. As you can imagine, the cushioning system used in the midsole may compromise flexibility. However, athletic shoe scientists and designers endeavor to meld flexibility into the shoe's midsole and outsole along the foot's natural flex lines.
Durability:
Durability means the shoe's ability to endure and perform over time - to last and continue to maintain its stability, traction, flexibility and shape (fit). Durability is dependent on the materials, structure and construction of the shoe and is managed in each shoe component differently.
For example, the bottom of the outsole wears based on the amount of friction it encounters. Researchers have isolated friction contact points to reduce wear in those areas. Durability of the upper is dependent on the materials used commensurate with the sport and foot motions. A case in point, baseball pitchers may wear the toes of their shoes faster than players in other positions. In the midsole, the materials and construction of the cushioning system govern its durability.
Stability:
The upper and midsole are key to providing
stability to the foot. Stability is the capacity
to resist forces which would cause motion or a change of motion.
"High top" or "three quarter" height uppers may provide additional support
to the ankle to prevent sprained ankles. To add stability,
heel counters have been integrated from the midsole to the upper.
One concern for designers is that cushioning systems may be so
soft that they compromise stability - an important design consideration.
Footwear stability in court sports like tennis and basketball is incredibly important since it is estimated that as many as 45% of all lower extremity injuries occur in the foot and ankle.
Traction:
Traction created by the friction between the outsole and the surface allows the shoe to grip the surface. As surfaces, conditions and player motion change, traction may need to vary. An athletic shoe needs to grip well when running but not when pivoting. For hard court sports you do not want the shoe to grab the surface and stop so suddenly that you turn an ankle.
