Why Shock Absorption In Running Is NOT About The Shoes

If you type “shock absorption in running” into Google nearly EVERY hit on the first page is about running shoes. 

Now, this might seem like no surprise or you might even expect this result to occur.  We have been taught, through effective marketing by shoe companies, that cushioned running shoes control impact forces.  The rise of Hoka shoes are a testament to the idea that shoes are the best way to improve shock absorption.

I mean, if the first page of Google tells us that information about shoes will best answer our questions about shock absorption in running, why pursue the topic any further.

In fact, as a consumer, a simple fix like buying a new pair of cushioned shoes sounds like the perfect answer to painful running.  There is little effort needed for a potential large reward. 

If we are being honest with our rational selves (not something we as humans do often unfortunately), we would recall, from many life experiences, that nothing easy and “too good to be true” ever pans out.

So, if shoes aren’t the answer to improving shock absorption in running, than what is? Shock absorption explained You might be asking yourself at this point, “What is shock absorption anyway, and why do I need it for running?”

Shock absorption refers to the process by which a mechanical or hydraulic device absorbs or dampens impact forces.  In running, significant impact forces, 2.5-5x body weight, are acting on the body.  This impact occurs during the initial contact and stance phase of gait.  Basically, the moment the foot touches the ground, and the moment the knee is at peak bend.

Take a look at this slow motion video and you will be able to pick out these running phases.  Also notice that initial contact occurs directly after the “float” phase where both feet are no longer in contact with the ground.
Landing from the “float” phase of running is like landing from a small jump.  In both cases shock absorption is needed to protect the joints of the body.

So, if most of the impact during running occurs at initial ground contact and peak knee bend, then there must be something about these positions that, when altered, can change impact loads. Why Shoes Aren’t The Answer
Everyone knows that you should change your running shoes every 300-500 miles. 

This “fact” has also been driven into our heads over the years.  It makes sense that shoe cushioning breaks down over many miles necessitating newer foam for proper shock absorption.

Although it made complete sense, researchers of course decided to test that theory.  Using a mechanical loading machine that simulates running, shoes were tested to determine the rate at which breakdown occurred in the sole.

Cook et al. discovered that after just 50 miles of running the cushioning in shoes dropped 25%.  After 150 miles the cushioning dropped 33% and after 500 miles the cushioning dropped 45%.

So, by 150 miles, the ability for your running shoes to absorb impact forces was already diminished by 1/3. 

If the shock absorbing capacity of running shoes deteriorates that quickly then something else needs to take the job over or have doing the job in the first place.  

Imagine riding a mountain bike that has both hydraulic shocks and proper "cushioned" tires.  As you start feeling more pressure and impacts with riding is your first thought to change your tires?  Most likely, you are going to check your hydraulics FIRST since you know this has the LARGEST effect on shock control.

If you are looking to control shock absorption in running you need to check your body's "hydraulics".
Why Biomechanics ARE The Answer
Your body's "hydraulics" are controlled by joint angles and muscle function in the spine and lower legs.

A great example is to think of your legs as "springs" that compress and store energy during loading and release energy during propulsion.  In order for this mechanism to work correctly you need to have enough flex or bend at your hips, knees, and ankles.

Take a look at two examples demonstrating poor and proper absorption. 

Poor Shock Absorption, High Impact Forces 

Good Shock Absorption, Low Impact Force

As you can see from the first example, a straight knee, highly flexed ankle, and upright spine increases shock.  From the second example, you see how a proper bend at the lower extremity joints dampens shock.

To be able to use your legs like "springs" you need strong muscles at your core, hips, quads, and calves.  These muscles need to control motion in multiple directions and keep your legs in proper alignment to keep forces to a minimum.

Great shoes can't compensate for poor mechanics.  Great shoes can assist the body in shock absorption...at least for the first 50 miles.

So next time you are looking to make your running less jarring, I wouldn't rely on Google's first page suggestions.

Train the "machine" first.  Great running is NOT about the shoes.

For more information on improving your running form to decrease injury and enhance performance, check out the helpful information here.

Written by: Kevin Vandi  DPT, OCS, CSCS

Physical Therapist serving San Jose, Los Gatos, Campbell, Almaden