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Asphalt or Concrete, Which to Run On?


Here's one for which every running shoe shop employee thinks they know the best answer.
If you just apply a little common sense, and physics of course, you can figure out what's best for your training be you a 60 mile per week athlete or one with lesser aspirations.





Ready? They're equal.  Since both concrete and asphalt are easily 1,000 times harder than the sole of your new model running shoe, there's no significant hardness difference.  But having said that, blind fold an experienced runner, have him/her run on each surface, and even blindfolded they can tell you the difference.  Read on.


Kona concrete conveyor




There's this number called Young's modulus of elasticity. I'll reproduce it here in case you'd like to use it for your shopping list, to calculate the gas mileage in your Jeep, or perhaps the proper pH of the pool.


Young's Modulus




It's the measure of stiffness of a solid material. 

If you were to make a quick pit stop by Google you'd find a real range of answers like:



Livestrong  "The impact to your body's joints as you run is an important factor to consider. Although concrete and asphalt are each hard surfaces, concrete is harder and might result in more joint pain."


Runners World forum  "With all other factors being the same...the difference between the two surfaces is like the difference between a runner weighing 160 lbs or weighing 165 lbs." And I thought "heck...as a complete package...I probably gain 5 lbs from summer to winter just in extra clothing." Me, I don't avoid concrete surfaces."


Or the one that makes the most sense scientifically:


Slowtwitch  Johanthan Toker, Phd.  "The difference between concrete and asphalt is a bit like the difference between a standard HDTV and higher resolution TV, where the limiting factor becomes the eye's ability to observe the difference. The difference can be measured, but the difference is not significant in the greater context of the situation. In the case of running, both concrete and asphalt are very hard and deflect very little. The fact that one deflects a tiny bit more than the other scientifically does not translate to an observable difference in impact, especially when running is considered to include the impact absorbed by a running shoe and the sole of the foot."


So if we look at the quote that may best sum this up, from Paul Osepa*  


In running shoes, training on concrete is like adding one 
extra stride's worth of shock for every every thousand 
strides that you would take on asphalt, or about one stride per mile.
Since the cushioning difference between any two shoe models
is much more that 0.01%, I submit that shoe choice, and not
surface choice, is the only thing that matters for injury prevention
on hard surfaces.


It's worth noting that concrete is generally the most consistent surface material, while asphalt is typically cambered. 


But, can an experienced, blindfolded runner tell the difference between running on concrete versus asphalt?  Absolutely.  Maybe it's the friction difference between a porous surface and one that's less so.  Maybe it has to do with the fact that many asphalt roads are cambered, angled toward the curb for drainage.  Possibly the way a foot strikes a slightly porous substance is different.  I don't know.  But there's a difference in feel.  That said, a runner doesn't need to choose one over the other to have a successful workout without fear of increasing the potential for injury.  But if you have the option of grass, dirt or the track, I'd take it.



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*References:

Paul Osepa, Cool Runninghttp://www.chemcosystems.com/epoxy.html
http://physics.uwstout.edu/strength/tables/cyoungs.htm



More J. Toker

The difference between concrete and asphalt is a bit like the difference between a standard HDTV and higher resolution TV, where the limiting factor becomes the eye's ability to observe the difference. The difference can be measured, but the difference is not significant in the greater context of the situation. In the case of running, both concrete and asphalt are very hard and deflect very little. The fact that one deflects a tiny bit more than the other scientifically does not translate to an observable difference in impact, especially when running is considered to include the impact absorbed by a running shoe and the sole of the foot.

The compressibility of rubber, EVA and a sock have considerably more contribution to the impact transmitted to the foot within the shoe than the difference between concrete and asphalt. Consider that the difference in hardness between concrete and asphalt is equivalent to adding less than 1mm of extra rubber to the sole of a shoe.

Beyond these hard surfaces, there are significant differences between road and track, trail, grass and sand. I would submit therefore that the goal of a runner trying to reduce the hardness of a surface explore these other options. 

For example, dirt trails have other benefits too, working the body's proprioception and dynamic lateral movements and stimulating the brain with changing conditions – reconnecting with nature, some might say. Barefoot running on grass or sand is another combination that is sure to reduce the force impact and trigger further changes in running form.


As studies have shown, our bodies adapt to running surfaces. Provided good biomechanical form is maintained, any running surface will work. It's also nearly impossible to change somebody's mind once they have made it up. You may disagree based on your personal experience – that's fine. As for me, I'll stick to the dirt trails and looking for mountain lions, or leaving footprints on the beach.


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