Originally Posted by
sharktrack
That's a serious reason people have? What kind of deformation does somebody expect under what, 70kg? If there's enough deformation to actually notice in your joints with that weight I'd expect a car traveling over it to deform the road like sand! Now that reasoning for running on grass I'd buy
Google running on asphalt vs. concrete--you'll be amazed how much discussion of this there is.
Concrete is a much harder surface, but I don't see how that matters if your feet can't "bend" asphalt.
Your logic on cars vs. feet is a bit off, however. Cars roll, feet strike, so running imposes a multiplier effect in force per step while cars travel smoothly, plus the heel strike area is much smaller than the contact patches on 4 tires riding on the road. I think the relevant comparison might be a horse running on an asphalt road, but I know even less about horses than I do running.