I wasn't talking about the heel strike, it is understood that this is about barefoot running. So the strike is on the ball of the foot. I was just saying that even striking the ball of the foot many times against concrete is a lot harder on the feet than doing the same on grass, mud, or sand.<p>The idea behind barefoot running is revert to the conditions for which the human leg has been adapting to for many thousands of years. My argument was that perhaps we haven't yet adopted to very hard surfaces, such as asphalt or concrete sidewalks ...