The importance of the sole, midsole and fasteners on trail running shoes

As we discussed on our previous article, fasteners are extremely important. A key technique while trail running is to use the seventh buttonhole of our shoe if available. We normally don’t and sometimes we are not even aware of its usefulness. 1The mission of this seventh buttonhole is to provide an additional fastening capability to our shoe. By securing it to our ankle, we limit its range of forward movement. And this is specially important in the downhills since it is when we may impact against the front of the shoe, causing bruises under our fingernails. Likewise, by restraining the movement of our foot we can also reduce the skin friction and hence prevent the formation of blisters.

On the other hand, zip-up shoelaces have become popular lately among trail running footwear brands. If our shoe has them we need to store them in the small pouch available in the tongue. Doing so will prevent it from becoming entangled with branches or protrusions, causing us to fall.


By midsole we mean the part located between the sole and the top. For many this is the key component of the trail running shoe.

It needs to serve a number of functions, like padding the foot and controlling its abnormal or excessive movements (pronation or supination). The first materials to be used for this were Ethylane Vynil Acetate (EVA) and polyurethane (PU). EVA is a light foam with an optimal padding capacity, but it wears down easily. The solution is to use compression molded EVA, which makes it stronger and more durable. On the other hand polyurethane is more resistant but also offers less padding.

Nowadays most sports footwear are made out of gel, foam or some other materials, all of them brand-specific. This type of padding makes the midsole more durable while improving its stability and shock absorption. Generally speaking, this the aspect which highlights the majority of differences in quality between the different shoemakers. And it is also the key to the “tech warfare” they are waging with each other. Apart from that, thermoplastics have also been added to control the central torsion movement of the foot. We can very easily recognize them in the rigid estructures occupying the centre of the sole. 1

  • A shoe with “antipronation” midsole (used by pronation-prone runners) will have a denser and firmer foam in the internal side of the midsole, usually highlighted with a darker shade of color. We can check it by feeling that area and comparing it with the rest of the sole, as it is common for trail running shoes to use a dark color for its entire length. 1
  • If the shoe has an “antisupination” midsole that denser foam will be on the outer area, although this type of footwear is not normally found on average stores.
  • A midsole will be neutral if it does not have any of these internal or external reinforcements. If in doubt about the type of midsole of a given model, one should ask around in specialized stores.

To know our type of gait and hence to choose the optimal shoe for us we strongly recommend to visit the podiatrist and to ask for a comprehensive footstep study, dynamic as well as static, and even better if it includes running tests. If we choose to use insoles we need to use a neutral model, as the needed correction is already incorporated into the insole itself.


The running shoe sole is a fundamental part of our choice. There are several possibilities when it comes to the designs, the rubber-based materials and the length of the heels. In trail running the most common type of rubber used is low density (soft), to allow for a better grip on rocky or grassy terrains. That’s the main reason to avoid the use of trail running shoes when running in asphalt, as the sole will quickly wear off. The design will be pronounced and the heels long as we require better grip and traction than over asphalt.1It is essential that the sole runs all the way to the tip of the shoe or at least that is has some sort of reinforcement there, protecting our fingers from impact. With these simple tips we are confident that you’ll be able to make a better and more informed choice when buying a trail running shoe. 


Javier Salinero Martín
Transvulcania Podiatry Service


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