July 9, 2016 - TCO
Running Shoe Myths
By Paul Langer, DPM
By far, running shoes create more confusion than any other type of footwear. Most people have learned about running shoes through a trial-and-error process. They combine information from friends, from shoe sales people, from running magazines, online reviews, and marketing messages and then try to sort through the overwhelming number of shoe choices. For some it’s no problem. Fo others it can be a frustrating, tedious process. And to add injury to insult ,many runners sustain an injury even after carefully evaluating and selecting their shoes. I’ve always maintained that running shoes are by far the most difficult piece of sports equipment to buy. There just isn’t any other piece of equipment that directly affects your health and performance on literally every step and with the disproportionately high rate of running inuries compared to other sports, none is more important. Since there are so many misconceptions and fallacies about running shoes, the Running Shoe Myths postings will be an ongoing part of this blog. I will likely start with the most common myths and work my way toward the more obscure.
Myth #1: Cushioning is the most important function of a running shoe
Believe it or not, the human body is amazingly efficient at absorbing the impact forces of running without any artificial assistance at all. This isn’t to say that cushioning doesn’t have some benefits but it may not be as important as was once thought. In fact, if cushioning was so good for us why are runners still injured at the same rate in 2009 as they were back in the early 1970’s when running shoes had dramatically less cushioning?
Before addressing the myth of cushioning lets first look at how the body absorbs running impact without shoes. Impact absorbtion begins with preactivated muscle contractions which anticipate the landing while the leg is still in the air, upon contact the plantar fat pad on the bottom of the foot cushions impact, then muscles contract further, joints flex and rotate in a precisely timed sequence extending from the foot to the ankle to the knee, hip and then spine. All of this occurs in less than half a second on every foot strike and 1,000 to 1,500 times per mile. Efficient impact absorbtion requires; balanced muscle contractions, proper range-of-motion of joints and flexibility of tendons/ligaments. Proper joint alignment is crucial for efficient, injury-free running. The cushioining of running shoes has a negative effect on joint alignment.
We don’t often think of our feet as sensory organs but the feet sense the landing surface – it’s geometry and it’s density. Those sensory input signals then send messages to the joints and muscles to help them adapt to the landing surface. For example, concrete is significantly harder and flatter than a dirt path. Our body does not experience as much ground reaction force upon impact on the dirt path and so the specialized nerve fibers (called proprioceptors) embedded in the foot send signals to the structures above on the best strategy for adapting to the surface characteristics. If you have ever unexpectedly stepped onto a different surface you have felt the varience of how your body absorbs impact under changing conditions. The cushioning of running shoes has a negative effect on proprioception.
Now back to the cushioning in running shoes. Based on the above scenario, it should be obvious that putting shoes on our feet will change how we absorb impact. Not only do shoes dampen sensory feedback but the more cushioned they are, the more they flex and compress underneath the feet. Runners land with 2.5 to 3 times their body weight on every foot strike. So a 100 lb. runner will land with up to 300 lbs. each time their foot hits the ground. The thick foam platform of a cushioned running shoe elevatates the foot above the ground and compresses unevenly. This uneven compression causes instability and so the runner must now absorb impact while their joints are in less than optimal alignment. The consequence of this is that the collapsing foam causes joints to fall out of alignment and increases workload on tendons, muscles and cartilage. Basically, all the structures of the supporting leg have to work harder to overcome the de-stabilizing effects of the cushioning. Research has confirmed that cushioned running shoes alter our alignment, muscle activation, sensory feedback and impact absorption strategies.
Some research compares running in shoes to running barefoot while some studies simply observe and gather data on the changes with shoes of varying levels of cushioning. One of the most obvious differences of running barefoot versus running in cushioned shoes is that 80% of runners in cushioned shoes land on their heels but barefoot runners land on their forefoot. These two landing patterns require two distinctly different strategies for absorbing impact. Heel strikers require more knee flexion to absorb impact while forefoot strikers use their calf muscles more.
So how much cushioning is too much? It’s hard to say. Human gait is so unique that runners do not respond in a systematic way to varying levels of cushioning in footwear. What may be too much cushioning for one runner may be just right for another. And to make it even more confusing, there is no reliable way to predict how much cushioning is appropriate. As a general rule of thumb, stabilizing devices like medial posts, dual density midsoles and trussic systems, and outsole flex grooves as well as thinner midsole designs, tend to mitigate some of the negative effects of cushioning.
Because of the de-stabilizing consequences of cushioning, I advise 90% of my running patients to use stability running shoes. I tell them to look for shoes that combine stability devices such as medial posts and dual density midsoles with cushioning. Stability running shoes, while still less stable than running barefoot, at least are less unstable than cushioned running shoes.
So the most important function of a running shoe is not to cushion but to protect the foot from the landing surface and allow our body to absorb impact in its own naturallyefficient manner.
Myth #2: Outsole Wear Patterns are Important and Must be Evaluated When Purchasing New Shoes
While shoe wear patterns have been touted by some as a crystal ball through which an observer can magically see a runner’s past, present and future, the sad fact is that 80% of runners have the same type of wear pattern. Only the most severe over-pronators and over-supinators show unusual wear patterns. The value of wear pattern evaluation has been greatly overstated in the running community.
To an untrained eye, wear to the lateral heel would be interpreted as a sign that the runner is not overpronating. However, the foot is almost never fully pronated when the heel is striking the ground so one cannot expect to see wear in the heel as an indication of how much a runner pronates. A trained observer who truly understands the biomechanical function of the lower extremity can see much more by doing a physical exam which includes watching a runner stand, walk and run barefoot. After this has been done, checking the wear pattern of the shoe may yield other clues but these clues should only confirm what they have already picked up in the exam – not provide some magical enlightenment.
Too many people pretend that wear patterns are the end-all, be-all of finding the right running shoe. In my experience, the less someone knows about biomechanics and running footwear, the more emphasis they place on wear pattern evaluations.
Myth #3: Pronation is Bad but a Simple Test can Tell us if We Overpronate
By far the most confusing concept among runners is the concept of pronation. I’ve had patients in clinic who were practically pronating right out of their shoes insist to me that they did not overpronate. The confusion is compounded by well-meaning but misinformed journalists, coaches, internet sites, some medical professionals, and running store employees who attempt to clarify a very complicated concept. To be perfectly honest, I was well into my 2nd year of podiatry school before I started to truly grasp the complex movement of the foot and ankle that is known as pronation.
Running websites and magazines tout a test where the footprint is assessed in a standing position after the foot is wet. The wet foot or wet paper towel test has been described as the best way to assess overpronation but while it is better than nothing, it is not really a reliable way to assess overpronation. Like shoe wear patterns (see myth #2), only the most extreme overpronators and underpronators are easily identified and the rest of us fall within a middle range. Within this middle range there is a huge variation in the amoiunt of pronation present. It is inadequate to say people in the middle range are “neutral.”
Never forget that pronation is our friend. Without pronation (and its counterpart – supination) none of us would be capable of running at all. Pronation is the first and most important event in a chain of events that allows our body to absorb the impact forces of running. So pronation is normal and good but too much pronation is abnormal and bad. If the feet over-pronate the whole complex and precisely-timed chain of events that occurs between the foot and the head (yes, the impact forces of footstrike travel all the way to the head) is thrown off. This can, at the least, make a runner less efficient and quicker to fatigue and at worse, make a runner vulnerable to injury.
So what is pronation? Pronation is a 3-dimensional movement of the foot and ankle that occurs as the foot is beginning to contact the ground and continues until the heel starts to lift to transfer weight to the forefoot. The foot is only in contact with the ground for half a second or less when running and for 70% of that time the foot is pronating and during the other 30% it is supinating. A pronating foot is often referred to as a “mobile adapter” because it unlocks joints and becomes flexible in order to adapt to the terrain and absorb the impact of footstrike. Conversely, a supinating foot is known as a “rigid lever” because it locks joints and stabilizes the foot providing a firm foundation to propel the body forward. The human foot can convert itself from these two extremes in hundredths of a second, thousands of times per mile.
Some people describe pronation as “rolling in” and supination as “rolling out” which is an oversimplification but as good of a description as any. Some describe pronation as a collapsing arch but pronation is really much more complicated than that. Pronation also involves inward tilting (or eversion) of the heel, outward movement (or abduction) of the forefoot, upward bending (or dorsiflexion) of the ankle and internal rotation of the lower leg. A collapsing arch is much easier to see than these other things which is why so much attention has been focused on what the arch is doing during the weightbearing portion of gait. Unfortunately, some inexperienced or untrained people who do gait assessments in running shoe stores do not understand that it is possible to have a low arch yet not over-pronate or conversely, to have a high arch and still over-pronate.
What then is “over-pronation?” If the foot has pronating too much or too long, it has over-pronated. The overpronated foot will not be able to supinate enough or it will supinate too late. This means that the foot is unstable. So instead of the runner propelling themself forward with a “rigid lever” they are pushing off of a “mobile adapter” which is much less stable and much less mechanically efficient. Imagine the difference between running in sand and running on a track. It takes much more effort and puts more strain on the muscles, tendons and joints to run on sand. The effect of running on an over-pronated foot is that muscles will work harder to stabilize the unstable foot and tendons and ligaments will be stretched longer and harder as well. This can lead to injuries like plantar fasciitis or achilles tendonitis. The exaggerated rotation that occurs with over-pronation can also place strain on the knees contributing to iliotibial band syndrome or patelofemoral pain.
Those who run must not lose sight of the fact that biomechanical research shows that running shoes facilitate pronation. The topic of how footwear affects pronation will be covered in a future post.