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PORON Cushioning Blog

Ground Force Transmission / Reduction in Footwear

Posted by Dave Sherman on Thursday, September 22nd, 2016 | 3 Comments »

By Samantha Brey, EMS Marketing

Out of all the sports, dance classes, and every type of movement under the sun, the second most popular form of exercise in the world is running. Why is that? Many say running is a great stress reliever, it enables them to break fscreen-shot-2016-09-22-at-10-28-53-amree of the daily routine and burn calories at the same time. Running also requires minimal training to master and takes little to no equipment to practice. It can be done alone or with friends whenever is convenient; with limited time constraints. Running combines many of the best aspects of different types of exercise into a sport that can be done casually or professionally by anyone who chooses.

But what are the downsides to running? How does running compare to other forms of exercise when injuries are considered? It is estimated that around half of the running population gets injured every year. But what’s causing these running injuries?

Ground Reaction Force (GRF) is the scientific term for the way the ground pushes back when it is struck. According to Newton’s Third Law, for every action there must be an equal reaction. Ground Reaction Force is a perfectly normal, natural occurrence that can make things difficult, and sometimes painful, for a runner.

When a runner’s foot strikes the ground, the impact and GRF can cause injury to the foot, ankle, and other joints. These injuries are impact-related, but they can often be prevented with some research and calculations. For instance, there are methods apart from the traditional way of running that can greatly decrease injury and pain caused by impact. There are many different types of material used in shoes that can have varying results. Cushioning foam materials like PORON® VIVE® from Rogers Corporation will spread the GRF over more time, thus diminishing the impact curve and reducing the peak GRF felt by the body.

Besides changes in shoe cushioning, one method of reducing GRF is barefoot running, which has been rapidly gaining popularity. Barefoot running reduces ground reaction forces because when running barefoot, it is easier and more natural to run in a forefoot strike pattern, as opposed to the typical heel strike pattern. Running with the forefoot strike pattern reduces impact injuries by eliminating the force of impact in the heel strike, and balancing out the exerted force for the entirety of the step.

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For barefoot running to be safer, runners must use a forefoot running pattern. Many injuries have resulted from runners switching to running barefoot but neglecting to change from their original heel strike pattern. Since the impact is no longer protected by a shoe, stress is put on the tendons, bones and ligaments, which can often result in pain and injury.

Another method is to use a running shoe that differs from the traditional padded shoe — a minimalist running shoe. This type of shoe is meant to simulate the feeling of running barefoot by eliminating heavy cushioning that weighs down the feet. These shoes allow the runner to run in a forefoot strike pattern, reducing the injuries caused by heel strike.

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Traditionally cushioned running shoes shouldn’t be discounted as inadequate or out of date, there are many benefits to wearing them. Heavy cushioning reduces impact on joints, especially knee joints. Cushioning also does a good job of protecting the body from impact pain in general. In addition, the use of impact-absorbing material in running shoe insoles greatly reduces GRF peak impact and ground reaction force loading rate. All resulting in less injuries and more comfort while running.

The body’s ability to control leg stiffness can keep the force of impact the same over a wide variety of shoe and ground cushioning conditions, but this doesn’t change the peak forces on the bottom of the foot. If the cushion of a shoe is too thin, the peak plantar pressures are higher. This could potentially cause injury and is the reason why barefoot running and running in minimalist running shoes could be dangerous if the running pattern is not changed with the shoe style.

For a period of time, sales of traditionally cushioned running shoes were dropping while minimalist running shoe sales rose, but now some runners are switching back to more cushioned shoes as they appreciate the cushioned comfort of traditional running shoes over the lighter feel of the minimalist shoes.

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The above data shows the effect GRF has depending on different types of shoes.

Each runner must find which shoe works best for them and their running pattern. Often trying both shoe and running styles is helpful in determining what works best for each individual. Whether the runner prefers the natural feel of barefoot running with a forefoot strike pattern, or the comfort of having cushioned soles that prevents jarring impact and joint pain their feet must be protected so that they can be free to run without pain and injury. What good are the benefits of running if they’re too busy wrapping ankles and icing injuries?

 

Dave Sherman

Dave Sherman

Technical Design Solutions Manager at XRD® Impact Institute
Dave Sherman is the Innovation Leader at the XRD® Impact Institute - the research, design and testing facility of XRD® Impact Protection Technology. His experience involves a wide variety of foams including polyethlyene, polypropylene, EVA, rubber, polyurethane, silicone, and melamine. He has a Chemical Engineering degree from MIT and an MBA from RPI, as well as over 30 years of experience in the business of developing material solutions to meet demanding customer needs.

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