[Shimpy]

Originally Posted by GoodLife

Jonathan Toker, PhD, presents the scientific evidence behind surface hardness - stating that "the hardness difference between concrete and asphalt is insignificant when running in shoes, because the cushioning afforded by shoes far exceeds any cushioning provided by those surfaces."

Here, once an for all, is the proof that running on asphalt
has no advantage over concrete, since they are both
at least a thousand times harder than your running shoe.
References:
Epoxy Asphalt for Orthotropic Steel Bridge Decks | ChemCo Systems
http://physics.uwstout.edu/strength/tables/cyoungs.htm
Comp. modulus of elasticity, or Young's modulus for materials:
Rubber (average) = .4 (k.p.s.i.)
Composite Asphalt = 380
Wood (compression along grain) = 1,500
Concrete = 4,500
Steel = 30,000
Using these numbers, this is the percentage of energy that is
absorbed by a rubber-based shoe running over each of
these surfaces:
Shoe Surface
Asphalt 99.89% 0.11%
Wood 99.97% 0.03%
Concrete 99.99% 0.01%
Steel >99.99% 0.001%
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.

Thanks, I just knew to myself that running on asphalt was easier on joints was BS.