Running shoe serves to enhance athlete’s performance by providing cushion for the massive amount of vertical impact that a feet and knee sustain during the course of running. Although most people understand the utility of the running shoe in cushioning against impact through the presence of the foam layer, relatively little is known, to the public, about the entire structure of a running shoe, and, more importantly, how its construction helps facilitate the reduction of shock, while enabling an efficient transfer of energy from the foot to the ground in aid of fast running.
Viewed from the side, a running shoe comprises three main layers: upper mesh, midsole and outsole. The upper mesh is usually decorated with different colors and design, and its primary function is to allow efficient heat and air exchange between the foot and surrounding air for runners’ comfort. More importantly, design of the upper mesh also serves to lock the foot in place during running, which in reducing the amount of sliding in the shoe, enables more efficient energy transfer to the ground; thereby, providing greater energy input for the forefoot liftoff.
The main cushioning effect from running shoe comes from the foam layer, which is encapsulated in the midsole. Different types of foam are used for differing load conditions; for example, a running shoe designed for jogging would have smaller amount and lower quality foam compared to one tailored for fast running. Shock absorbing properties of the foam layer derives from the elasticity of the foam material in absorbing shock (resulting in depression of the foam layer) and subsequent “rebound” after removal of vertical load during a running step. Although only a single type of foam is used in most cases, different foam material could be used in high performance running shoes to achieve better cushioning effect in the heel and toe area of the shoe, the respective sites for landing and liftoff during running.
Finally, the layer of the shoe that directly contacts the ground for achieving grip and traction is known as the outsole. Besides preventing sliding, the outsole design and thread pattern is also crucial for energy transfer to the ground, as well as reducing propagation of shock waves during ground impact to the feet and through to the knee. Specifically, thread pattern comprising of small and thin extrusion from the main sole material usually lead to smaller pressure on the feet and transfer of shock waves to the knee. On the other hand, thread pattern with elevated outcrops of contact patch with the ground tend to increase pressure exerted on the foot and knee during running due to the reduced surface area in contact with the ground. In choosing an outsole design, attention should also be placed on the durability of the material, especially if you are running on high abrasive surfaces such as concrete.
Collectively, running shoe design is an art form that traverses the challenge gauntlet from enhancing the visual impact of the upper mesh while retaining its functional utility in allowing a breathable run, to creating a smooth and comfortable running experience without pain through allowing for appropriate amount of suitable foam material in the midsole, and finally, delivering enough grip in an outsole design that also would not cause elevated pressure and stress on the knee and foot during impact. Combining the three design elements require the thoughtful consideration of the shoe designer and outsole design team in selecting the appropriate material and crafting them in a shape and pattern that reduce the load and stress on the knee, which gives the runner the confidence to train further and run faster. While advanced sport science and engineering could facilitate the design and construction of better running shoes than what is available commercially, the corresponding elevated cost would put the shoe out of reach to the average runner; thus, running shoe design remains an art form, where major brands in the trade employ the expert opinion of professional and world beating athletes for their input on what makes a running shoe unique in performance in different running conditions and styles ranging from minimalists to a weekend sport enthusiast and an average runner.
Category: sport science, materials,
Tags: foam layer, shock absorption, impact cushioning, midsole, outsole, thread pattern, running shoe, grip, traction, mesh,
Acknowledgement: Ng Wenfa thank Seah Kwi Shan for co-authoring this blog post.