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Tuesday, November 30, 2010

Is cushion the devil?

I found a good study by Paul Langer (DPM), and while he still recommended stability shoes as more important than cushioned shoes (I obviously disagree as I think both features are bad), he had some good statements and findings regarding the impact of cushion on running shoes.

This is a specific issue that is very close to my heart and something I continue to focus on. On one hand, cushion can feel so good but on the other the hand, it could be at the crux of the injury issue.

I quoted parts of the article and commented on others. The major take- away for me was: "Research has confirmed that cushioned running shoes alter our alignment, muscle activation, sensory feedback and impact absorption features.”

Here's, the 2 compelling conclusions related to the negative impacts
of cushioning.

1. The cushioning in running shoes has a negative effect on joint alignment.

“Impact absorption begins with pre-activated muscle contractions which anticipate the landing while the leg is still in the air and 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 absorption 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 cushioning in running shoes has a negative effect on joint alignment.”

“The thick foam platform of a cushioned running shoe elevates 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. “

This makes perfect sense to me because basically all shoes negatively impact balance and if we are not perfectly balanced then joints are not optimally aligned. Why else do we exhibit our best balance when barefoot? As you add more to the shoes, it has a degrading impact on balance, especially as you add excessive cushioning, heel differential, arch support, etc. This could easily explain why I have knee tension with cushioned racing shoes like the Nike Zoom Streak XC vs. the Evo where I’ve never experienced knee tension, as it may come down to overall balance and joint alignment and, for me, when it’s slightly off, the misalignment impacts my knees (and probably other parts of my body).

2. The cushioning of running shoes has a negative effect on proprioception.

“We don’t often think of our feet as sensory organs but the feet sense the landing surface – its geometry and its 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 variance of how your body absorbs impact under changing conditions. The cushioning of running shoes has a negative effect on proprioception.”

Again, this makes perfect sense to me. The sensory organs are blocked at an ever increasing level as we add more and more cushion or other technology underneath the foot.

So the question is how much cushioning is too much. Basically, any shoe has some type or level of cushioning, even KSOs, Evo’s, Feelmax’s and others but there’s a major difference between the cushion on the soles of those shoes vs. more traditional racing, stability or motion control shoes.

“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. “

What sticks in my mind is that the body is designed to absorb impact without any artificial or technological assistance. And, all the data I’ve seen shows that, even with the most conservative approach, runners are, at a minimum, injured at the same rate in 2010 as they were back in the early 1970’s when shoes had dramatically less cushioning, support and stability.

I know the standard response, “well, modern shoes allowed more people to run.” I could write an entire paper on why that response is insufficient and not even relevant but I’ll leave that to another day.



  1. Do you have a link to the study?

  2. Tuck, I'll send you an email with the studies I read today . . . some interesting stuff. I'm really stuck on the "balance," issue as there is no way to have optimal balance in cushioned and heel built up shoes.

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