Originally Posted by Rowan

Well, those bone-shaker roads are among the reasons why your bones are so healthy, I would suggest.

From my understanding, it's the impact that encourages bone density, as in the leg bones, for instance, resisting force as the feet hit the ground running or walking. Weight lifting, to me, is not what this about because the muscles, tendons and ligaments are tending to take the load, rather than the skeletal structure.