The following is from A Havard Study
What about surface hardness? Our ancestors didn???t run on pavement.
A common perception is that running on hard surfaces causes injuries, but runners typically adjust leg stiffness so they experience the similar impact forces on soft and hard surfaces. Further, forefoot and some midfoot strikers hit the ground in a way that generates almost no collision forces even on hard surfaces like steel. You can run barefoot and heel strike on a soft beach or lawn, but most natural surfaces are much harder and rougher. With proper forefoot or midfoot strike form, running on hard, rough surfaces can be comfortable and safe.