Take notice of the fact that the front leg reaches as far back as it does forward and that the rear legs match the movement of the front, reaching as far forward and back as do the front. Especially notable is the power being transmitted from the rear movement, through the back at the loin to the front, propelling the dog forward. It also gives a slight lift to the front, enabling that spectacular front reach.  Also note the bitch's head is slightly lowered and her croup more rounded in appearance.