When looking at over a hundred robot designs many make the same mistake. They get the legs right in movement but fail on syncing them with rest of the body.
That would be the twisting of the waist and arms swinging. The upper body aids in balance when walking kind of like a tail does for a cat.
As one side foot steps forward the arm on the same side swings back .
Here is a web site to show this as animation of body walking.http://www.biomotionlab.ca/Demos/BMLwalker.html
Video of robot using that.
HRP-4C & HRP-2 Promet (ROBOFES) http://www.youtube.com/watch?v=E1DuJQL8spY