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Why Running Shoes Don't Work with Steve Magness: Part 2
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Today at Boddicker Performance is a continuation of Steve Magness’s great article looking at the role of impact forces on controling the mechanics of running. Enjoy. -Carson Boddicker Impact Forces: The picture gets cloudier: But it’s not as simple as described above. Further complicating the impact force idea is that when looking at injury rates of those running on hard surfaces or soft surfaces, there appears to be no protective benefit of running on soft surfaces. Why is this? Because of something called pre-activation and muscle tuning which will be discussed below. Supporting this data, other studies have shown that people who have a low peak impact have the same likelihood of getting injured as those with a high peak impact force (Nigg, 1997). If you want to complicate things even further, impact seems to be the driving force between increased bone density. As a coach or trainer this should make sense. The bone responds to the stimulus by becoming more resistant to it, IF the stimulus is not too large and there is enough recovery. Underestimating our Body: Impact forces as feedback: Back to the question I asked earlier: How can impact forces not change based on shoe sole softness and why isn’t running on hard surfaces lead to more injuries? The problem is, once again, we underestimate the human body! It’s an
amazing thing, and we never give it the credit it deserves. The body
adapts to the surface that it’s going to strike, if you give it a
chance. The body adapts to both shoe and surface adjusting impact
forces via changes joint stiffness, the way the foot strikes, and a
concept called muscle tuning. What all of this means is that the body adapts via sensory input. It
has several different adaptation methods. A shoe influences how it
adapts. The shoe is not doing anything to alter cushioning, it is
simply altering how the body responds to impact. It’s a significant
mindset jump if you think about it. Here’s the summary: Quickly, this topic could not be complete without a brief mention of barefoot running. An interesting thing to note is that the initial peak impact force is absent in barefoot running when compared to running with shoes. What this means is that, the impact forces look like (A) for shoes and (B) for barefoot. That initial little blip in A is the initial impact force. There is a hypothesis that this initial impact force is related to injuries. A recent study by Squadrone et al.(2009) compared running shoes,
barefoot running, and running in Vibram Five Fingers. They demonstrated
reduced impact forces, shorter ground contact and stride length, but
increased stride frequency while running barefoot (and in Vibrams) as
compared to running with shoes. This is not unexpected, but shows that
running shoes do in fact alter our normal strides. An interesting point
is the reduction in stride length but increase in stride frequency.
Shoes tend to promote this longer stride at a consequence of ground
contact times and frequency. This happens because of changes in
feedback signaling, increased likelihood to land on heel stretched out,
increased weight, all of which lead to longer times on the ground. It’s
interesting to note that elite runners all have short ground contacts
and high frequencies (as demonstrated by the often quoted Daniels study
of 180 strides per minute). Another recent study found that knee flexion torque, knee varus
torque, and hip internal rotation torque all were significantly greater
in shoes compared to barefoot. What does all of this mean? Potentially,
this means more stress on the joints in this area. Jay Dicharry put it
best when he said: The one thing that non-barefoot/heel strike proponents use to dismiss midfoot striking/barefoot running is the Achilles tendon. They say, correctly, that the load on the Achilles is higher in midfoot striking runners. The Achilles is meant to take a large load. The problem is we’ve weakened the Achilles through years of wearing shoes with their elevated heels. Essentially, we’ve created the Achilles problem with the shoes meant to prevent it. The Achilles is designed to operate in a rubber band like fashion. . During impact such as the braking or contact phase of running, the achilles tendon stores energy and then subsequent releases that energy via recoil during the take off phase of running. The Achilles, can store and return approximately 35% of its kinetic energy (Ker, 1987). Without this elastic storage and return, the oxygen uptake required would be 30-40% higher! So, in terms of performance why are we trying to minimize the tendonous contribution? It’s like giving away free energy. Running shoes do not utilize the elastic storage and return as well as barefoot or minimal shoes. More energy is lost with shoes than with barefoot running (Alexander and Bennett, 1989). In addition, in some models of shoes, the arch is not allowed to function like a spring. The arch of the foot can store around 17% of kinetic energy (Ker, 1987). Given these results, its not surprising that running barefoot when compared to running with shoes is more efficient. Several studies have shown a decreased VO2 at the same pace with barefoot running, even when weight is taken into account. This should be no surprise as I mentioned above, without elastic recoil VO2 requirement would be 30-40% higher. Running in a minimal shoe allows for better utilization of this system. So, the take away message is that shoes change natural mechanics to one that creates mechanical changes that are not optimal for running fast (decreased stride frequency, increased ground contact, decreased stiffness of the system, decreased elastic contribution, and on and on). Tying it together with elites: Looking at elite athletes, when racing and training, they generally have higher turnover, minimal ground contact time, and a foot strike that is under their center of gravity. Since the majority of elites exhibit these same characteristics while racing, it makes sense that this is the optimal way to run fast. So, why are we wearing footwear that is designed to increase ground contact, decrease turnover, and promote footstrike out in front of the center of gravity? I have no idea. Conclusion: In conclusion, I’m not some fanatic saying everyone ditch shoes now. Chances are you’ve been running in shoes for 20+ years. Your bodies done some adapting during that time. You’ve got to gradually change if you want to undue some of the changes. The purpose of this article wasn’t to talk about the benefits of barefoot running. Instead it was to point out the problems with Running Shoe classification. It’s based on a cushioning/pronation paradigm that simply is not as true as they want us to believe. That paradigm needs to be reevaluated. It’s not founded on good science but rather initial ideas that made sense with no science behind them, but upon further review may not stand up to testing. A recent study found that using the good old shoe classification system that everyone uses, had little influence on injury prevention in a large group of Army Basic Training participants (Knapik, 2009). They concluded that selecting shoes based on arch height (like all major running magazines suggest) is not necessary if injury prevention is the goal. I guess that means the systems broken… Where do we go and how do we fix it? I have no idea. Sorry, no genius answers here. My inclination is that we aim for letting the foot function how it is meant to function, or at least come up with some shoe that may alter foot mechanics but while still allowing feedback/functionality of the body. The first step is looking at the foundation on which running shoes are built upon, the motion control, stability, and cushioning paradigm. My take is that it needs to be reevaluated. I’m going to end with something I’ve already said, but it’s an important concept to get across: The body is more complicated and smarter than we give it credit. Be sure to check out Steve’s Blog and BoddickerPerformance.com for more great information!
Best, Carson Boddicker
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