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Running shoe construction – The Midsole

Potentially – the most influential part of your running experience.  Often overlooked, under valued or misunderstood altogether.

Here are the facts.

  1. Feet can’t tell midsole from floor.
  2. The body’s ability to maintain good running form will be influenced by the characteristics of a midsole.
  3. The midsole dictates the life of your shoe.
  4. Midsoles can only make you faster, or go further if you’re prepared to do the work.

How does all this affect you and your running?


If you’re moving well and your midsole is too deep (for you) it will cause you to lag when applying pressure (mid-stance).  If you heel strike or over-stride, it can cause instability upon contact with the ground and throw your foot the wrong way, which can be damaging, or simply more demanding when trying to reach the correct position to push strongly through the big toe.


The same can happen when midsoles are too flexible or unstable (often due to channels being formed in the underside to allow too much movement or reduce weight.

Added plastic, inserted for ‘stability’ often causes a permanent and unavoidable obstruction for the foot when transitioning between landing and take off.  ‘Support’ or ‘Motion Control’ shoes have been found to train runners’ to the point where they’ve learned t do the best of a bad job, rather than generating sufficient strength in order to perform the correct movement for the desired length of time.

Busting a gut in a deep cushion midsole will undoubtedly involve wasted energy.  You want to push and move, but that depth of cushion means sinking into your shoe when you wish to propel yourself.


Too minimal a midsole and there’s a much better push-off when moving well.  But as soon as you fatigue, the form starts to go.  Lack of good form in a minimal shoe (or off-road shoe on tarmac), results in a lot of trauma.  Impact that cannot be absorbed by the body and isn’t therefore dampened by the shoe either, ends up hammering joints, soft tissue, or both.  Ouch.

Flexibility gone mad:

Sufficient depth, without the correct structure can be a very difficult to work with, despite feeling supremely comfortable when first put on your feet.  A lot of modern footwear is designed to act like a pack of uncooked jelly, with segments of gooey material left to flex in all directions for a complete freedom of movement.  the problem for some is that their foot never stay still and won’t allow any consistently controlled movement while under extreme load or again, once tired.  ‘These feel like slippers’ is an over used response in-store.  Would you go for a run in your slippers……?

Life expectancy vs expectations:

Midsoles are designed to resist Impact, absorb shock and take you hundreds of miles before giving up the ghost.  But they all wear out eventually.  Whether filled with tiny air bubbles or moulded from the latest e-tpu rubber for extra wear and extreme return, at a molecular level after all that impact, it dies.  Most current high mileage training shoes will be designed for an intended 500miles of running.  Not walking.  Not gym sessions, cross-fi, or hiking.  Road shoes are not designed for trails or open country and visa-versa where Fell or Trail shoes are concerned.  Despite the fact that we all use a shoe for more than its intended purpose on occasion, you can’t expect it to stay in one piece forever.

If a shoe does go for its respective mileage allowance, while remaining in one piece, with plenty of tread left – it’s still dead under foot.  That midsole will have lost enough structure to allow it to fail.

When air is trapped in rubber, it will compress under load.  The air will re-expand once the load is removed (foot leaves the ground).  Repeat this for 500miles and the rubber is breaking down, just like a metal bar when bent back and forth, over and over.  The ability for that midsole to resist impact and reform is all but gone, which is why you feel every lump of gravel through the shoe all of a sudden.

It therefore cannot be taken as a good sign that your tread is still intact, or that no holes have appeared in the upper, when the simple fact is – at the appropriate mileage, the shoe is no longer healthy.

Finally: – no midsole can make you faster.  You do the work.  The shoe protects your foot while you work.  It can feel comfortable.  It can bounce back to full form in record time.  But it won’t propel you automatically.  You’ll still have to push.  You’ll still have to control the position of your foot during landing, mid-stance and take off – when tired.

Note: When attempting to maintain good form, it is important to understand the body’s needs.  It takes approximately 6 weeks for any influence to affect permanent change on the body.  Anything less than 6 weeks and your body will react to the influence as if it were a temporary setback.  Gradual introduction of workload (including a new style of footwear) will allow you to condition the body, while avoiding fatigue or injury through overworking.  This leads to improved strength and fitness without immediate fatigue or injury through overload.


To recognise the needs of the individual and understand the appropriate options in order to try one midsole against another until a favourite can be selected from those which appear successful, that’s where Accelerate come in.

That’s why we have a range as broad as we do.  And the staff team of regular runners, who know the value and the purpose of the shoes we stock.

We carefully match the runner with the product for a more positive running experience.

Learn more about running shoes below


Grip VS Traction

Outsoles >> Grip VS Traction >>

Accelerate UK: The area's largest Running Store for road, trails, mountain and fell. From parkrun's through to ultra marathons. A wide range of shoes and running items that is backed up by a knowledgeable and experienced running staff. At Accelerate we love our running, and we believe it shoe. Come and say Hi, "The kettle is on"