Let’s talk about the midsole

This column is called Oddities but today we might as well call it Wikishoes, because more than a curiosity (which, also, it is) today’s topic is a notion, a knowledge concerning running shoes. Today we talk about the midsole.

What it is not

Let’s start by first saying what the midsole is not. The name is very often misleading, but let’s make it clear: the midsole is not the sole, although it is integral to it. The sole is in fact the part of the shoe in direct contact with the surface on which the foot rests and serves to isolate the foot contained in the upper from the ground. The term tread sometimes replaces that of sole, but it really only indicates the surface in direct contact with the ground and not the entire thickness of the sole. The misunderstanding stems from the fact that the sole is a part of the traditional smooth, unsculptured shoe. Instead, the tread (just like that of car tires) is more or less sculpted, depending on the use for which the shoe is intended, from smoother for road shoes to more sculpted for trail shoes (to mountain boots). The heel is not part of the sole but is an element added later in both men’s and women’s soles. That’s another clue that the sole is not the tread-even if the two terms are now interchangeable or tolerated. Since in the running shoe the heel is integrated, it is obviously unnecessary to make this distinction, so the sole includes it.

Okay, but what about the midsole then?

The midsole is everything between the sole and the upper, i.e., the material that cushions and cooperates mechanically with running.
The introduction of the midsole is relatively recent and does not date back many decades. It is believed that the first shoe to use a foam between sole and upper to ease and “soften” the ride was the Nike Cortez in 1972. The purpose was to facilitate the practice of running-at the time called jogging and understood as alternating walking and running-while avoiding injuries that were almost mathematical with traditional shoes without cushioning.

Nike Cortez 2015, l’Atto della Fondazione

From today’s view of the midsoles, this was a shoe that, because of the lack of cushioning, we today would call a sneaker and certainly not a running shoe. It was a start, though, certainly one that gave the impetus for others to produce different versions and to develop ever new solutions.

The midsole today

Today the midsole has evolved so much that the cushioning function is only one of the things it does. Certainly its vocation remains to make running more comfortable and to minimize the force of foot impact on the ground, even considering that the weight of a runner becomes 2-3 times that borne during a walk.

We can distinguish its two main functions into: passive and active. The passive function is the same as the Nike Cortez of five decades ago, which is to dampen the impact and transmit less force to the ankles and legs in order to preserve the joints.

The active one, on the other hand, is delegated to its ability to return stored energy during landing, to add a component of force and propulsion in the detachment from the ground. Exactly: the midsole also has the function of a spring (or a mat of springs, if you prefer) that you load when you land and that unloads back by giving you a little more help to move forward when you take your foot off the ground.

This effect had to wait until materials with similar mechanical properties were invented. It did not have to wait long: as early as 1975 Brooks used EVA for the first time (ethylene vinyl acetate, also known-get ready for the cuddliest name in the running world-“Mattress”) in its Villanova model. From that day on, all major manufacturers introduced this new midsole in their shoes, and it is still one of the main solutions today.

But it is not the only one (toward the new frontiers of midsoles)

The running shoe, in the end, is made of very few things: an upper, a midsole, and a sole. End.

Seeking to evolve to improve performance and offer increasingly efficient tools for runners, brands have focused almost exclusively on the one component that can percentage-wise contribute the most: the midsole. In fact, going by exclusion: the upper can weigh as little as possible, the sole can give you the best grip in the world but only the midsole can make the real difference. Which is in fact the one that has evolved the most in the last 10 years.

The first evolutionary leap involved the very foam with which it is made: it was 2013 and Energy Boost, a new elastic material that performs better than EVA and can return more energy, developed by adidas with BASF, was born.

In subsequent years, almost all brands have complemented their EVA collections with some lines featuring proprietary foams in different materials that had and have the function of maximizing energy returns and reducing weight as much as possible. Here come new names and acronyms such as TPU, Ignite (PUMA), Freash Foam (New Balance), Zoom X (Nike), Nitro (PUMA again), Lightstrike (also adidas) and others.

The story is not over yet, although it is best to end it here for today. I will leave you, however, with the last real revolution of this last five years: the use of carbon. That, not surprisingly, involved the midsole once again.

Present in various configurations and according to different brands’ recipes, carbon appears in carbon plate form or infused in rod form (adidas’ Energy Rods ) with the function of maximizing energy return. In other words, it is as if the elastic and mechanical qualities of midsole foams are amplified by a material that has even more extreme mechanical performance and is housed (in the form of one or more plates or bars) within them.

To go stronger and stronger, also because of it. And let’s not call it a sole anymore, it will be disapponted.

(Main image credits: Amvorsup on DepositPhotos.com)


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