Tight Calves, this is something I commonly see in runners transitioning to a forefoot gait. The real trick is it is not a forefoot strike so much as a parallell landing. In this video Danny Abshire explains proper foot placement while natural running. Danny Abshire is a Running Form Guru, and the maker of Newton Running Shoes. If you have not checked out Newtons Running Form Fridays on YouTube you definitely should.
[youtube=http://www.youtube.com/watch?v=LTLVuq8XOdM]