Originally Posted by Dchiefransom
Maybe someone with an engineering degree can tell us why this is not true. A human shouldn't be heavy enough to cause any deflection in the asphalt. Also, with modern day running shoes, there should be no effect of even concrete on the body.
I think the difference people feel is from not coming down and going up every time a curb is crossed.
Actually I do have an engineering degreen (general with mechanical emphasis) and I don't have any doubt that it is true to an extent. The board and hammer examples noted above demonstrate that quite well. However, my experience suggests that there must be some amount of technique involved for runners to be able to handle even asphalt. I have never been a runner per se but when in college I did play soccer and had to run a lot.. I know that
I can't run on hard surfaces (certianly not concrete) for very long at all if I don't want considerable pain. I can however run for extended periods on softer surfaces (dirt and grass fields, hardwood gym floors, etc).